International Journal of Rotating Machinery The latest articles from Hindawi Publishing Corporation © 2015 , Hindawi Publishing Corporation . All rights reserved. Analysis and Simulation on UMP and EMT Characters of Turbogenerator under Axial Air-Gap Eccentricity Mon, 23 Nov 2015 12:24:13 +0000 The purpose of this paper is to investigate the effect of the axial air-gap eccentricity (AAGE) on the electromagnetic characters such as the axial unbalanced magnetic pull (UMP) and the electromagnetic torque (EMT). Firstly, the theoretical model of AAGE is set up, and the formulas of the axial UMP and EMT are deduced. Then the simulation study of a SDF-9 nonsalient pole synchronous generator is taken with Ansoft Maxwell to calculate the detailed axial UMPs and EMTs under normal condition and five AAGE conditions, respectively, with 2 mm to 10 mm rotor displacements. It is shown that an apparent axial UMP will be produced due to AAGE, while EMT and the phase current will be decreased. In addition, the magnetic flux density (MFD) on the stator end and the rotor end, which are more far from the center position of the stator core in the axial direction, will be decreased, while the MFD on the other ends will be generally kept stable. As AAGE develops, the axial UMP will be increased, while EMT and the phase current will be decreased. The proposed work offers a reference for the fault diagnosis and monitoring on AAGE. Yu-Ling He, Wei-Qi Deng, and Gui-Ji Tang Copyright © 2015 Yu-Ling He et al. All rights reserved. Flow Modeling in Pelton Turbines by an Accurate Eulerian and a Fast Lagrangian Evaluation Method Mon, 16 Nov 2015 13:55:46 +0000 The recent development of CFD has allowed the flow modeling in impulse hydro turbines that includes complex phenomena like free surface flow, multifluid interaction, and unsteady, time dependent flow. Some commercial and open-source CFD codes, which implement Eulerian methods, have been validated against experimental results showing satisfactory accuracy. Nevertheless, further improvement of accuracy is still a challenge, while the computational cost is very high and unaffordable for multiparametric design optimization of the turbine’s runner. In the present work a CFD Eulerian approach is applied at first, in order to simulate the flow in the runner of a Pelton turbine model installed at the laboratory. Then, a particulate method, the Fast Lagrangian Simulation (FLS), is used for the same case, which is much faster and hence potentially suitable for numerical design optimization, providing that it can achieve adequate accuracy. The results of both methods for various turbine operation conditions, as also for modified runner and bucket designs, are presented and discussed in the paper. In all examined cases the FLS method shows very good accuracy in predicting the hydraulic efficiency of the runner, although the computed flow evolution and the torque curve exhibit some systematic differences from the Eulerian results. A. Panagiotopoulos, A. Židonis, G. A. Aggidis, J. S. Anagnostopoulos, and D. E. Papantonis Copyright © 2015 A. Panagiotopoulos et al. All rights reserved. Dynamic Characteristics Analysis of the Coupled Lateral-Torsional Vibration with Spur Gear System Mon, 16 Nov 2015 08:57:43 +0000 A sixteen-degree-of-freedom (16-DOF) lumped parameter dynamic model taking into account the gravity, eccentricity, bearing clearance, transmission error, and coupled lateral-torsional vibration is established. Based on the dynamical equation, the dynamic behaviors of the spur gear rotor bearing system are investigated by using Runge-Kutta method. The research focuses on the effect of rotational speed, eccentricity, and bearing clearance and nonlinear response of the coupled multibody dynamics is presented by vibration waveform, spectrum, and 3D frequency spectrum. The results show that the rotational frequency of the driven gear appears in the driving gear, and the dynamic characteristics of gears have obvious differences due to the effects of the gear assembly and the coupled lateral-torsional vibration. The bearing has its own resonance frequency, and the effect of the variable stiffness frequency of the bearings should be avoided during the system design. The results presented in this paper show an analysis of the coupled lateral-torsional vibration of the spur gear system. The study may contribute to a further understanding of the dynamic characteristics of such a spur gear rotor bearing system. Shihua Zhou, Zhaohui Ren, Guiqiu Song, and Bangchun Wen Copyright © 2015 Shihua Zhou et al. All rights reserved. Experimental Investigation of Stall Inception Mechanisms of Low Speed Contra Rotating Axial Flow Fan Stage Wed, 04 Nov 2015 06:33:23 +0000 The present paper is an attempt in understanding the stall inception mechanism in a low speed, contra rotating axial flow fan stage, using wavelet transforms. The rotors used in this study have relatively large tip gap (about 3% of the blade span) and aspect ratio of 3. The study was carried out near stall and at stall mass flow conditions for different speed ratios of rotor-2 to rotor-1. Unsteady pressure data from the casing wall mounted sensors are used to understand the stall inception mechanism. The wavelet transform clearly indicates that stall inception occurs mainly through long length scale disturbances for both rotors. It also reveals that short length disturbances occur simultaneously or intermittently in the case of rotor-1. The analysis shows the presence of a strong modal disturbance with 25–80% of the rotor frequency in the case of rotor-1 at the stall mass flow for all the speed combinations studied. The most interesting thing observed in the present study is that the frequency amplitude of the disturbance level is very small for both rotors. Tegegn Dejene Toge and A. M. Pradeep Copyright © 2015 Tegegn Dejene Toge and A. M. Pradeep. All rights reserved. Rotor-System Log-Decrement Identification Using Short-Time Fourier-Transform Filter Sun, 01 Nov 2015 07:22:23 +0000 With the increase of the centrifugal compressor capability, such as large scale LNG and CO2 reinjection, the stability margin evaluation is crucial to assure the compressor work in the designed operating conditions in field. Improving the precision of parameter identification of stability is essential and necessary as well. Based on the time-varying characteristics of response vibration during the sine-swept process, a short-time Fourier transform (STFT) filter was introduced to increase the signal-noise ratio and improve the accuracy of the estimated stability parameters. A finite element model was established to simulate the sine-swept process, and the simulated vibration signals were used to study the filtering effect and demonstrate the feasibility to identify the stability parameters by using Multiple-Input and Multiple-Output system identification method that combines the prediction error method and instrumental variable method. Simulation results show that the identification method with STFT filter improves the estimated accuracy much well and makes the curves of frequency response function clearer. Experiment was carried out on a test rig as well, which indicates the identification method is feasible in stability identification, and the results of experiment indicate that STFT filter works very well. Qihang Li, Weimin Wang, Lifang Chen, and Dan Sun Copyright © 2015 Qihang Li et al. All rights reserved. Design of a PID Controller for a Linearized Magnetic Bearing Mon, 26 Oct 2015 09:25:43 +0000 This paper presents the study of magnetic bearings regarding a linear model. Initially, the advantages of magnetic bearings are referenced, in relation to the existing technology. Subsequently, the linearized model of the system is presented and the need for closed loop and control of the system is clarified. This need leads to further analysis of linear controllers like P, I, D, PI, PD, and PID. For each of them, the stability of closed loop system is studied, using the characteristic equation of the system and the Routh-Hurwitz criterion. To this end, the boundary conditions for the existence of the stability of each of them are found and presented. After finding the controllers’ characteristic parameters which could provide stability to the system, simulation tests with existence of white noise follow. Finally, the proposed PID controller performance is examined, based on existing laboratory data, and results concerning the stability of this controller are presented. Theodore K. Psonis, Pantelis G. Nikolakopoulos, and Epaminondas Mitronikas Copyright © 2015 Theodore K. Psonis et al. All rights reserved. Effect of Partial Span Aspiration on the Performance of a Transonic Axial Compressor Rotor: A Numerical Study Mon, 26 Oct 2015 07:49:24 +0000 Aspiration in an axial compressor is normally regarded as sucking out the low momentum boundary layer from blade suction surface, thus lowering the chances of flow separation and consequently that of stall under off-design operation. However, the suction mass flow does not take part in useful work and leads to loss of engine power output. This paper deals with a new concept of natural aspiration to energize blade suction surface boundary layer by injecting some fluid from pressure to suction side through a part span slot on the blade. The energized boundary layer has lesser tendency to separate, thus enhancing stall margin. Numerical simulations were carried out to study the effect of aspiration slot location and geometry on the performance and stall margin of a transonic axial compressor rotor. The computational results without aspiration slot were in fair agreement with the published experimental data. The modified rotor, with part span aspiration, showed ~3.2% improvement in stall margin at design rotational speed. The pressure ratio and efficiency of the aspirated rotor dropped by ~1.42% and ~2.0%, respectively, whereas the structural analysis did not indicate any adverse effect on the blade stress distribution in the presence of aspiration slot. Vijaykumar Jain, Quamber H. Nagpurwala, and Abdul Nassar Copyright © 2015 Vijaykumar Jain et al. All rights reserved. Mathematical and Finite Element Modeling of Micro-Modification for Marine Gear Sun, 27 Sep 2015 10:09:33 +0000 Based on the computer simulation technique, this paper used the professional gear design software MASTA and finite element software ANSYS combined with the method of gear micro-modification to redesign the gear profile and eventually realized the optimization design of gear micro-modification. Then the gear transmission model of one-level reducer was established to simulate and analyze the contact equivalent stress, transmission error, and meshing impact before and after gear modification. By comparing the simulations results it is found that gear micro-modification can lower meshing impact load, reduce the vibration strength, make gear transmission steady, and improve the gear bearing capacity. By comparing the transmission error curves and meshing impact load curves before and after gear micro-modification, this helps to understand the effects of gear micro-modification on the gear transmission and provides basis references for the future redesign of the marine gears with high strength and long service life. Xiongxi Wu, Qifeng Gao, and Zesong Li Copyright © 2015 Xiongxi Wu et al. All rights reserved. Effect of Reynolds Number on Aerodynamics of Airfoil with Gurney Flap Mon, 21 Sep 2015 06:08:30 +0000 Steady state, two-dimensional computational investigations performed on NACA 0012 airfoil to analyze the effect of variation in Reynolds number on the aerodynamics of the airfoil without and with a Gurney flap of height of 3% chord are presented in this paper. RANS based one-equation Spalart-Allmaras model is used for the computations. Both lift and drag coefficients increase with Gurney flap compared to those without Gurney flap at all Reynolds numbers at all angles of attack. The zero lift angle of attack seems to become more negative as Reynolds number increases due to effective increase of the airfoil camber. However the stall angle of attack decreased by 2° for the airfoil with Gurney flap. Lift coefficient decreases rapidly and drag coefficient increases rapidly when Reynolds number is decreased below critical range. This occurs due to change in flow pattern near Gurney flap at low Reynolds numbers. Shubham Jain, Nekkanti Sitaram, and Sriram Krishnaswamy Copyright © 2015 Shubham Jain et al. All rights reserved. Component Analysis of Unsteady Hydrodynamic Force of Closed-Type Centrifugal Pump with Single Blades of Different Blade Outlet Angles Sun, 09 Aug 2015 08:35:07 +0000 Single-blade centrifugal impellers for sewage systems undergo both unsteady radial and axial thrusts. Therefore, it is extremely important for the improvement of pump reliability to quantitatively grasp these fluctuating hydrodynamic forces and determine the generation mechanism behind them. In this study, we conducted component analyses of radial and axial thrusts of closed, single-blade centrifugal pumps with different blade outlet angles by numerical analysis while considering leakage flow. The results revealed the effect of the blade outlet angle on the components of radial and axial thrusts. For increased flow rates, the time-averaged values of the pressure component were similar for all impellers, although its fluctuating components were higher for impellers with larger blade outlet angles. Moreover, the fluctuating inertia component of the impeller with a blade outlet angle of 8° decreased as the flow rate increased, whereas those with 16° and 24° angles increased. Therefore, the radial thrust on the hydraulic part was significantly higher for impellers with high blade outlet angles. Yasuyuki Nishi and Junichiro Fukutomi Copyright © 2015 Yasuyuki Nishi and Junichiro Fukutomi. All rights reserved. The Dynamic Analysis of Two-Rotor Three-Bearing System Mon, 06 Jul 2015 09:32:01 +0000 A finite element model considering the shear effect and gyroscopic effect is developed to study the linear and nonlinear dynamic behavior of two-rotor three-bearing system named N+1 configuration with rub-impact in this paper. The influence of rotational speed, eccentric condition, and the stiffness of coupling on the dynamic behavior of N+1 configuration and the propagation of motion are discussed in detail. The linear rotordynamic analysis included an evaluation of rotor critical speed and unbalance response. The results show that the critical speed and unbalance response of rotors are sensitive to coupling stiffness in N+1 configuration. In the nonlinear analysis, bifurcation diagram, shaft-center trajectory, amplitude spectrum, and Poincaré map are used to analyze the dynamic behavior of the system. The results of the research transpire that these parameters have the great effects on the dynamic behavior of the system. The response of the system with rub-impact shows abundant nonlinear phenomena. The system will exhibit synchronous periodic motion, multiperiodic motion, quasiperiodic motion, and chaotic motion patterns under rotor-stator rub interaction conditions. The dynamic response is more complicated for flexible coupling and two mass eccentricities than that of system with rigid coupling and one mass eccentricity. Jianfei Yao, Jinji Gao, Ya Zhang, and Weimin Wang Copyright © 2015 Jianfei Yao et al. All rights reserved. Study on an Undershot Cross-Flow Water Turbine with Straight Blades Mon, 29 Jun 2015 09:41:43 +0000 Small-scale hydroelectric power generation has recently attracted considerable attention. The authors previously proposed an undershot cross-flow water turbine with a very low head suitable for application to open channels. The water turbine was of a cross-flow type and could be used in open channels with the undershot method, remarkably simplifying its design by eliminating guide vanes and the casing. The water turbine was fitted with curved blades (such as the runners of a typical cross-flow water turbine) installed in tube channels. However, there was ambiguity as to how the blades’ shape influenced the turbine’s performance and flow field. To resolve this issue, the present study applies straight blades to an undershot cross-flow water turbine and examines the performance and flow field via experiments and numerical analyses. Results reveal that the output power and the turbine efficiency of the Straight Blades runner were greater than those of the Curved Blades runner regardless of the rotational speed. Compared with the Curved Blades runner, the output power and the turbine efficiency of the Straight Blades runner were improved by about 31.7% and about 67.1%, respectively. Yasuyuki Nishi, Terumi Inagaki, Yanrong Li, and Kentaro Hatano Copyright © 2015 Yasuyuki Nishi et al. All rights reserved. Simulation of a Centrifugal Pump by Using the Harmonic Balance Method Thu, 21 May 2015 11:08:40 +0000 The harmonic balance method was used for the flow simulation in a centrifugal pump. Independence studies have been done to choose proper number of harmonic modes and inlet eddy viscosity ratio value. The results from harmonic balance method show good agreements with PIV experiments and unsteady calculation results (which is based on the dual time stepping method) for the predicted head and the phase-averaged velocity. A detailed analysis of the flow fields at different flow rates shows that the flow rate has an evident influence on the flow fields. At 0.6, some vortices begin to appear in the impeller, and at 0.4 some vortices have blocked the flow passage. The flow fields at different positions at 0.6 and 0.4 show how the complicated flow phenomena are forming, developing, and even disappearing. The harmonic balance method can be used for the flow simulation in pumps, showing the same accuracy as unsteady methods, but is considerably faster. Franco Magagnato and Jinfeng Zhang Copyright © 2015 Franco Magagnato and Jinfeng Zhang. All rights reserved. Establishment of Approximate Analytical Model of Oil Film Force for Finite Length Tilting Pad Journal Bearings Wed, 20 May 2015 16:39:53 +0000 Tilting pad bearings offer unique dynamic stability enabling successful deployment of high-speed rotating machinery. The model of dynamic stiffness, damping, and added mass coefficients is often used for rotordynamic analyses, and this method does not suffice to describe the dynamic behaviour due to the nonlinear effects of oil film force under larger shaft vibration or vertical rotor conditions. The objective of this paper is to present a nonlinear oil force model for finite length tilting pad journal bearings. An approximate analytic oil film force model was established by analysing the dynamic characteristic of oil film of a single pad journal bearing using variable separation method under the dynamic oil film boundary condition. And an oil film force model of a four-tilting-pad journal bearing was established by using the pad assembly technique and considering pad tilting angle. The validity of the model established was proved by analyzing the distribution of oil film pressure and the locus of journal centre for tilting pad journal bearings and by comparing the model established in this paper with the model established using finite difference method. Yongliang Wang, Yu Gao, Ying Cui, and Zhansheng Liu Copyright © 2015 Yongliang Wang et al. All rights reserved. Advances in Measurement Techniques for Turbomachinery Flow, Heat Transfer, and Acoustics Tue, 05 May 2015 09:31:38 +0000 Nekkanti Sitaram, Giovanni Maria Carlomagno, Takayuki Matsunuma, and Mark McQuilling Copyright © 2015 Nekkanti Sitaram et al. All rights reserved. A Time Efficient Adaptive Gridding Approach and Improved Calibrations in Five-Hole Probe Measurements Mon, 04 May 2015 13:16:13 +0000 Five-Hole Probes (FHP), being a dependable and accurate aerodynamic tool, are an excellent choice for measuring three-dimensional flow fields in turbomachinery. To improve spatial resolution, a subminiature FHP with a diameter of 1.68 mm is employed. High length to diameter ratio of the tubing and manual pitch and yaw calibration cause increased uncertainty. A new FHP calibrator is designed and built to reduce the uncertainty by precise, computer controlled movements and reduced calibration time. The calibrated FHP is then placed downstream of the nozzle guide vane (NGV) assembly of a low-speed, large-scale, axial flow turbine. The cold flow HP turbine stage contains 29 vanes and 36 blades. A fast and computer controllable traversing system is implemented using an adaptive grid method for the refinement of measurements in regions such as vane wake, secondary flows, and boundary layers. The current approach increases the possible number of measurement points in a two-hour period by 160%. Flow structures behind the NGV measurement plane are identified with high spatial resolution and reduced uncertainty. The automated pitch and yaw calibration and the adaptive grid approach introduced in this study are shown to be a highly effective way of measuring complex flow fields in the research turbine. Jason Town and Cengiz Camci Copyright © 2015 Jason Town and Cengiz Camci. All rights reserved. Detection of Rotor Forced Response Vibrations Using Stationary Pressure Transducers in a Multistage Axial Compressor Sun, 03 May 2015 14:27:50 +0000 Blade row interactions in turbomachinery can lead to blade vibrations and even high cycle fatigue. Forced response conditions occur when a forcing function (such as impingement of stator wakes) occurs at a frequency that matches the natural frequency of a blade. The objective of this research is to develop the data processing techniques needed to detect rotor blade vibration in a forced response condition from stationary fast-response pressure transducers to allow for detection of rotor vibration from transient data and lead to techniques for vibration monitoring in gas turbines. This paper marks the first time in the open literature that engine-order resonant response of an embedded bladed disk in a 3-stage intermediate-speed axial compressor was detected using stationary pressure transducers. Experiments were performed in a stage axial research compressor focusing on the embedded rotor of blisk construction. Fourier waterfall graphs from a laser tip timing system were used to detect the vibrations after applying signal processing methods to uncover these pressure waves associated with blade vibration. Individual blade response was investigated using cross covariance to compare blade passage pressure signatures through resonance. Both methods agree with NSMS data that provide a measure of the exact compressor speeds at which individual blades enter resonance. William L. Murray III and Nicole L. Key Copyright © 2015 William L. Murray III and Nicole L. Key. All rights reserved. Conjugate Heat Transfer Study of Combined Impingement and Showerhead Film Cooling Near NGV Leading Edge Sun, 03 May 2015 12:45:30 +0000 A computational and experimental study is carried out on the leading edge region of a typical gas turbine NGV, cooled by a combination of impingement and showerhead film cooling. A detailed flow and conjugate heat transfer study has revealed the complex flow structure owing to the coolant-mainstream interaction and the influence of vane material thermal conductivity. The local effectiveness values obtained by the computations agreed well with the experimental data from IR thermography. The effect of blowing ratio on the overall effectiveness is found to be strongly dependent on the vane material conductivity. The effect of blowing ratio is also found to be different towards the pressure and suction sides of the stagnation region. However, the overall effectiveness is found to decrease by about 12% and 6% for low and high conducting materials, respectively, with an increase in mainstream Reynolds number from to . Dileep Chandran and Bhamidi Prasad Copyright © 2015 Dileep Chandran and Bhamidi Prasad. All rights reserved. Experimental Investigation of Factors Influencing Operating Rotor Tip Clearance in Multistage Compressors Sun, 03 May 2015 12:09:37 +0000 An analysis of compressor rotor tip clearance measurements using capacitance probe instrumentation is discussed for a three-stage axial compressor. Thermal variations and centrifugal effects related to rotational speed changes affect clearance heights relative to the assembled configuration. These two primary contributions to measured changes are discussed both independently and in combination. Emphasis is given to tip clearance changes due to changing loading condition and at several compressor operating speeds. Measurements show a tip clearance change approaching 0.1 mm (0.2% rotor span) when comparing a near-choke operating condition to a near-stall operating condition for the third stage. Additional consideration is given to environmental contributions such as ambient temperature, for which changes in tip clearance height on the order of 0.05 mm (0.1% rotor span) were noted for temperature variations of 15°C. Experimental compressor operating clearances are presented for several temperatures, operating speeds, and loading conditions, and comparisons are drawn between these measured variations and predicted changes under the same conditions. Reid A. Berdanier and Nicole L. Key Copyright © 2015 Reid A. Berdanier and Nicole L. Key. All rights reserved. Some Experimental Investigations on Gas Turbine Cooling Performed with Infrared Thermography at Federico II Sun, 03 May 2015 08:56:53 +0000 This paper reviews some experimental measurements of convective heat transfer coefficient distributions which are connected with the cooling of gas turbines, performed by the authors’ research group at the University of Naples Federico II with infrared thermography. Measurements concern impinging jets, cooling of rotating disks, and gas turbine blades, which are either stationary or rotating. The heated thin foil sensor, associated with the detection of surface temperature by means of infrared thermography, is exploited to accurately measure detailed convective heat transfer coefficient maps. The paper also intends to show how to correctly apply the infrared technique in a variety of gas turbines cooling problems. T. Astarita, G. Cardone, L. de Luca, and G. M. Carlomagno Copyright © 2015 T. Astarita et al. All rights reserved. Turbulent Kinetic Energy Production in the Vane of a Low-Pressure Linear Turbine Cascade with Incoming Wakes Wed, 18 Feb 2015 06:49:58 +0000 Incompressible large eddy simulation and direct numerical simulation of a low-pressure turbine at and with discrete incoming wakes are analyzed to identify the turbulent kinetic energy generation mechanism outside of the blade boundary layer. The results highlight the growth of turbulent kinetic energy at the bow apex of the wake and correlate it to the stress-strain tensors relative orientation. The production rate is analytically split according to the principal axes, and then terms are computed by using the simulation results. The analysis of the turbulent kinetic energy is followed both along the discrete incoming wakes and in the stationary frame of reference. Both direct numerical and large eddy simulation concur in identifying the same production mechanism that is driven by both a growth of strain rate in the wake, first, followed by the growth of turbulent shear stress after. The peak of turbulent kinetic energy diffuses and can eventually reach the suction side boundary layer for the largest Reynolds number investigated here with higher incidence angle. As a consequence, the local turbulence intensity outside the boundary layer can grow significantly above the free-stream level with a potential impact on the suction side boundary layer transition mechanism. V. Michelassi and J. G. Wissink Copyright © 2015 V. Michelassi and J. G. Wissink. All rights reserved. Heat Transfer and Friction Studies in a Tilted and Rib-Roughened Trailing-Edge Cooling Cavity with and without the Trailing-Edge Cooling Holes Sun, 14 Dec 2014 07:01:31 +0000 Local and average heat transfer coefficients and friction factors were measured in a test section simulating the trailing-edge cooling cavity of a turbine airfoil. The test rig with a trapezoidal cross-sectional area was rib-roughened on two opposite sides of the trapezoid (airfoil pressure and suction sides) with tapered ribs to conform to the cooling cavity shape and had a 22-degree tilt in the flow direction upstream of the ribs that affected the heat transfer coefficients on the two rib-roughened surfaces. The radial cooling flow traveled from the airfoil root to the tip while exiting through 22 cooling holes along the airfoil trailing-edge. Two rib geometries, with and without the presence of the trailing-edge cooling holes, were examined. The numerical model contained the entire trailing-edge channel, ribs, and trailing-edge cooling holes to simulate exactly the tested geometry. A pressure-correction based, multiblock, multigrid, unstructured/adaptive commercial software was used in this investigation. Realizable turbulence model in conjunction with enhanced wall treatment approach for the near wall regions was used for turbulence closure. The applied thermal boundary conditions to the CFD models matched the test boundary conditions. Comparisons are made between the experimental and numerical results. M. E. Taslim and J. S. Halabi Copyright © 2014 M. E. Taslim and J. S. Halabi. All rights reserved. Comparison of Common Methods in Dynamic Response Predictions of Rotor Systems with Malfunctions Tue, 09 Dec 2014 00:10:15 +0000 The efficiency and accuracy of common time and frequency domain methods that are used to simulate the response of a rotor system with malfunctions are compared and analyzed. The Newmark method and the incremental harmonic balance method are selected as typical representatives of time and frequency domain methods, respectively. To improve the simulation efficiency, the fixed interface component mode synthesis approach is combined with the Newmark method and the receptance approach is combined with the incremental harmonic balance method. Numerical simulations are performed for rotor systems with single and double frequency excitations. The inherent characteristic that determines the efficiency of the two methods is analyzed. The results of the analysis indicated that frequency domain methods are suitable single and double frequency excitation rotor systems, whereas time domain methods are more suitable for multifrequency excitation rotor systems. Hongliang Yao, Qian Zhao, Qi Xu, and Bangchun Wen Copyright © 2014 Hongliang Yao et al. All rights reserved. Influence of Spatially Varying Flow on the Dynamic Response of a Waterjet inside an SES Wed, 03 Dec 2014 00:10:08 +0000 Surface Effect Ships (SES) are a promising fuel-efficient ship technology that typically carry most of their weight on an air cushion. To accommodate its shallow draft and slender side hulls and to absorb the high thrust and power required for high-speed applications, waterjets are typically used as the primary propulsion system. A waterjet typically has a flush mounted inlet and operates under complex three-dimensional flow conditions that result in highly nonuniform flows. The objectives of this work are to quantify the flow nonuniformity and the influence of unsteady cavitation on the response of an SES-waterjet system and to investigate the effect of flow nonuniformity and cavitation on the dynamic hydroelastic response of the rotor and stator blades. The results showed that as the flow advances through the pump, the ingested boundary layer from the bottom of the side hulls becomes increasingly nonuniform, particularly between the rotor and stator. The flow nonuniformity was shown to result in hydrodynamic load fluctuations and high side forces on the rotor and stator blades. The unbalanced blade loads lead to the generation of net upward forces on the pump casing and shaft. Flow nonuniformity also leads to unsteady cavitation and unsteady blade stresses and deformations. Michael R. Motley, Brant R. Savander, and Yin L. Young Copyright © 2014 Michael R. Motley et al. All rights reserved. Effect of Blade Outlet Angle on Unsteady Hydrodynamic Force of Closed-Type Centrifugal Pump with Single Blade Tue, 18 Nov 2014 00:00:00 +0000 Geometrically, the single-blade centrifugal impeller, commonly used today as a sewage pump, is not axially symmetric. For this reason, the static pressure around the impeller fluctuates greatly when the impeller is rotating, and not only the radial thrust but also the axial thrust shows large fluctuations. Therefore, it is extremely important for the improvement of pump reliability to quantitatively grasp these fluctuating hydrodynamic forces. In this study, we investigated the unsteady hydrodynamic forces in a closed-type centrifugal pump with a single blade for different blade outlet angles using a numerical analysis that takes into account both experiment and the leakage flow. The results clearly showed the effect of the blade outlet angle on that act on the impeller. The root-mean-square value of the fluctuating component of the total radial thrust was roughly the same for whichever impeller at low flow rate, but at high flow rates, the value increased for impellers with larger blade outlet angles. Moreover, when the leakage flow rate increased with increasing static pressure around the impeller, such that the rear and front shroud parts were subject to high pressure, the absolute value of the axial thrust on both these parts increased. Yasuyuki Nishi and Junichiro Fukutomi Copyright © 2014 Yasuyuki Nishi and Junichiro Fukutomi. All rights reserved. An Air Jet Distortion Generation System Thu, 23 Oct 2014 13:03:56 +0000 An air jet distortion generation system is developed to simulate the distorted flow field ahead of gas turbine engines in ground test facility. The flow field of a system of four jets arranged circumferentially and issuing into a confined counterflow was studied experimentally and numerically. The total pressure distortion parameters were evaluated at the Aerodynamic Interface Plane (AIP) for several values of mass flow ratios. Since the total pressure loss distribution at the AIP is characteristically “V” shaped, the number of jets was increased to obtain total pressure distributions as required for gas turbine engine testing. With this understanding, a methodology has been developed to generate a target total pressure distortion pattern at the AIP. Turbulent flow computations are used to iteratively progress towards the target distribution. This methodology was demonstrated for a distortion flow pattern typical of use in gas turbine engine testing using twenty jets, which is a smaller number than reported in the literature. The procedure converges with a root-mean-square error of 3.836% and is able to reproduce the target pattern and other distortion parameters. M. Sivapragasam, S. Ramamurthy, M. D. Deshpande, and P. White Copyright © 2014 M. Sivapragasam et al. All rights reserved. Improvement of Moderately Loaded Transonic Axial Compressor Performance Using Low Porosity Bend Skewed Casing Treatment Thu, 23 Oct 2014 09:08:04 +0000 This paper presents experimental results of a single stage transonic axial flow compressor coupled with low porosity bend skewed casing treatment. The casing treatment has a plenum chamber above the bend slots. The depth of the plenum chamber is varied to understand its impact on the performance of compressor stage. The performance of the compressor stage is evaluated for casing treatment and plenum chamber configurations at two axial locations of 20% and 40%. Experimental results reveal that the stall margin of the compressor stage increases with increase in the plenum chamber volume. Hot-wire measurements show significant reduction in the turbulence intensity with increase in the plenum chamber volume compared to that with the solid casing at the stall condition. At higher operating speeds of 80% and at 20% axial coverage, the stall margin of the compressor increases by 20% with half and full plenum depth. The improvement in the peak stage efficiency observed is 4.6% with half plenum configuration and 3.34% with the full plenum configuration. The maximum improvement in the stall margin of 29.16% is obtained at 50% operating speed with full plenum configurations at 40% axial coverage. Dilipkumar Bhanudasji Alone, S. Satish Kumar, Shobhavathy M. Thimmaiah, Janaki Rami Reddy Mudipalli, A. M. Pradeep, Srinivasan Ramamurthy, and Venkat S. Iyengar Copyright © 2014 Dilipkumar Bhanudasji Alone et al. All rights reserved. A New Approach to Designing the S-Shaped Annular Duct for Industrial Centrifugal Compressor Thu, 16 Oct 2014 00:00:00 +0000 The authors propose an analytical method for designing the inlet annular duct for an industrial centrifugal compressor using high-order Bezier curves. Using the design of experiments (DOE) theory, the three-level full factorial design was developed for determination of influence of the dimensionless geometric parameters on the output criteria. Numerical research was carried out for determination of pressure loss coefficients and velocity swirl angles using the software system ANSYS CFX. Optimal values of the slope for a wide range of geometric parameters, allowing minimizing losses in the duct, have been found. The study has used modern computational fluid dynamics techniques to develop a generalized technique for future development of efficient variable inlet guide vane systems. Recommendations for design of the s-shaped annular duct for industrial centrifugal compressor have been given. Ivan Yurko and German Bondarenko Copyright © 2014 Ivan Yurko and German Bondarenko. All rights reserved. Numerical Investigation: Effect of Stator Vanes on Turbocharger Turbine Performance Tue, 14 Oct 2014 11:43:21 +0000 With reduced turbo lag and better transient response, the introduction of VTG stator guide vanes improved turbocharger performance at all the engine operating conditions. The VTG system accelerates and maneuvers exhaust gas flow to the turbine. Favorable flow conditions at turbine inlet created by vane shape improve turbine performance. At lower engine speed, it is observed that the pressure drop across vane system influences overall efficiency. Whereas at higher speed, the pressure drop and guide vane exit flow angle are found to determine the turbine efficiency. Successful practical operation of VTG system also depends on its ability to smoothly open and close the vanes at different gas loads. Stator vane shape greatly influences the smooth operability/controllability of vane system. In the present work, 3 symmetric vanes with different ratios and 2 asymmetric vanes are analyzed. The effect of geometric changes is studied from overall turbine performance as well as VTG system performance perspective. It is observed that symmetric vanes cause higher pressure drop at lower speeds leading to lower efficiency irrespective of the vane width. It is also observed that the pressure drop characteristics and vane exit flow angle are better with the asymmetric vanes, whereas the controllability of symmetric vanes is found to be superior. Analysis methodology is presented for achieving the best compromise between performance and controllability by the modification of vane geometric parameters through CFD simulations. Ganesh Yadagiri Rapolu, Siddharth Swaminathan Balachandar, and Keerthi Vallarasu Kamaraj Copyright © 2014 Ganesh Yadagiri Rapolu et al. All rights reserved. Surrogate Assisted Design Optimization of an Air Turbine Tue, 14 Oct 2014 09:15:14 +0000 Surrogates are cheaper to evaluate and assist in designing systems with lesser time. On the other hand, the surrogates are problem dependent and they need evaluation for each problem to find a suitable surrogate. The Kriging variants such as ordinary, universal, and blind along with commonly used response surface approximation (RSA) model were used in the present problem, to optimize the performance of an air impulse turbine used for ocean wave energy harvesting by CFD analysis. A three-level full factorial design was employed to find sample points in the design space for two design variables. A Reynolds-averaged Navier Stokes solver was used to evaluate the objective function responses, and these responses along with the design variables were used to construct the Kriging variants and RSA functions. A hybrid genetic algorithm was used to find the optimal point in the design space. It was found that the best optimal design was produced by the universal Kriging while the blind Kriging produced the worst. The present approach is suggested for renewable energy application. Rameez Badhurshah and Abdus Samad Copyright © 2014 Rameez Badhurshah and Abdus Samad. All rights reserved.