International Journal of Rotating Machinery The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Experimental Study of the Effect of Radially Distorted Inflow on a Contrarotating Fan Stage Wed, 26 Mar 2014 12:40:57 +0000 The paper reports results of a detailed study of hub- and tip-strong radial inflow distortion on the performance of a low speed, high aspect ratio (3.0) contrarotating fan stage. The distortion screen (placed upstream of the first rotor) covers 1/3 of the span of the blade near the hub and the casing for hub-strong and tip-strong inflow distortions, respectively. The performance of the contrarotating fan was investigated under both the radially distorted inflows and compared with the clean inflow conditions under different speed combinations of rotor-1 and rotor-2. The hub-strong radial distortion reduces the overall performance (pressure rise and efficiency) as well as the operating range by about 2 to 4% under the different speed combinations. On the other hand, it is interesting to observe that the tip covered radial distortion not only improves the pressure rise, but also increases the overall operating range by about 6 to 8%. There was, however, a 6 to 8% decrease in efficiency in this case as compared to 12 to 15% for hub-strong radial inflow distortion. The results reveal the physics of the effects of radial inflow distortion on the overall performance of the contrarotating fan stage. Chetan Mistry and A. M. Pradeep Copyright © 2014 Chetan Mistry and A. M. Pradeep. All rights reserved. Research on the Power Recovery of Diesel Engines with Regulated Two-Stage Turbocharging System at Different Altitudes Wed, 26 Mar 2014 11:27:23 +0000 Recovering the boost pressure is very important in improving the dynamic performance of diesel engines at high altitudes. A regulated two-stage turbocharging system is an adequate solution for power recovery of diesel engines. In the present study, the change of boost pressure and engine power at different altitudes was investigated, and a regulated two-stage turbocharging system was constructed with an original turbocharger and a matched low pressure turbocharger. The valve control strategies for boost pressure recovery, which formed the basis of the power recovery method, are presented here. The simulation results showed that this system was effective in recovering the boost pressure at different speeds and various altitudes. The turbine bypass valve and compressor bypass valve had different modes to adapt to changes in operating conditions. The boost pressure recovery could not ensure power recovery over the entire operating range of the diesel engine, because of variation in overall turbocharger efficiency. The fuel-injection compensation method along with the valve control strategies for boost pressure recovery was able to reach the power recovery target. Hualei Li, Lei Shi, and Kangyao Deng Copyright © 2014 Hualei Li et al. All rights reserved. Design Optimization of a Transonic-Fan Rotor Using Numerical Computations of the Full Compressible Navier-Stokes Equations and Simplex Algorithm Mon, 24 Mar 2014 06:54:10 +0000 The design of a transonic-fan rotor is optimized using numerical computations of the full three-dimensional Navier-Stokes equations. The CFDRC-ACE multiphysics module, which is a pressure-based solver, is used for the numerical simulation. The code is coupled with simplex optimization algorithm. The optimization process is started from a suitable design point obtained using low fidelity analytical methods that is based on experimental correlations for the pressure losses and blade deviation angle. The fan blade shape is defined by its stacking line and airfoil shape which are considered the optimization parameters. The stacking line is defined by lean, sweep, and skews, while blade airfoil shape is modified considering the thickness and camber distributions. The optimization has been performed to maximize the rotor total pressure ratio while keeping the rotor efficiency and surge margin above certain required values. The results obtained are verified with the experimental data of Rotor 67. In addition, the results of the optimized fan indicate that the optimum design is found to be leaned in the direction of rotation and has a forward sweep from the hub to mean section and backward sweep to the tip. The pressure ratio increases from 1.427 to 1.627 at the design speed and mass flow rate. M. A. Aziz, Farouk M. Owis, and M. M. Abdelrahman Copyright © 2014 M. A. Aziz et al. All rights reserved. Preliminary Experimental Study on Pressure Loss Coefficients of Exhaust Manifold Junction Thu, 13 Mar 2014 11:14:51 +0000 The flow characteristic of exhaust system has an important impact on inlet boundary of the turbine. In this paper, high speed flow in a diesel exhaust manifold junction was tested and simulated. The pressure loss coefficient of the junction flow was analyzed. The steady experimental results indicated that both of static pressure loss coefficients and first increased and then decreased with the increase of mass flow ratio of lateral branch and public manifold. The total pressure loss coefficient always increased with the increase of mass flow ratio of junctions 1 and 3. The total pressure loss coefficient first increased and then decreased with the increase of mass flow ratio of junctions 2 and 3. These pressure loss coefficients of the exhaust pipe junctions can be used in exhaust flow and turbine inlet boundary conditions analysis. In addition, simulating calculation was conducted to analyze the effect of branch angle on total pressure loss coefficient. According to the calculation results, total pressure loss coefficient was almost the same at low mass flow rate of branch manifold 1 but increased with lateral branch angle at high mass flow rate of branch manifold 1. Xiao-lu Lu, Kun Zhang, Wen-hui Wang, Shao-ming Wang, and Kang-yao Deng Copyright © 2014 Xiao-lu Lu et al. All rights reserved. Experimental Study of Darrieus-Savonius Water Turbine with Deflector: Effect of Deflector on the Performance Thu, 20 Feb 2014 08:10:05 +0000 The reverse force on the returning blade of a water turbine can be reduced by setting a deflector on the returning blade side of a rotor. The deflector configuration can also concentrate the flow which passes through the rotor so that the torque and the power of turbine can be considerably increased. The placing of Savonius in Darrieus rotor is carried out by setting the Savonius bucket in Darrieus rotor at the same axis. The combination of these rotors is also called a Darrieus-Savonius turbine. This rotor can improve torque of turbine. Experiments are conducted in an irrigation canal to find the performance characteristics of presence of deflector and Savonius rotor in Darrieus-Savonius turbine. Results conclude that the single deflector plate placed on returning blade side increases the torque and power coefficient. The presence of Savonius rotor increases the torque at a lower speed, but the power coefficient decreases. The torque and power coefficient characteristics depend on the aspect ratio of Savonius rotor. Kaprawi Sahim, Kadafi Ihtisan, Dyos Santoso, and Riman Sipahutar Copyright © 2014 Kaprawi Sahim et al. All rights reserved. On the Instability Threshold of Journal Bearing Supported Rotors Mon, 03 Feb 2014 12:21:55 +0000 Journal bearing supported rotors present two kinds of self-excited vibrations: oil-whirl and oil-whip. The first one is commonly masked by the rotor unbalance, hence being rarely associated with instability problems. Oil-whip is a severe vibration which occurs when the oil-whirl frequency coincides with the first flexural natural frequency of the shaft. In many cases, oil-whip is the only fluid-induced instability considered during the design stage; however, experimental evidences have shown that the instability threshold may occur much sooner, demanding a better comprehension of the instability mechanism. In this context, numerical simulations were made in order to improve the identification of the instability threshold for two test rig configurations: one on which the instability occurs on the oil-whip frequency, and another which became unstable before this threshold. Therefore, the main contribution of this paper is to present an investigation of two different thresholds of fluid-induced instabilities and their detectability on design stage simulations based on rotordynamic analysis using linear speed dependent coefficients for the bearings. Ricardo Ugliara Mendes and Katia Lucchesi Cavalca Copyright © 2014 Ricardo Ugliara Mendes and Katia Lucchesi Cavalca. All rights reserved. Analysis of the Unsteady Flow Field in a Centrifugal Compressor from Peak Efficiency to Near Stall with Full-Annulus Simulations Thu, 16 Jan 2014 08:32:41 +0000 This study concerns a 2.5 pressure ratio centrifugal compressor stage consisting of a splittered unshrouded impeller and a vaned diffuser. The aim of this paper is to investigate the modifications of the flow structure when the operating point moves from peak efficiency to near stall. The investigations are based on the results of unsteady three-dimensional simulations, in a calculation domain comprising all the blade. A detailed analysis is given in the impeller inducer and in the vaned diffuser entry region through time-averaged and unsteady flow field. In the impeller inducer, this study demonstrates that the mass flow reduction from peak efficiency to near stall leads to intensification of the secondary flow effects. The low momentum fluid accumulated near the shroud interacts with the main flow through a shear layer zone. At near stall condition, the interface between the two flow structures becomes unstable leading to vortices development. In the diffuser entry region, by reducing the mass flow, the high incidence angle from the impeller exit induces a separation on the diffuser vane suction side. At near stall operating point, vorticity from the separation is shed into vortex cores which are periodically formed and convected downstream along the suction side. Yannick Bousquet, Xavier Carbonneau, Guillaume Dufour, Nicolas Binder, and Isabelle Trebinjac Copyright © 2014 Yannick Bousquet et al. All rights reserved. Experimental and Numerical Simulation of Unbalance Response in Vertical Test Rig with Tilting-Pad Bearings Mon, 06 Jan 2014 11:11:35 +0000 In vertically oriented machines with journal bearing, there are no predefined static radial loads, such as dead weight for horizontal rotor. Most of the commercial software is designed to calculate rotordynamic and bearing properties based on machines with a horizontally oriented rotor; that is, the bearing properties are calculated at a static eccentricity. For tilting-pad bearings, there are no existing analytical expressions for bearing parameters and the bearing parameters are dependent on eccentricity and load angle. The objective of this paper is to present a simplified method to perform numerical simulations on vertical rotors including bearing parameters. Instead of recalculating the bearing parameters in each time step polynomials are used to represent the bearing parameters for present eccentricities and load angles. Numerical results are compared with results from tests performed in a test rig. The test rig consists of two guide bearings and a midspan rotor. The guide bearings are 4-pad tilting-pad bearings. Shaft displacement and strains in the bearing bracket are measured to determine the test rig’s properties. The comparison between measurements and simulated results shows small deviations in absolute displacement and load levels, which can be expected due to difficulties in calculating exact bearing parameters. Mattias Nässelqvist, Rolf Gustavsson, and Jan-Olov Aidanpää Copyright © 2014 Mattias Nässelqvist et al. All rights reserved. Effect of Mechanism Error on Input Torque of Scroll Compressor Tue, 31 Dec 2013 15:19:21 +0000 Based on the fundamental principle of plane four-bar mechanism, the force on the equivalent parallel four-bar mechanism was analyzed for scroll compressor with mini-crank antirotation, and the formula of input torque was proposed. The change of input torque caused by the mechanism size error was analyzed and verified with an example. The calculation results show that the mechanism size error will cause large fluctuation in input torque at the drive rod and connecting rod collinear and the fluctuation extreme value increases with rotational speed. Decreasing of the crankshaft eccentricity errors is helpful for reducing the effects of dimension error on input torque but will increase the friction loss of orbiting and fixed scroll wrap. The influence of size error should be considered in design in order to select suitable machining accuracy and reduce the adverse effect caused by size error. Man Zhao, Shurong Yu, Chao Li, and Yang Yu Copyright © 2013 Man Zhao et al. All rights reserved. Optimum Design of Oil Lubricated Thrust Bearing for Hard Disk Drive with High Speed Spindle Motor Tue, 31 Dec 2013 10:25:09 +0000 This paper presents the application of optimization method developed by Hashimoto to design oil lubricated thrust bearings for 2.5 inch form factor hard disk drives (HDD). The designing involves optimization of groove geometry and dimensions. Calculations are carried out to maximize the dynamic stiffness of the thrust bearing spindle motor. Static and dynamic characteristics of the modeled thrust bearing are calculated using the divergence formulation method. Results show that, by using the proposed optimization method, dynamic stiffness values can be well improved with the bearing geometries not being fixed to conventional grooves. Yuta Sunami, Mohd Danial Ibrahim, and Hiromu Hashimoto Copyright © 2013 Yuta Sunami et al. All rights reserved. A One-Dimensional Flow Analysis for the Prediction of Centrifugal Pump Performance Characteristics Sat, 07 Dec 2013 13:16:13 +0000 A one-dimensional flow procedure for analytical study of centrifugal pump performance is done applying the principle theories of turbomachines. Euler equation and energy equation are manipulated to find pump performance parameters at different discharge coefficients. Fluid slippage loss at impeller exit and volute loss are estimated. The fluid slippage is modeled by the slip factor approach using Wiesner empirical expression. The volute loss model counts friction loss associated with the volute throw flow velocity, diffusion friction loss due to circulation associated with volute flow, loss due to vanishing of radial flow at volute outlet, and loss inside pump volute throat. Models for impeller hydraulic friction power loss, disk friction power loss, internal flow leakage power loss, and inlet shock circulation power loss are considered by suitable models. Pump internal volumetric flow leakage and volumetric efficiency are related to pump geometry and flow properties. The procedure adopted in this paper is capable of obtaining performance characteristic curves of centrifugal pump in a dimensionless form. Pump head coefficient, manometric efficiency, power coefficient, and required NPSH are characterized. The predicted coefficients and obtained performance curves are consistent with experimental characteristics of centrifugal pump. Mohammed Ahmed El-Naggar Copyright © 2013 Mohammed Ahmed El-Naggar. All rights reserved. Effects of Rotation at Different Channel Orientations on the Flow Field inside a Trailing Edge Internal Cooling Channel Wed, 27 Nov 2013 14:09:10 +0000 The flow field inside a cooling channel for the trailing edge of gas turbine blades has been numerically investigated with the aim to highlight the effects of channel rotation and orientation. A commercial 3D RANS solver including a SST turbulence model has been used to compute the isothermal steady air flow inside both static and rotating passages. Simulations were performed at a Reynolds number equal to 20000, a rotation number (Ro) of 0, 0.23, and 0.46, and channel orientations of , 22.5°, and 45°, extending previous results towards new engine-like working conditions. The numerical results have been carefully validated against experimental data obtained by the same authors for conditions and Ro = 0, 0.23. Rotation effects are shown to alter significantly the flow field inside both inlet and trailing edge regions. These effects are attenuated by an increase of the channel orientation from to 45°. Matteo Pascotto, Alessandro Armellini, Luca Casarsa, Claudio Mucignat, and Pietro Giannattasio Copyright © 2013 Matteo Pascotto et al. All rights reserved. Numerical Simulation of Water Flow through a Nano-Hydraulic Turbine of Waterfall-Type by Particle Method Mon, 18 Nov 2013 09:54:42 +0000 This study simulates the flow through an impulse-type small-scale hydraulic turbine utilizing a waterfall of extra-low head. The two-dimensional Moving Particle Semi-implicit (MPS) method is employed for the simulation. The fluid is discretized by particles, and the flow is computed by the Lagrangian calculation for the particle motion. When the distance between the particles discretizing the waterfall of a width , , is set at , the flow can be simulated with the sufficiently high spatial resolution, and the rotor performance can also be favorably predicted. The present simulation also successfully analyzes the effect of the rotational speed of rotor on the flow and the turbine performance. Tomomi Uchiyama, Haruki Fukuhara, Shouichiro Iio, and Toshihiko Ikeda Copyright © 2013 Tomomi Uchiyama et al. All rights reserved. Design and Performance Evaluation of a Very Low Flow Coefficient Centrifugal Compressor Thu, 14 Nov 2013 08:56:24 +0000 Very low flow coefficient centrifugal compressors are often applied as the last stages of multistage compressors. Due to the lower volume flow rate, the flow channels in the impeller and diffuser are so narrow that friction loss becomes the main factor, which leads to lower efficiency than that of other stages in the same compressors. In addition, most of design methods are generally based on medium flow coefficient centrifugal compressors. Taking on researches on the low flow coefficient centrifugal compressors is significant and necessary. One-dimensional (1D) code, consisting of design and analysis parts, is developed in this study to provide basic geometric data and predict the entire performance of centrifugal compressor. Three-dimensional geometry of the impeller is built. CFD simulation is carried out as well to be compared with 1D prediction. With the continuous geometry adjustment, the final performance of the centrifugal compressor will be fixed once the performance discrepancy between CFD and one-dimensional code is acceptable. The details on the flow field within impeller will be presented through CFD. Yongsheng Wang, Feng Lin, Chaoqun Nie, and Abraham Engeda Copyright © 2013 Yongsheng Wang et al. All rights reserved. Investigation of the Shear Flow Effect and Tip Clearance on a Low Speed Axial Flow Compressor Cascade Mon, 11 Nov 2013 14:46:20 +0000 This paper explores the effect of inlet shear flow on the tip leakage flow in an axial flow compressor cascade. A flow with a high shear rate is generated in the test section of an open circuit cascade wind tunnel by using a combination of screens with a prescribed solidity. It is observed that a stable shear flow of shear rate 1.33 is possible and has a gradual decay rate until 15 times the height of the shear flow generator downstream. The computational results obtained agree well with the available experimental data on the baseline configuration. The detailed numerical analysis shows that the tip clearance improves the blade loading near the tip through the promotion of favorable incidence by the tip leakage flow. The tip clearance shifts the centre of pressure on the blade surface towards the tip. It, however, has no effect on the distribution of end wall loss and deviation angle along the span up to 60% from the hub. In the presence of a shear inflow, the end wall effects are considerable. On the other hand, with a shear inflow, the effects of tip leakage flow are observed to be partly suppressed. The shear flow reduces the tip leakage losses substantially in terms of kinetic energy associated with it. Mahesh Varpe and A. M. Pradeep Copyright © 2013 Mahesh Varpe and A. M. Pradeep. All rights reserved. Design and Parameter Study of a Self-Compensating Hydrostatic Rotary Bearing Wed, 06 Nov 2013 15:44:37 +0000 The influence of design parameters on the static performance of a newly designed self-compensating hydrostatic rotary bearing was investigated. The bearing was designed by incorporating the main attributes of angled-surface self-compensating bearing and opposed-pad self-compensating bearing. A governing model based on flow conservation was built to theoretically study the static performance, and the methodology was validated by experiments. It is pointed out that the influence factors on the bearing static performance are the designed resistance ratio of the restricting land to the bearing land, the inner resistance ratio of the land between pockets to that between the pocket and the drain groove, the initial clearance ratio of the restricting gap to the bearing gap, and the semiconical angle. Their effects on the load carrying capacity and stiffness were investigated by simulation. Results show that the optimum designed resistance ratio is 1; the initial clearance ratio should be small, and the inner resistance ratio should be large. Xiaobo Zuo, Shengyi Li, Ziqiang Yin, and Jianmin Wang Copyright © 2013 Xiaobo Zuo et al. All rights reserved. Evaluation of the Thermal Effects in Tilting Pad Bearing Sat, 02 Nov 2013 13:12:06 +0000 The analysis of thermal effects is of expressive importance in the context of rotordynamics to evaluate the behavior of hydrodynamic bearings because these effects can influence their dynamic characteristics under specific operational conditions. For this reason, a thermohydrodynamic model is developed in this work, in which the pressure distribution in the oil film and the temperature distribution are calculated together. From the pressure distribution, the velocity distribution field is determined, as well as the viscous dissipation, and consequently, the temperature distribution. The finite volume method is applied to solve the Reynolds equation and the energy equation in the thermohydrodynamic model (THD). The results show that the temperature is higher as the rotational speed increases due to the shear rate of the oil film. The maximum temperature in the bearing occurs in the overloaded pad, near the outlet boundary. The experimental tests were performed in a tilting pad journal bearing operating in a steam turbine to validate the model. The comparison between the experimental and numerical results provides a good correlation. The thermohydrodynamic lubrication developed in this assignment is promising to consistently evaluate the behavior of the tilting pad journal bearing operating in relatively high rotational speeds. G. B. Daniel and K. L. Cavalca Copyright © 2013 G. B. Daniel and K. L. Cavalca. All rights reserved. Effect of Dynamic Center Region on the Flow and Mixing Efficiency in a New Tri-Screw Extruder Using 3D Finite Element Modeling Wed, 30 Oct 2013 13:57:37 +0000 Three-dimensional finite element modeling of polymer melt flowing in a new co-rotating tri-screw extruder was established with mesh superposition technique. Based on the particle tracking technology, three typical particle trajectories in the tri-screw extruder were calculated using a 4th-order-Runge-Kutta method to study the dynamic motions of the particles. Then the flow visualizations in the local center region were carried out. Moreover, the dispersive, distributive and stretching mixing efficiencies of the tri-screw and twin-screw extruders were compared, respectively. The results show that when the particles move from one screw to another, there are great abrupt changes in the velocities and displacements, which induce the abrupt change in the stress magnitude. Most of particles, which are initially distributed in the inlet plane of the center region, fast flow out the outlet and don’t pass through any screw. This special phenomenon induces a series of new characteristics in the residence time distribution (RTD), flow number, segregation scale and time averaged efficiency. In comparison with the twin-screw extruder, the tri-screw extruder has better mixing efficiency. X. Z. Zhu, Y. D. He, and G. Wang Copyright © 2013 X. Z. Zhu et al. All rights reserved. Experimental Study on Series Operation of Sliding Vane Pump and Centrifugal Pump Mon, 21 Oct 2013 09:47:53 +0000 A platform for sliding vane pump and centrifugal pump tests is installed to study the series operation of them under different characteristics of pipeline. Firstly, the sliding vane pump and the centrifugal pump work independently, and the performance is recorded. Then, the two types of pumps are combined together, with the sliding vane pump acting as the feeding pump. Comparison is made between the performance of the independently working pump and the performance of series operation pump. Results show that the system flow rate is determined by the sliding vane pump. In order to ensure the stability of the series operation pumping system, the energy consumption required by the pipeline under the system flow should be greater than the pressure energy centrifugal pump can generate. Otherwise, the centrifugal pump can not operate stably, with reflux, swirl, gas-liquid two-phase flow in the runner and strong vibration and noise. The sliding vane pump can be in serial operation with the centrifugal pump under limited conditions. Tao Li, Weiming Zhang, Ming Jiang, and Zhengyang Li Copyright © 2013 Tao Li et al. All rights reserved. Effect of Secondary Flows on Heat Transfer of a Gas Turbine Blade Sun, 20 Oct 2013 14:29:11 +0000 This study presents experimental and numerical investigation for three-dimensional heat transfer characteristics in a turbine blade. An experimental setup was installed with a turbine cascade of five-blade channels. Blade heat transfer measurements were performed for the middle channel under uniform heat flux boundary conditions. Heat was supplied to the blades using twenty-nine electric heating strips cemented vertically on the outer surface of the blades. Distributions of heat transfer coefficient were obtained at three levels through blade height by measuring surface temperature distribution using thermocouples. To understand heat transfer characteristics, surface static pressure distributions on blade surface were also measured. Numerical investigation was performed as well to extend the investigation to locations other than those measured experimentally. Three-dimensional nonisothermal, turbulent flow was obtained by solving Reynolds averaged Navier-Stokes equations and energy equation. The shear stress transport model was employed to represent turbulent flow. It was found through this study that secondary flow generated by flow deflection increases heat transfer coefficient on the blade suction surface. Separation lines with high heat transfer coefficients were predicted numerically with good agreement with the experimental measurements. Hesham M. El-Batsh, Sameh A. Nada, Samia Nasreldin Abdo, and Abdelgalil A. El-Tayesh Copyright © 2013 Hesham M. El-Batsh et al. All rights reserved. Simple and Versatile Dynamic Model of Spherical Roller Bearing Sun, 29 Sep 2013 08:52:18 +0000 Rolling element bearings are essential components of rotating machinery. The spherical roller bearing (SRB) is one variant witnessing increasing use because it is self-aligning and can support high loads. It is becoming increasingly important to understand how the SRB responds dynamically under a variety of conditions. This study introduces a computationally efficient, three-degree-of-freedom, SRB model that was developed to predict the transient dynamic behaviors of a rotor-SRB system. In the model, bearing forces and deflections were calculated as a function of contact deformation and bearing geometry parameters according to the nonlinear Hertzian contact theory. The results reveal how some of the more important parameters, such as diametral clearance, the number of rollers, and osculation number, influence ultimate bearing performance. One pair of calculations looked at bearing displacement with respect to time for two separate arrangements of the caged side-by-side roller arrays, when they are aligned and when they are staggered. As theory suggests, significantly lower displacement variations were predicted for the staggered arrangement. Following model verification, a numerical simulation was carried out successfully for a full rotor-bearing system to demonstrate the application of this newly developed SRB model in a typical real world analysis. Behnam Ghalamchi, Jussi Sopanen, and Aki Mikkola Copyright © 2013 Behnam Ghalamchi et al. All rights reserved. Design Method for Channel Diffusers of Centrifugal Compressors Wed, 18 Sep 2013 09:48:04 +0000 The design method for channel diffusers of centrifugal compressors, which is based on the solving of the inverse problem of gas dynamics, is presented in the paper. The concept of the design is to provide high pressure recovery of the diffuser by assuming the preseparation condition of the boundary layer along one of the channel surfaces. The channel diffuser was designed with the use of developed method to replace the vaned diffuser of the centrifugal compressor model stage. The numerical simulation of the diffusers was implemented by means of CFD software. Obtained gas dynamic characteristics of the designed diffuser were compared to the base vaned diffuser of the compressor stage. Mykola Kalinkevych and Andriy Skoryk Copyright © 2013 Mykola Kalinkevych and Andriy Skoryk. All rights reserved. A New Proposed Return Guide Vane for Compact Multistage Centrifugal Pumps Mon, 19 Aug 2013 10:58:04 +0000 For widely used multistage centrifugal pumps, their former structures are so bulky that nowadays growing interest has been shifted to the development of more compact structures. Following this trend, a compact pump structure is provided and analysed. To maintain the pump’s pressure recovery, as well as to meet the water flow from the impeller, a circumferential twisted return guide vane (RGV) is proposed. To validate this design method, the instantaneous CFD simulations are performed to investigate the rotor-stator interventions. Within the impeller, the pressure fluctuation is cyclic symmetry, where the impeller frequency dominates. At the zone where flow leaves impeller for RGV, the pressure fluctuation is nonperiodic, the impeller frequency is major, and the rotation frequency is secondary. Within RGV, the periodic symmetric fluctuation is recovered, where the rotation frequency is governing. The fluctuation decreases from seven cycles within impeller to two cycles within RGV, indicating that the flow from impeller is well handled by RGV. To examine the pump’s performance, a prototype multistage pump is designed. The testing shows that the pump efficiency is 57.5%, and the stage head is 9 m, which is comparable to former multistage centrifugal pumps. And this design is more advantageous in developing compact multistage centrifugal pumps. Qihua Zhang, Weidong Shi, Yan Xu, Xiongfa Gao, Chuan Wang, Weigang Lu, and Dongqi Ma Copyright © 2013 Qihua Zhang et al. All rights reserved. Characteristics of Centrifugal Pumps Working in Direct or Reverse Mode: Focus on the Unsteady Radial Thrust Sun, 04 Aug 2013 10:16:47 +0000 Experimental and numerical investigations have been carried out to study the behaviour of a centrifugal pump operating in direct mode or turbine mode. First of all, the complete characteristics (head, power, and efficiency) were measured experimentally using a specific test loop. The numerical data obtained from a CFD study performed with the ANSYS CFX software and based on steady state and unsteady approaches were compared to the experimental results. The representation in the 4 operating quadrants shows the various operating zones where the head is always positive. Then, the unsteady radial forces were analysed from transient computations. The results obtained for the pump operation are consistent with the literature and extended to the nonnormal operating conditions, namely, for very high flowrate values. The evolution of the radial load during turbine operation is presented for various partial flow operating points. Anthony Couzinet, Laurent Gros, and Daniel Pierrat Copyright © 2013 Anthony Couzinet et al. All rights reserved. Dynamic Response in Transient Operation of a Variable Geometry Turbine Stage: Influence of the Aerodynamic Performance Mon, 22 Jul 2013 13:46:16 +0000 The transient response of a radial turbine stage with a variable geometry system is evaluated. Mainly, the consequences of the variations of the aerodynamic performance of the stage on the response time are checked. A simple quasi-steady model is derived in order to formalize the expected dependences. Then an experimental campaign is conducted: a brutal step in the feeding conditions of the stage is imposed, and the response time in terms of rotational speed is measured. This has been reproduced on different declinations of the same stage, through the variation of the stator geometry, and correlated to the steady-state performance of the initial and final operating points of the transient phase. The matching between theoretical expectation and results is surprisingly good for some configurations, less for others. The most important factor identified is the mass-flow level during the transient phase. It increases the reactivity, even far above the theoretical expectation for some configurations. For those cases, it is demonstrated that the quasi-steady approach may not be sufficient to explain how the transient response is set. Nicolas Binder, Jaime Garcia Benitez, and Xavier Carbonneau Copyright © 2013 Nicolas Binder et al. All rights reserved. Links between Main Frequencies of Established Rotating Stall and Rotational Frequencies and/or Blade Passing Frequencies Sun, 21 Jul 2013 07:58:07 +0000 The ratios between the main frequency of rotating stall and rotational frequency may be considered in the form of exact ratios of small natural numbers if the pressure signals in compressors during rotating stall include the rotor rotation frequency component. During rotating stall in compressors with good rotor balancing (with absence of the rotational frequency component in the frequency characteristics of pressure signals), these ratios between the main frequency of rotating stall and rotational frequency are or are not in the form of ratios of small natural numbers. The experimentally received characteristics of power spectral density of pressure signals also show the presence of components with combinations of blade passing frequency and different harmonics of main rotating stall frequency. Yeshayahou Levy, Asaf Modelevsky, Joseph Pismenny, Jens Friedrichs, and Detlev Wulff Copyright © 2013 Yeshayahou Levy et al. All rights reserved. Effects of Flow Rate and Viscosity on Slip Factor of Centrifugal Pump Handling Viscous Oils Wed, 10 Jul 2013 11:24:54 +0000 Slip factor is an important parameter in the hydraulic design of centrifugal pump impeller for handling viscous oils. How to extract the factor from CFD computational results and how flow rate and liquid viscosity to affect it remain unclear. In the present paper, the flip factor was estimated by means of two approaches: one is from the velocity triangles at the impeller outlet and the other is due to the impeller theoretical head of 3D turbulent viscous fluid. The velocity of water and viscous oils in the impeller and volute computed by CFD was validated with LDV measurements at the best efficiency point. The effect of exit blade angle on slip factor was clarified. It was shown that the two approaches result into two different slip factors. The factors are significantly dependent of flow rate; however, the liquid viscosity seems to take less effect on them. Volute is responsible for reduction in tangential velocity of liquid at the outlet of impeller at low flow rates. The slip factor of impeller with large exit blade angle is not sensitive to flow rate. Wen-Guang Li Copyright © 2013 Wen-Guang Li. All rights reserved. Numerical Investigations of Unsteady Flow in a Centrifugal Pump with a Vaned Diffuser Tue, 02 Jul 2013 10:29:36 +0000 Computational fluid dynamics (CFD) analyses were made to study the unsteady three-dimensional turbulence in the ERCOFTAC centrifugal pump test case. The simulations were carried out using the OpenFOAM Open Source CFD software. The test case consists of an unshrouded centrifugal impeller with seven blades and a radial vaned diffuser with 12 vanes. A large number of measurements are available in the radial gap between the impeller and the diffuse, making this case ideal for validating numerical methods. Results of steady and unsteady calculations of the flow in the pump are compared with the experimental ones, and four different turbulent models are analyzed. The steady simulation uses the frozen rotor concept, while the unsteady simulation uses a fully resolved sliding grid approach. The comparisons show that the unsteady numerical results accurately predict the unsteadiness of the flow, demonstrating the validity and applicability of that methodology for unsteady incompressible turbomachinery flow computations. The steady approach is less accurate, with an unphysical advection of the impeller wakes, but accurate enough for a crude approximation. The different turbulence models predict the flow at the same level of accuracy, with slightly different results. Olivier Petit and Håkan Nilsson Copyright © 2013 Olivier Petit and Håkan Nilsson. All rights reserved. Performance of Combined Water Turbine with Semielliptic Section of the Savonius Rotor Thu, 30 May 2013 08:36:02 +0000 The Darrieus turbine is a suitable power generation in free stream flow because it is simple in construction, but it has the disadvantage of its small starting torque. The Savonius turbine has a high starting torque but the efficiency is smaller than that of Darrieus turbine. To improve the starting torque of Darrieus turbine, the Savonius buckets are introduced into the Darrieus turbine and the combined turbine is called Darrieus-Savonius turbine. In this study, three semielliptic sections of aspect ratio 0.8 were used for Savonius bucket while the Darrieus blade used three wings of airfoil NACA 0015. The Darrieus-Savonius turbine’s performances were studied experimentally in an irrigation canal of South Sumatera, Indonesia. The results show that the distance of Savonius buckets from the shaft centre influences performance of combined turbine, and the attachment angle of Savonius rotor made important variation of turbine performance. Kaprawi Sahim, Dyos Santoso, and Agus Radentan Copyright © 2013 Kaprawi Sahim et al. All rights reserved. Theoretical Vibration Analysis on 600 Wh Energy Storage Flywheel Rotor—Active Magnetic Bearing System Mon, 20 May 2013 14:41:25 +0000 This paper shows a theoretical vibration analysis regarding the controller’s parameters and the gyroscopic effect, based on a simplified rotordynamic model. Combined with 600 Wh energy storage flywheel rotor system mathematical model, the Campbell diagram of the rotor system was obtained by the calculation of the whirl frequency under different parameters of the controller in MATLAB to analyze the effect of the controller parameter on the whirl frequency and to limit the operating speed and acceleration or deceleration of the rotor. The result of the analysis can be used to set the support position of the rotor system, limit the ratio of transverse moment of inertia and the polar moment of inertia, and direct the flywheel prototype future design. The presented simplified rotordynamic model can also be applied to rotating machines. Jing-na Liu, Zheng-yi Ren, Shan-wei Wu, and Yin-long Tang Copyright © 2013 Jing-na Liu et al. All rights reserved.