A three-dimensional Navier&#8211;Stokes code has been used to compare the heat transfer coefficient on a film-cooled, rotating turbine blade. The blade chosen is the ACE rotor with five rows containing 93 film cooling holes covering the entire span. This is the only filmcooled rotating blade over which experimental data is available for comparison. Over 2.278 million grid points are used to compute the flow over the blade including the tip clearance region, using Coakley&#39;s <mml:math alttext="$q - \omega$" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>q</mml:mi><mml:mo>&#45;</mml:mo><mml:mi>&#969;</mml:mi></mml:math> turbulence model. Results are also compared with those obtained by Garg and Abhari (1997) using the zero-equation Baldwin-Lomax (B-L)
model. A reasonably good comparison with the experimental data is obtained on the suction
surface for both the turbulence models. At the leading edge, the B-L model yields a better
comparison than the <mml:math alttext="$q - \omega$" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>q</mml:mi><mml:mo>&#45;</mml:mo><mml:mi>&#969;</mml:mi></mml:math> model. On the pressure surface, however, the comparison between
the experimental data and the prediction from either turbulence model is poor. A potential
reason for the discrepancy on the pressure surface could be the presence of unsteady effects due to stator-rotor interaction in the experiments which are not modeled in the present computations. Prediction using the two-equation model is in general poorer than that using the zero-equation model, while the former requires at least 40&#37; more computational resources.

Vijay K. Garg

Heat Transfer on a Film-Cooled Rotating Blade Using a
Two-Equation Turbulence Model

This paper presents a computational procedure for the analysis of steady one-dimensional centrifugal compressor. The numerical model is based on the conservation principles of mass, momentum and energy, and has been utilized to predict the operational and aerodynamic characteristics of a small centrifugal compressor as well as determining the performance and geometry of compressor blades, both straight and curved.

K. A. R. Ismail

C. V. A. G. Rosolen

F. J. Benevenuto

D. Lucato

Small Radial Compressors: Aerodynamic Design and Analysis

Naphthalene sublimation experiments have been conducted to examine the effect of rotation on the regional heat]mass transfer distribution for turbulent air flow in a rotating smooth two-pass square channel that has a 180 turn with sharp corners. The Reynolds number ranges from 5,500 to 14,500 and the rotation number goes up to 0.24. The test channel models the first two passes of serpentine internal cooling passages of gas turbine blades. Flow around a sharp turn causes larger heat]mass transfer increase in the turn and in the second pass than flow around a smooth turn. In the first pass with radially outward flow, rotation increases the heat]mass transfer on the trailing wall and decreases the heat/mass transfer on the leading wall. The reversed trend in the second pass with radially inward flow is evident only after four hydraulic diameters downstream of the turn exit. With rotation, there is an abrupt increase of the regional heat]mass transfer in the upstream portion of the turn on the leading wall. The regional heat]mass transfer on the trailing wall, however, increases along the streamwise direction in the turn, as in the stationary channel case. In the turn and immediately downstream of the turn, the shape of the heat/mass transfer distribution in a rotating channel is invariant over the range of rotation number studied. In a rotating channel, decreasing the Reynolds number increases the heat]mass transfer on the trailing wall and decreases that on the leading wall in the first pass, and increases the heat/mass transfer on both walls in the turn and immediately downstream of the turn.

C. W. Park

M. Kandis

S. C. Lau

Heat/Mass Transfer Distribution in a Rotating Two-Pass Square Channel Part I: Regional Heat Transfer, Smooth Channel

Experiments were performed to study the effect of film hole location on local heat transfer coefficient distribution of a turbine blade model with air or CO2 film injection to simulate coolant density effect. Tests were performed on a five blade linear cascade at the chord Reynolds number of <mml:math alttext="$3 \times 10^5$" id="E1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mn>3</mml:mn><mml:mo>&#xD7;</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mn>5</mml:mn></mml:msup></mml:math> at cascade inlet. The test blade had three rows of film holes in
the leading edge region and two rows each on the pressure and suction surfaces. Film hole
locations were varied by leaving the desired ones open and plugging the rest. A combination
of turbulence grid and unsteady wake was used to generate upstream high turbulence
condition. Results indicate that film injection by itself causes a substantial increase in
Nusselt numbers over a blade model without film holes. An increase in mainstream
turbulence intensity causes an increase in Nusselt numbers over most of the blade surface,
for both coolants, and at all blowing ratios. Film injection promotes an earlier boundary
layer transition on the suction surface and the onset of transition depends on the film
injection location; but at high turbulence levels, transition location is almost independent of
film injection location.

Anant B. Mehendale

H. Wanda Jiang

Srinath V. Ekkad

Je-Chin Han

Effect of Film Injection Location on Local Heat Transfer Coefficient on a Gas Turbine Blade

Cooling of high speed rotating components is a typical situation found in turbomachinery as well as in automobile engines. Accurate knowledge of discharge coefficients and heat transfer of related components is essential for the high performance of the whole engine. This can be achieved by minimized cooling air flows and avoidance of hot spots. In high speed rotating clutches for example aerodynamic investigations improving heat transfer have not been considered in the past. Advanced concepts of modern plate design try to reduce thermal loads by convective cooling methods. Therefore, secondary cooling air flows have to be enhanced by an appropriate design of the rotor stator system with orifices. CFD modelling is used to improve the basic understanding of the flow field in typical geometries used in these systems.The computational results are obtained by a 3-D-finite-volume-code based on body fitted structured grids. The Navier Stokes equations are solved by a pressure-correction method combined with the standard k-e-turbulence model. Considering the rotation of orifices in disks or shafts, the frame of reference has to be changed to the rotating system. The flow through orifices in high speed rotating disks can be calculated with a high level of accuracy in comparison with experiments as shown in Wittig et al. [1994].Numerical results of the flow in a high speed rotating system are presented with emphasis on geometrical variations. Calculations are carried out in order to find an optimum design in terms of position and size of the orifices in the housing. These variations induce different physical phenomena. Special consideration is directed towards the basic problems of the flow through orifices in high speed rotating disks and shafts and the flow inside rotor-stator systems. As expected, the very complex flow fields are dominated by rotational effects. In addition it is shown that differences occur between the configuration of optimized mass flow rate and the geometry with a maximum of total heat transfer. Obviously, optimization procedures are dependent on the knowledge of the local flow field and cannot be performed without advanced CFD-methods. It is demonstrated that the approach presented here is suitable for these tasks.

S. Wittig

S. Kim

Th. Scherer

I. Weissert

Numerical Study for Optimizing Heat Transfer in High
Speed Rotating Components

The vortex model of propellers is modified and applied to the high-speed horizontal axis turbines. The turbine blades are replaced by lifting lines and trailing vortices which shed along the blade span. The model is not a free wake model, but it is still a nonlinear one which should be solved iteratively. In addition to the regular case where the trailing vortices are constrained to distribute along a helical surface, another version, where each trailing vortex sheding from the blade grows as a free helical vortex line, is also included. Performance parameters are calculated by application of the Biot-Savart law along with the Kutta-Joukowski theorem. Predictions are, shown to compare favorably with existing numerical data from more involved free wake methods, but require less computational effort. Thereby, the present method may be a very useful tool for calculating the aerodynamic loads on horizontal-axis wind turbine blades.

Horia  Dumitrescu

Vladimir  Cardos

Wind Turbine Aerodynamic Performance
by Lifting Line Method

This paper illustrates the relative merits of using Natural Laminar Flow (NLF) airfoils in the design of Vertical Axis Wind Turbines (VAWT). This is achieved by the application of the double-multiple-streamtube model of Paraschivoiu to the performance predictions of VAWTs equipped with conventional and NLF blades. Furthermore, in order to clearly illustrate the potential benefit of reducing the drag, the individual contributions of lift and drag to power are presented. The dynamic-stall phenomena are modelled using the method of Gormont as modified by several researchers. Among the various implementations of this dynamic-stall model available in the literature, the most appropriate and general for NLF applications has been identified through detailed comparisons between predicted performances and experimental data. This selection process is presented in the paper. It has been demonstrated that the use ofNLF airfoils in VAWT applications can lead to significant improvements with respect to conventional design only in a very low wind speed range, the extent of which is negligible with respect to the VAWT operational wind speeds.

Christian Masson

Christophe Leclerc

Ion Paraschivoiu

Appropriate Dynamic-Stall Models for Performance
Predictions of VAWTs with NLF Blades

The mass transfer (analogous to heat transfer) and pressure loss characteristics of staggered short pin-fin arrays are investigated experimentally in the range of Reynolds number 3000 to 18,000 based on fin diameter and mean approach-flow velocity. Three different shapes of fins with aspect ratio of 2 are examined: one uniform-diameter circular fin (UDCF) and two stepped-diameter circular fins (SDCF1 and SDCF2). Flow visualization using oil-lampblack reveals complex flow characteristics associated with the repeated production of horseshoe vortices and fin wakes, and the interactions among these. The SDCF1 and SDCF2 arrays show flow characteristics different from the UDCF array due to downflow from the steps. For all arrays tested, the near-endwall flow varies row by row in the initial rows until it reaches a stable pattern after the third row. The row-averaged Sherwood numbers obtained from the naphthalene sublimation experiment also show a row-by-row variation pattern similar to the flow results. While the SDCF2 array has the highest mass transfer rate, the SDCF1 array has the smallest pressure loss at the same approach-flow velocity. The fin surfaces have higher array-averaged Sherwood number than the endwall and the ratio between these changes with fin shape and Reynolds number. The performance of the pin-fin arrays is analyzed under two different constraints: the mass[heat transfer rate at fixed pumping power, and the mass/heat transfer area and pressure loss to fulfill fixed heat load at a fixed mass flow rate. In both cases, the SDCF2 array shows the best performance.

R. J. Goldstein

S. B. Chen

Flow and Mass Transfer Performance in Short Pin-Fin
Channels with Different Fin Shapes

Naphthalene sublimation technique and the heat/mass transfer analogy are used to determine the detailed local heat/mass transfer distributions on the leading and trailing walls of a twopass square channel with smooth walls that rotates about a perpendicular axis. Since the variation of density is small in the flow through the channel, buoyancy effect is negligible. Results show that, in both the stationary and rotating channel cases, very large spanwise variations of the mass transfer exist in he turn and in the region immediately downstream of the turn in the second straight pass. In the first straight pass, the rotation-induced Coriolis forces reduce the mass transfer on the leading wall and increase the mass transfer on the trailing wall. In the turn, rotation significantly increases the mass transfer on the leading wall, especially in the upstream half of the turn. Rotation also increases the mass transfer on the trailing wall, more in the downstream half of the turn than in the upstream half of the turn. Immediately downstream of the turn, rotation causes the mass transfer to be much higher on the trailing wall near the downstream corner of the tip of the inner wall than on the opposite leading wall. The mass transfer in the second pass is higher on the leading wall than on the trailing wall. A slower flow causes higher mass transfer enhancement in the turn on both the leading and trailing walls.

R. T. Kukreja

Heat (Mass) Transfer in a Rotating Two-Pass Square Channel &#x2014; Part II:
Local Transfer Coefficient, Smooth Channel

About this journal

International Journal of Rotating Machinery publishes original research articles as well as review articles on all types of rotating machinery employing gas, vapor, particle, liquid, and their mixtures (including slurry) as the working substances.

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Chief Editor, Professor Amano, is based at the University of Wisconsin–Milwaukee and his research concentrates on the enhancement of energy production using wind, biomass, alternate fuels, and fossil energy sources.

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International Journal of Rotating Machinery - Table of contents 1998

International Journal of Rotating Machinery | Hindawi

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International Journal of Rotating Machinery publishes original research articles as well as review articles on all types of rotating machinery employing gas, vapor, particle, liquid, and their mixtures (including slurry) as the working substances.

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International Journal of Rotating Machinery

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International Journal of Rotating Machinery