scholarly journals Prediction of Relaminarization Effects on Turbine Blade Heat Transfer

2001 ◽  
Author(s):  
R. J. Boyle ◽  
P. W. Giel
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Rotor Blade ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Pressure Gradients ◽  
Pressure Surface ◽  
High Reynolds ◽  
Rotor Shape

An approach to predicting turbine blade heat transfer when turbulent flow relaminarizes due to strong favorable pressure gradients is described. Relaminarization is more likely to occur on the pressure side of a rotor blade. While stators also have strong favorable pressure gradients, the pressure surface is less likely to become turbulent at low to moderate Reynolds numbers. Accounting for the effects of relaminarization for blade heat transfer can substantially reduce the predicted rotor surface heat transfer. This in turn can lead to reduced rotor cooling requirements. Two dimensional midspan Navier-Stokes analyses were done for each of eighteen test cases using eleven different turbulence models. Results showed that including relaminarization effects generally improved the agreement with experimental data. The results of this work indicate that relatively small changes in rotor shape can be utilized to extend the likelihood of relaminarization to high Reynolds numbers. Predictions showing how rotor blade heat transfer at a high Reynolds number can be reduced through relaminarization are given.

Comparisons of Pins/Dimples/Protrusions Cooling Concepts for a Turbine Blade Tip-Wall at High Reynolds Numbers

2010 ◽  
Author(s):  
Gongnan Xie ◽  
Bengt Sunde´n ◽  
Weihong Zhang
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Computational Models ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Gas Leakage ◽  
Leakage Flows ◽  
Blade Tip ◽  
High Reynolds ◽  
The Cost

The blade tip region encounters high thermal loads because of the hot gas leakage flows, and it must therefore be cooled to ensure a long durability and safe operation. A common way to cool a blade tip is to design serpentine passages with 180° turn under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase blade tip lifetime. Pins, dimples and protrusions are well recognized as effective devices to augment heat transfer in various applications. In this paper, enhanced heat transfer of an internal blade tip-wall has been predicted numerically. The computational models consist of a two-pass channel with 180° turn and arrays of circular pins or hemispherical dimples or protrusions internally mounted on the tip-wall. Inlet Reynolds numbers are ranging from 100,000 to 600,000. The overall performance of the two-pass channels is evaluated. Numerical results show that the heat transfer enhancement of the pinned tip is up to a factor of 3.0 higher than that of a smooth tip while the dimpled-tip and protruded-tip provide about 2.0 times higher heat transfer. These augmentations are achieved at the cost of an increase of pressure drop by less than 10%. By comparing the present cooling concepts with pins, dimples and protrusions, it is shown that the pinned-tip exhibit best performance to improve the blade tip cooling. However, when disregarding the added active area and considering the added mechanical stress, it is suggested that the usage of dimples is more suitable to enhance blade tip cooling, especially at low Reynolds numbers.

Detached-Eddy Simulations and Reynolds-Averaged Navier-Stokes Simulations of Delta Wing Vortical Flowfields

2002 ◽  
Vol 124 (4) ◽  
pp. 924-932 ◽  
Author(s):  
Scott Morton ◽  
James Forsythe ◽  
Anthony Mitchell ◽  
David Hajek
Keyword(s):  
Vortex Breakdown ◽  
Delta Wing ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Fighter Aircraft ◽  
Eddy Simulation ◽  
Reynolds Averaged Navier Stokes ◽  
High Reynolds

An understanding of vortical structures and vortex breakdown is essential for the development of highly maneuverable vehicles and high angle of attack flight. This is primarily due to the physical limits these phenomena impose on aircraft and missiles at extreme flight conditions. Demands for more maneuverable air vehicles have pushed the limits of current CFD methods in the high Reynolds number regime. Simulation methods must be able to accurately describe the unsteady, vortical flowfields associated with fighter aircraft at Reynolds numbers more representative of full-scale vehicles. It is the goal of this paper to demonstrate the ability of detached-eddy Simulation (DES), a hybrid Reynolds-averaged Navier-Stokes (RANS)/large-eddy Simulation (LES) method, to accurately predict vortex breakdown at Reynolds numbers above 1×106. Detailed experiments performed at Onera are used to compare simulations utilizing both RANS and DES turbulence models.

How Turbulence Models Perform in Simulating Pipeflow Response to Targeted Wall-Shapes?

2021 ◽  
Author(s):  
Mehran Masoumifar ◽  
Suyash Verma ◽  
Arman Hemmati
Keyword(s):  
Three Dimensional ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Flow Response ◽  
High Reynolds Numbers ◽  
Flow Features ◽  
Rans Models ◽  
Response And Recovery ◽  
High Reynolds

Abstract This study evaluates how Reynolds-Averaged-Navier-Stokes (RANS) models perform in simulating the characteristics of mean three-dimensional perturbed flows in pipes with targeted wall-shapes. Capturing such flow features using turbulence models is still challenging at high Reynolds numbers. The principal objective of this investigation is to evaluate which of the well-established RANS models can best predict the flow response and recovery characteristics in perturbed pipes at moderate and high Reynolds numbers (10000-158000). First, the flow profiles at various axial locations are compared between simulations and experiments. This is followed by assessing the well-known mean pipeflow scaling relations. The good agreement between our computationally predicted data using Standard k-epsilon model and those of experiments indicated that this model can accurately capture the pipeflow characteristics in response to introduced perturbation with smooth sinusoidal axial variations.

scholarly journals Predictions for the Effects of Freestream Turbulence on Turbine Blade Heat Transfer

2004 ◽  
Author(s):  
R. J. Boyle ◽  
Forrest E. Ames ◽  
P. W. Giel
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Steady State ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Pressure Surface ◽  
Wide Range

An approach to predicting the effects of freestream turbulence on turbine vane and blade heat transfer is described. Four models for predicting the effects of freestream turbulence were incorporated into a Navier-Stokes CFD analysis. Predictions were compared with experimental data in order to identify an appropriate model for use across a wide range of flow conditions. The analyses were compared with data from five vane geometries and from four rotor geometries. Each of these nine geometries had data for different Reynolds numbers. Comparisons were made for twenty four cases. Steady state calculations were done because all experimental data were obtained in steady state tests. High turbulence levels often result in suction surface transition upstream of the throat, while at low to moderate Reynolds numbers the pressure surface remains laminar. A two-dimensional analysis was used because the flow is predominantly two-dimensional in the regions where freestream turbulence significantly augments surface heat transfer. Because the evaluation of models for predicting turbulence effects can be affected by other factors, the paper discusses modeling for transition, relaminarization, and near wall damping. Quantitative comparisons are given between the predictions and data.

Heat Transfer to a Pvd Rotor Blade at High Subsonic Passage Throat Mach Numbers

1978 ◽  
Vol 192 (1) ◽  
pp. 225-235 ◽  
Author(s):  
B. W. Martin ◽  
A. Brown ◽  
S. E. Garrett
Keyword(s):  
Heat Transfer ◽  
Rotor Blade ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Pressure Surface ◽  
Air Stream ◽  
Mach Numbers

This paper reports heat-transfer measurements round a PVD rotor blade using a transient method. Instrumented syndanio-asbestos blades forming part of a cascade are suddenly introduced into a heated air stream, the temperature-time response of surface thermocouples attached to copper inserts in the blades then being used to determine local heat-transfer coefficients for (a) passage throat Mach numbers between 0.79 and 0.94 (b) turbulence intensities from 4.15 to 9.05 per cent (c) blade chord Reynolds numbers from 7.8 times 105 to 8.9 times 105. Measured transition lengths on the suction surface, over which the heat transfer nearly trebles, are somewhat short in relation to other measurements. The onset of transition, which is downstream of predictions for the higher Reynolds numbers but accords with the trends of existing correlations, is little influenced by turbulence intensity variations in the above range. Over the pressure surface the heat transfer is less than for a fully-turbulent boundary layer. Comparisons with other high Mach-number measurements suggest that much further work is needed before the effects of scale of turbulence are fully understood.

Effects of Turbulence Intensity and Scale on Turbine Blade Heat Transfer

2015 ◽  
Author(s):  
Robert J. Boyle ◽  
Ali A. Ameri
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Turbulence Intensity ◽  
Film Cooling ◽  
Rotor Blade ◽  
Navier Stokes ◽  
Test Cases ◽  
Freestream Turbulence ◽  
Turbulence Scale

The effects of turbulence intensity and length scale on turbine blade heat transfer and aerodynamic losses are investigated. The importance of freestream turbulence on heat transfer increases with Reynolds number and turbulence intensity, and future turbine blade Reynolds numbers are expected to be higher than in current engines. Even when film cooling is used, accurate knowledge of baseline heat transfer distributions are needed. Heat flux reductions due to film cooling depend on the ratio of film cooled-to-solid blade heat transfer coefficients. Comparisons are made between published experimental data and published correlations for leading edge heat transfer. Stagnation region heat transfer rates of vanes and blades of high pressure turbines can be nearly double those predicted when predictions neglect freestream turbulence effects. Correlations which included the scale of turbulence gave better agreement with data. Two-dimensional Navier-Stokes analysis were done for several existing test cases where measures of the turbulence scale are available. The test cases had significant regions where the flow was not fully turbulent. Freestream turbulence increases laminar heat transfer, but has little influence on turbulent heat transfer. The Navier-Stokes analysis included a model for the effects of high freestream turbulence on laminar or transitioning boundary layers. Comparisons were made with vane and rotor blade data, as well as with high Reynolds number test data that simulated the favorable pressure gradient regions seen in the forward portions of turbine blades. Predictions of surface heat transfer showed the appropriate trends in heat transfer with turbulence intensity and turbulence scale. However, the absolute level of agreement indicated that further verification of approaches to predicting turbulence intensity and scale effects is needed. Significant increases in losses were calculated for vane and rotor blade geometries as inlet turbulence increased.

scholarly journals Two-Equation Turbulence Models for Prediction of Heat Transfer on a Transonic Turbine Blade

2001 ◽  
Author(s):  
Vijay K. Garg ◽  
Ali A. Ameri
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Suction Side ◽  
Navier Stokes ◽  
Production Term ◽  
Passage Vortex ◽  
Sst Model ◽  
Transonic Turbine

Two versions of the two-equation k-ω model and a shear stress transport (SST) model are used in a three-dimensional, multi-block, Navier-Stokes code to compare the detailed heat transfer measurements on a transonic turbine blade. It is found that the SST model resolves the passage vortex better on the suction side of the blade, thus yielding a better comparison with the experimental data than either of the k-ω models. However, the comparison is still deficient on the suction side of the blade. Use of the SST model does require the computation of distance from a wall, which for a multi-block grid, such as in the present case, can be complicated. However, a relatively easy fix for this problem was devised. Also addressed are issues such as (1) computation of the production term in the turbulence equations for aerodynamic applications, and (2) the relation between the computational and experimental values for the turbulence length scale, and its influence on the passage vortex on the suction side of the turbine blade.

Comparisons of Pins/Dimples/Protrusions Cooling Concepts for a Turbine Blade Tip-Wall at High Reynolds Numbers

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
Gongnan Xie ◽  
Bengt Sundén ◽  
Weihong Zhang
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Computational Models ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Gas Leakage ◽  
Leakage Flows ◽  
Blade Tip ◽  
High Reynolds ◽  
The Cost

The blade tip region encounters high thermal loads because of the hot gas leakage flows, and it must therefore be cooled to ensure a long durability and safe operation. A common way to cool a blade tip is to design serpentine passages with a 180 deg turns under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase blade tip lifetime. Pins, dimples, and protrusions are well recognized as effective devices to augment heat transfer in various applications. In this paper, enhanced heat transfer of an internal blade tip-wall has been predicted numerically. The computational models consist of a two-pass channel with 180 deg turn and arrays of circular pins, hemispherical dimples, or protrusions internally mounted on the tip-wall. Inlet Reynolds numbers are ranging from 100,000 to 600,000. The overall performance of the two-pass channels is evaluated. Numerical results show that the heat transfer enhancement of the pinned-tip is up to a factor of 3.0 higher than that of a smooth tip while the dimpled-tip and protruded-tip provide about 2.0 times higher heat transfer. These augmentations are achieved at the cost of an increase of pressure drop by less than 10%. By comparing the present cooling concepts with pins, dimples, and protrusions, it is shown that the pinned-tip exhibits best performance to improve the blade tip cooling. However, when disregarding the added active area and considering the added mechanical stress, it is suggested that the usage of dimples is more suitable to enhance blade tip cooling, especially at low Reynolds numbers.

scholarly journals Navier-Stokes Analysis of Turbine Blade Heat Transfer

1990 ◽  
Author(s):  
R. J. Boyle
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Pressure Gradients ◽  
Freestream Turbulence ◽  
Eddy Viscosity Model ◽  
Experimental Heat ◽  
Experimental Heat Transfer

Comparisons with experimental heat transfer and surface pressures were made for seven turbine vane and blade geometries using a quasi-three-dimensional thin-layer Navier-Stokes analysis. Comparisons are made for cases with both separated and unseparated flow over a range of Reynolds numbers and freestream turbulence intensities. The analysis used a modified Baldwin-Lomax turbulent eddy viscosity model. Modifications were made to account for the effects of: 1) freestream turbulence on both transition and leading edge heat transfer; 2) strong favorable pressure gradients on re-laminarization; and 3) variable turbulent Prandtl number on heat transfer. In addition, the effect on heat transfer of the near-wall model of Deissler is compared with the Van Driest model.

An Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Rectangular Channel With V-Shaped Ribs

2006 ◽  
Author(s):  
Michael Maurer ◽  
Jens von Wolfersdorf ◽  
Michael Gritsch
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
High Reynolds Numbers ◽  
High Reynolds

An experimental and numerical study was conducted to determine the thermal performance of V-shaped ribs in a rectangular channel with an aspect ratio of 2:1. Local heat transfer coefficients were measured using the steady state thermochromic liquid crystal technique. Periodic pressure losses were obtained with pressure taps along the smooth channel sidewall. Reynolds numbers from 95,000 to 500,000 were investigated with V-shaped ribs located on one side or on both sides of the test channel. The rib height-to-hydraulic diameter ratios (e/Dh) were 0.0625 and 0.02, and the rib pitch-to-height ratio (P/e) was 10. In addition, all test cases were investigated numerically. The commercial software FLUENT™ was used with a two-layer k-ε turbulence model. Numerically and experimentally obtained data were compared. It was determined that the heat transfer enhancement based on the heat transfer of a smooth wall levels off for Reynolds numbers over 200,000. The introduction of a second ribbed sidewall slightly increased the heat transfer enhancement whereas the pressure penalty was approximately doubled. Diminishing the rib height at high Reynolds numbers had the disadvantage of a slightly decreased heat transfer enhancement, but benefits in a significantly reduced pressure loss. At high Reynolds numbers small-scale ribs in a one-sided ribbed channel were shown to have the best thermal performance.

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