Prediction of Heat Transfer in a Ribbed Channel: Evaluation of Unsteady RANS Methodology

2005 ◽  
Author(s):  
William D. York ◽  
D. Scott Holloway ◽  
James H. Leylek
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Reynolds Stress ◽  
Flow Direction ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Stress Model ◽  
Clemson University ◽  
Ribbed Channel ◽  
Closure Models

Heat transfer in a straight channel with rib turbulators on one wall is predicted numerically with an unsteady Reynolds-averaged Navier-Stokes (URANS) methodology and compared to code-validation quality experimental data from the literature. Additionally, for comparison, steady simulations of the problem are conducted using two popular turbulence closure models, a Realizable k-ε model and a differential Reynolds-stress model. Closure in the URANS simulation is provided by a new eddy-viscosity-based model that was developed in the Advanced Computational Research Laboratory at Clemson University. This new model consists of three transport equations, and it is designed specifically to promote natural unsteadiness in the flow without the need for artificial forcing. In all cases, the Reynolds number, based on hydraulic diameter, is equal to 24,000. Eight square ribs, orthogonal to the flow direction, are equally spaced on the bottom wall of the channel. For the URANS simulation, after the flow becomes fully-developed in the streamwise direction, the predicted Nusselt number on the ribbed wall follows the trend of measured data from the modeled experimental study. However, the unsteady simulation slightly overpredicts the distance to the peak heat transfer aft of each rib. Also, the heat transfer prediction is very dependent on the grid resolution aft of the ribs. Therefore, efficient refinement of the unstructured mesh and grid-independence issues are discussed. Results of both steady simulations show a significant underprediction of Nusselt number over the entire ribbed wall, with the Reynolds-stress model giving the better result of the two steady closure models. The results of this study clearly show that unsteady vortex shedding off of the ribs is important in the physics of this problem, and a systematic, unsteady methodology is necessary to accurately predict ribbed-channel heat transfer.

Numerical Simulation of Flow and Heat Transfer Past a Turbine Blade With a Squealer-Tip

2002 ◽  
Author(s):  
Huitao Yang ◽  
Sumanta Acharya ◽  
Srinath V. Ekkad ◽  
Chander Prakash ◽  
Ron Bunker
Keyword(s):  
Heat Transfer ◽  
Reynolds Stress ◽  
Pressure Ratio ◽  
Reynolds Stress Model ◽  
Leakage Flow ◽  
Stress Model ◽  
Tip Leakage Flow ◽  
Transfer Coefficients ◽  
Model Calculations ◽  
Flow And Heat Transfer

Numerical calculations are performed to simulate the tip leakage flow and heat transfer on the squealer (recessed) tip of GE-E3 turbine rotor blade. A squealer tip with a 3.77% recess of the blade span is considered in this study, and the results are compared with the predictions for a flat-tip blade. The calculations have been performed for an isothermal blade with an overall pressure ratio of 1.32, an inlet turbulence intensity of 6.1%, and for three different tip gap clearances of 1%, 1.5% and 2.5% of the blade span. These conditions correspond to the experiments reported by Azad et al. [1]. The calculations have been performed for three different turbulence models (the standard high Re k-ε model, the RNG k-ε and the Reynolds Stress Model) in order to assess the capability of the models in correctly predicting the blade heat transfer. The predictions show good agreement with the experimental data, with the Reynolds stress model calculations clearly providing the best results. Substantial reductions in the tip heat transfer and leakage flow is obtained with the squealer tip configuration. With the squealer tip, the heat transfer coefficients on the shroud and on the suction surface of the blade are also considerably reduced.

scholarly journals Rotating Flow and Heat Transfer in Cylindrical Cavities With Radial Inflow

2012 ◽  
Author(s):  
B. G. Vinod Kumar ◽  
John W. Chew ◽  
Nicholas J. Hills
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Stress ◽  
Integral Method ◽  
Eddy Viscosity ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Rotating Disc ◽  
Flow And Heat Transfer ◽  
Viscosity Models

Design and optimization of an efficient internal air system of a gas turbine requires thorough understanding of the flow and heat transfer in rotating disc cavities. The present study is devoted to numerical modelling of flow and heat transfer in a cylindrical cavity with radial inflow and comparison with the available experimental data. The simulations are carried out with axi-symmetric and 3-D sector models for various inlet swirl and rotational Reynolds numbers upto 2.1×106. The pressure coefficients and Nusselt numbers are compared with the available experimental data and integral method solutions. Two popular eddy viscosity models, the Spalart-Allmaras and the k-ε, and a Reynolds stress model have been used. For cases with particularly strong vortex behaviour the eddy viscosity models show some shortcomings with the Spalart-Allmaras model giving slightly better results than the k-ε model. Use of the Reynolds stress model improved the agreement with measurements for such cases. The integral method results are also found to agree well with the measurements.

scholarly journals Computation of Turbulent Heat Transfer on the Walls of a 180 Degree Turn Channel With a Low Reynolds Number Reynolds Stress Model

2002 ◽  
Author(s):  
D. L. Rigby ◽  
A. A. Ameri ◽  
E. Steinthorsson
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Reynolds Stress ◽  
Low Reynolds Number ◽  
Reynolds Stress Model ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Stress Model ◽  
Generalized Gradient ◽  
Low Reynolds

The Low Reynolds number version of the Stress-ω model and the two equation k-ω model of Wilcox were used for the calculation of turbulent heat transfer in a 180 degree turn simulating an internal coolant passage. The Stress-ω model was chosen for its robustness. The turbulent thermal fluxes were calculated by modifying and using the Generalized Gradient Diffusion Hypothesis. The results showed that using this Reynolds Stress model allowed better prediction of heat transfer compared to the k-ω two equation model. This improvement however required a finer grid and commensurately more CPU time.

A Numerical Study of Vortex Breakdown in Turbulent Swirling Flows

1999 ◽  
Vol 122 (1) ◽  
pp. 179-183 ◽  
Author(s):  
Robert E. Spall ◽  
Blake M. Ashby
Keyword(s):  
Reynolds Stress ◽  
Stokes Equations ◽  
Vortex Breakdown ◽  
Numerical Study ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Stress Model ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
The Mean

Solutions to the incompressible Reynolds-averaged Navier–Stokes equations have been obtained for turbulent vortex breakdown within a slightly diverging tube. Inlet boundary conditions were derived from available experimental data for the mean flow and turbulence kinetic energy. The performance of both two-equation and full differential Reynolds stress models was evaluated. Axisymmetric results revealed that the initiation of vortex breakdown was reasonably well predicted by the differential Reynolds stress model. However, the standard K-ε model failed to predict the occurrence of breakdown. The differential Reynolds stress model also predicted satisfactorily the mean azimuthal and axial velocity profiles downstream of the breakdown, whereas results using the K-ε model were unsatisfactory. [S0098-2202(00)01601-1]

Application of Reynolds-Stress Transport Models to Stern and Wake Flows

1995 ◽  
Vol 39 (04) ◽  
pp. 263-283 ◽  
Author(s):  
F. Sotiropoulos ◽  
V. C. Patel
Keyword(s):  
Reynolds Stress ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Reynolds Stress Model ◽  
Equation Model ◽  
Navier Stokes ◽  
Tensor Model ◽  
Stress Model ◽  
Wake Flows ◽  
Flow Features

ABSTRACT The Reynolds-averaged Navier-Stokes equations are solved to assess the importance of the turbulence model in the prediction of ship stern and wake flows. Solutions are obtained with a two-equation scalar turbulence model and a seven-equation Reynolds-stress tensor model, both of which resolve the flow up to the wall, holding invariant all aspects of the numerical method, including solution domain, initial and boundary conditions, and grid topology and density. Calculations are carried out for two tanker forms used as test cases at recent workshops, and solutions are compared with each other and with experimental data. The comparisons reveal that the Reynolds-stress model accurately predicts most of the experimentally observed flow features in the stern and near-wake regions whereas the two-equation model predicts only the overall qualitative trends. In particular, solutions with the Reynolds-stress model clarify the origin of the stern vortex.

Flow and Heat Transfer Predictions for a Flat-Tip Turbine Blade

2002 ◽  
Author(s):  
Huitao Yang ◽  
Sumanta Acharya ◽  
Srinath V. Ekkad ◽  
Chander Prakash ◽  
Ron Bunker
Keyword(s):  
Heat Transfer ◽  
Reynolds Stress ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Computational Effort ◽  
Stress Model ◽  
Tip Leakage Flow ◽  
Flow And Heat Transfer ◽  
Pitch Direction ◽  
Blade Tip

Numerical calculations are performed to simulate the tip leakage flow and heat transfer on the GE-E3 High-Pressure-Turbine (HPT) rotor blade. The calculations are performed for a single blade with periodic conditions imposed along the two boundaries in the circumferential-pitch direction. Cases considered are a flat blade tip at three different tip gap clearances of 1%, 1.5% and 2.5% of the blade span. The numerical results are obtained for two different pressure ratios (ratio of inlet total pressure to exit static pressure) of 1.2 and 1.32 and an inlet turbulence level of 6.1%. To explore the effect of turbulence models on the heat transfer results, three different models of increasing complexity and computational effort (standard high Re k-ε model, RNG k-ε and Reynolds Stress Model) are investigated. The predicted tip heat transfer results are compared with the experimental data of Azad [1], and show satisfactory agreement with the data. Hear transfer predictions for all three turbulence models are comparable, and no significant improvements are obtained with the Reynolds-stress model.

Aerothermal Characterization of a Rotating Ribbed Channel at Engine Representative Conditions: Part II — Detailed LCT Measurements

2015 ◽  
Author(s):  
Ignacio Mayo ◽  
Aude Lahalle ◽  
Gian Luca Gori ◽  
Tony Arts
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cross Section ◽  
Flow Direction ◽  
Channel Cross Section ◽  
Wall Region ◽  
Static Case ◽  
Ribbed Channel ◽  
Static Conditions

The present two-part work deals with a detailed characterization of the flow field and heat transfer distribution in a model of a rotating ribbed channel performed in a novel setup which allows test conditions at high Rotation numbers (Ro). The tested model is mounted on a rotating frame with all the required instrumentation, resulting in a high spatial resolution and accuracy. The channel has a cross section with an aspect ratio of 0.9 and a ribbed wall with 8 ribs perpendicular to the main flow direction. The blockage of the ribs is 10% of the channel cross section, whereas the rib pitch to height ratio is 10. In this second part of the study, the heat transfer distribution over the wall region between the 6th and 7th ribs is obtained by means of Liquid Crystal Thermography (LCT). Tests were firstly carried out at a Reynolds number of 15000 and a maximum Ro of 1.00 to evaluate the evolution of the heat transfer with increasing rotation. On the trailing side, the overall Nusselt number increases with rotation until a limit value a 50% higher than in the static case, which is achieved after a value of the Rotation number of about 0.3. On the leading side, the overall Nusselt number decreases with increasing rotation speed to reach a minimum which is approximately 50% of the one found in static conditions. The velocity measurements at Re=15000 and Ro=0.77 provided in Part I of this paper are finally merged to provide a consistent explanation of the heat transfer distribution in this model. Moreover, heat transfer measurements were performed at Reynolds numbers of 30000 and 55000, showing approximately the same trend.

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