Enhanced Heat Transfer and Shear Stress Due to High Free-Stream Turbulence

1995 ◽  
Vol 117 (3) ◽  
pp. 418-424 ◽  
Author(s):  
K. A. Thole ◽  
D. G. Bogard
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Skin Friction ◽  
Free Stream ◽  
Surface Heat ◽  
Wall Region ◽  
Transfer Enhancement ◽  
Enhanced Heat Transfer ◽  
Free Stream Turbulence ◽  
Wall Interaction

Surface heat transfer and skin friction enhancements, as a result of free-stream turbulence levels between 10 percent < Tu > 20 percent, have been measured and compared in terms of correlations given throughout the literature. The results indicate that for this range of turbulence levels, the skin friction and heat transfer enhancements scale best using parameters that are a function of turbulence level and dissipation length scale. However, as turbulence levels approach Tu = 20 percent, the St′ parameter becomes more applicable and simpler to apply. As indicated by the measured rms velocity profiles, the maximum streamwise rms value in the near-wall region, which is needed for St′, is the same as that measured in the free stream at Tu = 20 percent. Analogous to St′, a new parameter, Cf′, was found to scale the skin friction data. Independent of all the correlations evaluated, the available data show that the heat transfer enhancement is greater than the enhancement of skin friction with increasing turbulence levels. At turbulence levels above Tu = 10 percent, the free-stream turbulence starts to penetrate the boundary layer and inactive motions begin replacing shear-stress producing motions that are associated with the fluid/wall interaction. Although inactive motions do not contribute to the shear stress, these motions are still active in removing heat.

Enhanced Heat Transfer and Shear Stress due to High Freestream Turbulence

1994 ◽  
Author(s):  
K. A. Thole ◽  
D. G. Bogard
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Skin Friction ◽  
Surface Heat ◽  
Wall Region ◽  
Turbulence Level ◽  
Freestream Turbulence ◽  
Transfer Enhancement ◽  
Enhanced Heat Transfer ◽  
Wall Interaction

Surface heat transfer and skin friction enhancements, as a result of freestream turbulence levels between 10% < Tu < 20%, have been measured and compared in terms of correlations given throughout the literature. The results indicate that for this range of turbulence levels, the skin friction and heat transfer enhancements scale best using parameters which are a function of turbulence level and dissipation length scale. However, as turbulence levels approach Tu = 20%, the St′ parameter becomes more applicable and simpler to apply. As indicated by the measured rms velocity profiles, the maximum streamwise rms value in the near-wall region, which is needed for St′, is the same as that measured in the freestream at Tu = 20%. Analogous to St′, a new parameter, Cf, was found to scale the skin friction data. Independent of all the correlations evaluated, the available data show that the heat transfer enhancement is greater than enhancements of skin friction with increasing turbulence levels. At turbulence levels above Tu = 10%, the freestream turbulence starts to penetrate the boundary layer and inactive motions begin replacing shear-stress producing motions that are associated with the fluid/wall interaction. Although inactive motions do not contribute to the shear stress, these motions are still active in removing heat.

scholarly journals Comparison of k-ε Models in Predicting Heat Transfer and Skin Friction Under High Free Stream Turbulence

1996 ◽  
Author(s):  
Ganesh R. Iyer ◽  
Savash Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boundary Layer ◽  
Skin Friction ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Skin Friction Coefficient ◽  
Empirical Correlations ◽  
Free Stream Turbulence ◽  
Boundary Layer Equations

Calculations of the effects of high free stream turbulence (FST) on heat transfer and skin friction in a flat plate turbulent boundary layer using different k-ε models (Launder-Sharma, K-Y Chien, Lam-Bremhorsi and Jones-Launder) are presented. This study was carried out in order to investigate the prediction capabilities of these models under high FST conditions. In doing so, TEXSTAN, a partial differential equation solver which is based on the ideas of Patankar and Spalding and solves steady-flow boundary layer equations, was used. Firstly, these models were compared as to how they predicted very low FST (≤ 1% turbulence intensity) cases. These baseline cases were tested by comparing predictions with both experimental data and empirical correlations. Then, these models were used in order to determine the effect of high FST (>5% turbulence intensity) on heat transfer and skin friction and compared with experimental data. Predictions for heat transfer and skin friction coefficient for all the turbulence intensities tested by all the models agreed well (within 1–8%) with experimental data. However, all these models predicted poorly the dissipation of turbulent kinetic energy (TKE) in the free stream and TKE profiles. Physical reasoning as to why the aforementioned models differ in their predictions and the probable cause of poor prediction of free-stream TKE and TKE profiles are given.

Effects of Rotation on Blade Surface Heat Transfer: An Experimental Investigation

1998 ◽  
Vol 120 (3) ◽  
pp. 530-540 ◽  
Author(s):  
R. W. Moss ◽  
R. W. Ainsworth ◽  
T. Garside
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Free Stream ◽  
Time History ◽  
Surface Heat ◽  
Blade Surface ◽  
Surface Heat Transfer ◽  
Free Stream Turbulence ◽  
Effects Of Rotation ◽  
Wake Passing

Measurements of turbine blade surface heat transfer in a transient rotor facility are compared with predictions and equivalent cascade data. The rotating measurements involved both forward and reverse rotation (wake-free) experiments. The use of thin-film gages in the Oxford Rotor Facility provides both time-mean heat transfer levels and the unsteady time history. The time-mean level is not significantly affected by turbulence in the wake; this contrasts with the cascade response to free-stream turbulence and simulated wake passing. Heat transfer predictions show the extent to which such phenomena are successfully modeled by a time-steady code. The accurate prediction of transition is seen to be crucial if useful predictions are to be obtained.

Influence of Free-Stream Turbulence on Turbulent Boundary Layer Heat Transfer and Mean Profile Development, Part II—Analysis of Results

1983 ◽  
Vol 105 (1) ◽  
pp. 41-47 ◽  
Author(s):  
M. F. Blair
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Skin Friction ◽  
Free Stream ◽  
Distribution Data ◽  
Stream Velocity ◽  
Mean Velocity ◽  
Reynolds Analogy ◽  
Free Stream Turbulence

An experimental research program was conducted to determine the influence of free-stream turbulence on zero pressure gradient, fully turbulent boundary layer flow. In Part I of this paper, convective heat transfer coefficients, boundary layer mean velocity and temperature profile data, as well as wall skin friction coefficient distribution data were presented for five flow conditions of constant free-stream velocity (30 m/s) and free-stream turbulence intensities ranging from approximately 1/4 to 7 percent. These data indicated that the turbulence had significant effects on both the turbulent boundary layer skin friction and heat transfer. In the current paper, these new data are compared to various independent experimental data and analytical correlations of free-stream turbulence effects. This analysis has shown that the effects documented in Part I were a function of the freestream turbulence intensity, the turbulence length scale, and the boundary layer momentum thickness Reynolds number. In addition, the Reynolds analogy factor (2St/cf) was shown to increase by just over 1 percent for each 1 percent increase in free-stream turbulence level. New correlations for the influence of free-stream turbulence on skin friction, heat transfer, and the Reynolds analogy factor are presented.

An analysis of flow and heat transfer in separated flows over blocked surface

2012 ◽  
Vol 227 (3) ◽  
pp. 481-491
Author(s):  
O Yemenici ◽  
ZA Firatoglu
Keyword(s):  
Heat Transfer ◽  
Turbulent Flows ◽  
Free Stream ◽  
Separated Flows ◽  
Stream Velocity ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Free Stream Turbulence ◽  
Intensity Measurements ◽  
Flow And Heat Transfer

The flow and heat transfer characteristics of flat and blocked surfaces were experimentally examined under the influence of the free stream velocity of 3, 5, 10 and 15 m/s encompassing laminar, transitional and turbulent flows. A constant-temperature hot wire anemometer was used for the velocity and turbulent intensity measurements, and copper-constant thermocouples and a micro-manometer for temperature and static pressures measurements, respectively. The flow over blocked surface separated in front of the first block and attached on it, then circulated between blocks, and then reattached behind the last block. The results showed that the flow separation before the first block occurred earlier in laminar–laminar separated–reattached flow than the transitional and turbulent flows and turbulent–turbulent separated–reattached flow leading to a shorter reattachment region with high free-stream turbulence. The presence of the separation and reattachment caused the heat transfer enhancement, which was more pronounced in the laminar flow and new empirical equations were developed for the local Stanton numbers.

Sign in / Sign up

Export Citation Format

Share Document