Effect of Free-Stream Turbulence on Heat Transfer through a Turbulent Boundary Layer

1978 ◽  
Vol 100 (4) ◽  
pp. 671-677 ◽  
Author(s):  
J. C. Simonich ◽  
P. Bradshaw
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Skin Friction Coefficient ◽  
Reynolds Analogy ◽  
Low Reynolds Numbers ◽  
Free Stream Turbulence ◽  
High Reynolds

Measurements in a boundary layer in zero pressure gradient show that the effect of grid-generated free-stream turbulence is to increase heat transfer by about five percent for each one percent rms increase of the longitudinal intensity. In fact, even a Reynolds analogy factor, 2 × (Stanton number)/(skin-friction coefficient), increases significantly. It is suggested that the irreconcilable differences between previous measurements are attributable mainly to the low Reynolds numbers of most of those measurements. The present measurements attained a momentum-thickness Reynolds number of 6500 (chord Reynolds number approximately 6.3 × 106) and are thought to be typical of high-Reynolds-number flows.

Effects of Reynolds Number and Free-Stream Turbulence on Boundary Layer Transition in a Compressor Cascade

2000 ◽  
Author(s):  
Heinz-Adolf Schreiber ◽  
Wolfgang Steinert ◽  
Bernhard Küsters
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Bypass Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
High Reynolds Numbers ◽  
High Turbulence ◽  
High Reynolds

An experimental and analytical study has been performed on the effect of Reynolds number and free-stream turbulence on boundary layer transition location on the suction surface of a controlled diffusion airfoil (CDA). The experiments were conducted in a rectilinear cascade facility at Reynolds numbers between 0.7 and 3.0×106 and turbulence intensities from about 0.7 to 4%. An oil streak technique and liquid crystal coatings were used to visualize the boundary layer state. For small turbulence levels and all Reynolds numbers tested the accelerated front portion of the blade is laminar and transition occurs within a laminar separation bubble shortly after the maximum velocity near 35–40% of chord. For high turbulence levels (Tu > 3%) and high Reynolds numbers transition propagates upstream into the accelerated front portion of the CDA blade. For those conditions, the sensitivity to surface roughness increases considerably and at Tu = 4% bypass transition is observed near 7–10% of chord. Experimental results are compared to theoretical predictions using the transition model which is implemented in the MISES code of Youngren and Drela. Overall the results indicate that early bypass transition at high turbulence levels must alter the profile velocity distribution for compressor blades that are designed and optimized for high Reynolds numbers.

Temperature Control of Blow-Down, Supersonic Tunnels

1956 ◽  
Vol 60 (541) ◽  
pp. 67-70
Author(s):  
T. A. Thomson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Reynolds Numbers ◽  
Stagnation Temperature ◽  
Blow Down ◽  
High Reynolds Numbers ◽  
Experimental Errors ◽  
High Reynolds

The blow-down type of intermittent, supersonic tunnel is attractive because of its simplicity and because relatively high Reynolds numbers can be obtained for a given size of test section. An adverse characteristic, however, is the fall of stagnation temperature during runs, which can affect experiments in several ways. The Reynolds number varies and the absolute velocity is not constant, even if the Mach number and pressure are; heat-transfer cannot be studied under controlled conditions and the experimental errors arising from the effect of heat-transfer on the boundary layer vary in time. These effects can become significant in quantitative experiments if the tunnel is large and the variation of temperature very rapid; the expense required to eliminate them might then be justified.

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.

A Study of the Relationship Between Free-Stream Turbulence and Stagnation Region Heat Transfer

1987 ◽  
Vol 109 (1) ◽  
pp. 10-15 ◽  
Author(s):  
G. J. VanFossen ◽  
R. J. Simoneau
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Free Stream ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Cylinder Surface ◽  
Nasa Lewis Research ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Free Stream Turbulence

A study has been conducted at the NASA Lewis Research Center to investigate the mechanism that causes free-stream turbulence to increase heat transfer in the stagnation region of turbine vanes and blades. The work was conducted in a wind tunnel at atmospheric conditions to facilitate measurements of turbulence and heat transfer. The model size was scaled up to simulate Reynolds numbers (based on leading edge diameter) that are to be expected on a turbine blade leading edge. Reynolds numbers from 13,000 to 177,000 were run in the present tests. Spanwise averaged heat transfer measurements with high and low turbulence have been made with “rough” and smooth surface stagnation regions. Results of these measurements show that, at the Reynolds numbers tested, the boundary layer remained laminar in character even in the presence of free-stream turbulence. If roughness was added the boundary layer became transitional as evidenced by the heat transfer increase with increasing distance from the stagnation line. Hot-wire measurements near the stagnation region downstream of an array of parallel wires has shown that vorticity in the form of mean velocity gradients is amplified as flow approaches the stagnation region. Finally smoke wire flow visualization and liquid crystal surface heat transfer visualization were combined to show that, in the wake of an array of parallel wires, heat transfer was a minimum in the wire wakes where the fluctuating component of velocity (local turbulence) was the highest. Heat transfer was found to be the highest between pairs of vortices where the induced velocity was toward the cylinder surface.

Measurements in a Turbine Cascade Flow Under Ultra Low Reynolds Number Conditions

2001 ◽  
Vol 124 (1) ◽  
pp. 100-106 ◽  
Author(s):  
Kenneth W. Van Treuren ◽  
Terrence Simon ◽  
Marc von Koller ◽  
Aaron R. Byerley ◽  
James W. Baughn ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Vortex Generators ◽  
Separation Region ◽  
Suction Surface ◽  
Low Reynolds Numbers ◽  
Free Stream Turbulence ◽  
Low Reynolds

With the new generation of gas turbine engines, low Reynolds number flows have become increasingly important. Designers must properly account for transition from laminar to turbulent flow and separation of the flow from the suction surface, which is strongly dependent upon transition. Of interest to industry are Reynolds numbers based upon suction surface length and flow exit velocity below 150,000 and as low as 25,000. In this paper, the extreme low end of this Reynolds number range is documented by way of pressure distributions, loss coefficients, and identification of separation zones. Reynolds numbers of 25,000 and 50,000 and with 1 percent and 8-9 percent turbulence intensity of the approach flow (free-stream turbulence intensity, FSTI) were investigated. At 25,000 Reynolds number and low FSTI, the suction surface displayed a strong and steady separation region. Raising the turbulence intensity resulted in a very unsteady separation region of nearly the same size on the suction surface. Vortex generators were added to the suction surface, but they appeared to do very little at this Reynolds number. At the higher Reynolds number of 50,000, the low-FSTI case was strongly separated on the downstream portion of the suction surface. The separation zone was eliminated when the turbulence level was increased to 8-9 percent. Vortex generators were added to the suction surface of the low-FSTI case. In this instance, the vortices were able to provide the mixing needed to re-establish flow attachment. This paper shows that massive separation at very low Reynolds numbers (25,000) is persistent, in spite of elevated FSTI and added vortices. However, at a higher Reynolds number, there is opportunity for flow reattachment either with elevated free-stream turbulence or with added vortices. This may be the first documentation of flow behavior at such low Reynolds numbers. Although it is undesirable to operate under these conditions, it is important to know what to expect and how performance may be improved if such conditions are unavoidable.

scholarly journals Preliminary Results of a Study of the Relationship Between Free Stream Turbulence and Stagnation Region Heat Transfer

1985 ◽  
Author(s):  
G. James VanFossen ◽  
Robert J. Simoneau
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Free Stream ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Nasa Lewis Research ◽  
Hot Wire ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Free Stream Turbulence

A study is being conducted at the NASA Lewis Research Center to investigate the mechanism that causes free stream turbulence to increase heat transfer in the stagnation region of turbine vanes and blades. The work is being conducted in a wind tunnel at atmospheric conditions to facilitate measurements of turbulence and heat transfer. The model size is scaled up to simulate Reynolds numbers (based on leading edge diameter) that are to be expected on a turbine blade leading edge. Reynolds numbers from 13 000 to 177 000 were run in the present tests. Spanwise averaged heat transfer measurements with high and low turbulence have been made with “rough” and smooth surface stagnation regions. Results of these measurements show that the boundary layer remains laminar in character even in the presence of free stream turbulence at the Reynolds numbers tested. If roughness is added the boundary layer becomes transitional as evidenced by the heat transfer increase with increasing distance from the stagnation line. Hot wire measurements near the stagnation region downstream of an array of parallel wires has shown that vorticity in the form of mean velocity gradients is amplified as flow approaches the stagnation region. Circumferential traverses of a hot wire probe very near the surface of the cylinder have shown the fluctuating component of velocity changes in character depending on free stream turbulence and Reynolds number. Finally smoke wire flow visualization and liquid crystal surface heat transfer visualization have been combined to show that, in the wake of an array of parallel wires, heat transfer is a minimum in the wire wakes where the fluctuating component of velocity (local turbulence) was the highest. Heat transfer was found to be the highest between pairs of vortices where the induced velocity is toward the cylinder surface.

Effects of Reynolds Number and Free-Stream Turbulence on Boundary Layer Transition in a Compressor Cascade

2000 ◽  
Vol 124 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Heinz-Adolf Schreiber ◽  
Wolfgang Steinert ◽  
Bernhard Ku¨sters
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Bypass Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
High Reynolds Numbers ◽  
High Turbulence ◽  
High Reynolds

An experimental and analytical study has been performed on the effect of Reynolds number and free-stream turbulence on boundary layer transition location on the suction surface of a controlled diffusion airfoil (CDA). The experiments were conducted in a rectilinear cascade facility at Reynolds numbers between 0.7 and 3.0×106 and turbulence intensities from about 0.7 to 4 percent. An oil streak technique and liquid crystal coatings were used to visualize the boundary layer state. For small turbulence levels and all Reynolds numbers tested, the accelerated front portion of the blade is laminar and transition occurs within a laminar separation bubble shortly after the maximum velocity near 35–40 percent of chord. For high turbulence levels (Tu>3 percent) and high Reynolds numbers, the transition region moves upstream into the accelerated front portion of the CDA blade. For those conditions, the sensitivity to surface roughness increases considerably; at Tu=4 percent, bypass transition is observed near 7–10 percent of chord. Experimental results are compared to theoretical predictions using the transition model, which is implemented in the MISES code of Youngren and Drela. Overall, the results indicate that early bypass transition at high turbulence levels must alter the profile velocity distribution for compressor blades that are designed and optimized for high Reynolds numbers.

A New Low-Reynolds Number k-ε Model for Simulation of Momentum and Heat Transport Under High Free Stream Turbulence

1998 ◽  
Author(s):  
Ganesh R. Iyer ◽  
Savash Yavuzkurt
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Friction Coefficient ◽  
Skin Friction ◽  
Free Stream ◽  
Low Reynolds Number ◽  
Skin Friction Coefficient ◽  
Stanton Number ◽  
Data Set ◽  
Free Stream Turbulence

A modified low-Reynolds number k-ε model for predicting effects of high free stream turbulence (FST) on transport of momentum and heat in a flat plate turbulent boundary layer is presented. An additional production term incorporating the effects of FST intensity (velocity scale) was included in the TKE equation. The constant cμ in the equation for the transport coefficient μt was modified using empirical information. These modifications were applied to two well tested k-ε models (Launder-Sharma and K-Y Chien,) under high FST conditions (initial FST intensity, Tui > 5%). Models were implemented in a two-dimensional boundary layer code. The high FST data sets against which the predictions (in the turbulent region) were compared had initial FST intensities of 6.53% and 25.7%. In a previous paper, it was shown that predictions of the original models became poorer (overprediction upto more than 50% for skin friction coefficient and Stanton number, and underprediction of turbulent kinetic energy (TKE) upto more than 50%) as FST increased to about 26%. In comparison, the new model developed here provided excellent results for TKE in the boundary layer when compared to the data set with Tui = 6.53%. Results for skin friction coefficient and Stanton number were also very good (within 2% of mean experimental data). For the case of data set with Tui = 25.7%, results of skin friction coefficient, Stanton number and TKE have also vastly improved, but still have scope for more improvement. The present model incorporates physics of free stream turbulence in turbulence modeling and provides a new method for simulating flows with high FST. Future work will focus on including length scale effects in the current model to obtain better predictions for the higher intensity case (Tui = 25.7%) and simulate flows typical in gas turbine engine environments.

scholarly journals Modelling high Reynolds number wall–turbulence interactions in laboratory experiments using large-scale free-stream turbulence

2017 ◽  
Vol 375 (2089) ◽  
pp. 20160091 ◽  
Author(s):  
Eda Dogan ◽  
R. Jason Hearst ◽  
Bharathram Ganapathisubramani
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Boundary Layers ◽  
High Reynolds Number ◽  
Free Stream ◽  
Wall Turbulence ◽  
Scale Interactions ◽  
Free Stream Turbulence ◽  
High Reynolds

A turbulent boundary layer subjected to free-stream turbulence is investigated in order to ascertain the scale interactions that dominate the near-wall region. The results are discussed in relation to a canonical high Reynolds number turbulent boundary layer because previous studies have reported considerable similarities between these two flows. Measurements were acquired simultaneously from four hot wires mounted to a rake which was traversed through the boundary layer. Particular focus is given to two main features of both canonical high Reynolds number boundary layers and boundary layers subjected to free-stream turbulence: (i) the footprint of the large scales in the logarithmic region on the near-wall small scales, specifically the modulating interaction between these scales, and (ii) the phase difference in amplitude modulation. The potential for a turbulent boundary layer subjected to free-stream turbulence to ‘simulate’ high Reynolds number wall–turbulence interactions is discussed. The results of this study have encouraging implications for future investigations of the fundamental scale interactions that take place in high Reynolds number flows as it demonstrates that these can be achieved at typical laboratory scales. This article is part of the themed issue ‘Toward the development of high-fidelity models of wall turbulence at large Reynolds number’.

A Model for Diffusion of Turbulent Kinetic Energy for Calculation of Momentum and Heat Transfer in High FST Flows

2002 ◽  
Author(s):  
Savas Yavuzkurt ◽  
Ganesh R. Iyer
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boundary Layer ◽  
Friction Coefficient ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Free Stream ◽  
Skin Friction Coefficient ◽  
Data Sets ◽  
Free Stream Turbulence

A modified low-Reynolds number k-ε model (named YI-diffn. model) for predicting effects of high free stream turbulence (FST) on momentum transport and heat transfer in a flat plate turbulent boundary layer is presented. An additional turbulent kinetic energy (TKE) diffusion term incorporating the effects of FST intensity (velocity scale) and length scale was included in the TKE equation. This model was developed with experience from many years of experimental and theoretical studies in the area of high FST flows. The constant cμ in the equation for the transport coefficient μt was modified using experimental data. These modifications were applied to a well-tested k-ε model (K-Y Chien called KYC in this study) under high FST conditions (initial FST intensity, Tui > 5%). Models were implemented in a 2-D boundary layer code. The high FST zero pressure gradient data sets against which the predictions (in the turbulent region) were compared had initial FST intensities of 6.53% and 25.7%. In a previous paper, it was shown that predictions of the original k-ε models became poorer (over prediction up to more than 50% for skin friction coefficient and Stanton number, and under prediction of TKE up to more than 50%) as FST increased to about 26%. In comparison, the new model developed here provided excellent results (within ±3% of experimental data) for skin friction coefficient and Stanton number for both the data sets. TKE results were excellent for Tui = 6.53%, but have scope for improvement in the case of Tui = 25.7%. The present model incorporates physics of transport of free stream turbulence in turbulence modeling and provides a new method for simulating flows with high FST. Future work will focus upon improving the model further and applying it to practical applications like flow over gas turbine blades.

Sign in / Sign up

Export Citation Format

Share Document