Numerical study of leading-edge heat transfer under free-stream turbulence

2001 ◽  
Author(s):  
Z. Xiong ◽  
S. Lele
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Numerical Study ◽  
Leading Edge ◽  
Free Stream Turbulence

Effect of Elevated Free-Stream Turbulence on Transitional Heat Transfer Over Dual-Scaled Rough Surfaces

2003 ◽  
Author(s):  
Ting Wang ◽  
Matthew C. Rice
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Surface Roughness ◽  
Vortex Shedding ◽  
Free Stream ◽  
Leading Edge ◽  
Test Surface ◽  
Dominant Effect ◽  
Free Stream Turbulence ◽  
Heat Transfer Phenomenon

The surface roughness over a serviced turbine airfoil is usually multi-scaled with varying features that are difficult to be universally characterized. However, it was previously discovered in low freestream turbulence conditions that the height of larger roughness produces separation and vortex shedding, which trigger early transition and exert a dominant effect on flow pattern and heat transfer. The geometry of the roughness and smaller roughness scales played secondary roles. This paper extends the previous study to elevated turbulence conditions with free-stream turbulence intensity ranging from 0.2–6.0 percent. A simplified test condition on a flat plate is conducted with two discrete regions having different surface roughness. The leading edge roughness is comprised of a sandpaper strip or a single cylinder. The downstream surface is either smooth or covered with sandpaper of grit sizes ranging from 100 ∼ 40 (Ra = 37 ∼ 119 μm). Hot wire measurements are conducted in the boundary layer to study the flow structure. The results of this study verify that the height of the largest-scale roughness triggers an earlier transition even under elevated turbulence conditions and exerts a more dominant effect on flow and heat transfer than does the geometry of the roughness. Heat transfer enhancements of about 30 ∼ 40 percent over the entire test surface are observed. The vortical motion, generated by the backward facing step at the joint of two roughness regions, is believed to significantly increase momentum transport across the boundary layer and bring the elevated turbulence from the freestream towards the wall. No such long-lasting heat transfer phenomenon is observed in low FSTI cases even though vortex shedding also exists in the low turbulence cases. The heat transfer enhancement decreases, instead of increases, as the downstream roughness height increases.

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.

scholarly journals Turbulence Intensity, Length Scale, and Heat Transfer Around Stagnation Line of Cylinder and Model Blade

1999 ◽  
Author(s):  
V. P. Maslov ◽  
B. I. Mineev ◽  
K. N. Pichkov ◽  
A. N. Secundov ◽  
A. N. Vorobiev ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Turbulence Models ◽  
Leading Edge ◽  
Circular Cylinders ◽  
Length Scale ◽  
Stagnation Line ◽  
Free Stream Turbulence ◽  
Wide Range

A hot-wire technique was used to measure turbulence characteristics in the vicinity of the stagnation line of circular cylinders and a turbine blade model (a chord length of 1 metre). Heat transfer intensity at the stagnation line of the cylinders was also measured by on-surface probes. The experiments were carried out in a wide range of the Reynolds number based on the blade leading edge/cylinder diameter, D (Re = 2.103–2.106) and integral length scale of free-stream turbulence, Le (Le = 0.1–10D) at two values of free stream turbulence intensity, Tu (Tu = 0.02 and 0.10). Along with the experimental data results of the 2D RANS computations are presented of the flow and heat transfer at the circular cylinder with the use of two turbulence models: a two-equation, k-ω SST, model of Menter, and a new two-equation, ν1-L, model developed in the course of the present study.

Stagnation-point flow under free-stream turbulence

2007 ◽  
Vol 590 ◽  
pp. 1-33 ◽  
Author(s):  
ZHONGMIN XIONG ◽  
SANJIVA K. LELE
Keyword(s):  
Heat Transfer ◽  
Stagnation Point ◽  
Reynolds Stress ◽  
Free Stream ◽  
Leading Edge ◽  
Stagnation Point Flow ◽  
Mean Flow ◽  
Free Stream Turbulence ◽  
Local Boundary ◽  
The Mean

In this paper, the effects of free-stream turbulence on stagnation-point flow and heat transfer are investigated through large eddy simulation (LES) of homogeneous isotropic turbulence impinging upon an isothermal elliptical leading edge. Turbulent mean flow and Reynolds stress profiles along the stagnation streamline, where the mean flow is strain dominant, and at different downstream locations, where the mean flow gradually becomes shear-dominated, are used to characterize evolution of the free-stream turbulence. The Reynolds stress budgets are also obtained, and the turbulence anisotropy is analysed through the balance between the mean flow strain and the velocity pressure gradient correlation. In the presence of free-stream turbulence, intense quasi-streamwise vortices develop near the leading edge with a typical diameter of the order of the local boundary-layer thickness. These strong vortices cause the thermal fluxes to peak at a location much closer to the wall than that of the Reynolds stresses, resulting a greater sensitivity to free-stream turbulence for the heat transfer than the momentum transfer. The heat transfer enhancement obtained by the present LES agrees quantitatively with available experimental measurements. The present LES results are also used to examine the eddy viscosity and pressure-strain correlations in Reynolds stress turbulence models.

THERMAL BARRIER COATING AND TURBULENCE INTENSITY EFFECTS ON LEADING EDGE COOLING USING CONJUGATE HEAT TRANSFER ANALYSIS

2017 ◽  
Vol 41 (2) ◽  
pp. 249-263 ◽  
Author(s):  
Prasert Prapamonthon ◽  
Huazhao Xu ◽  
Zhaoqing Ke ◽  
Wenshuo Yang ◽  
Jianhua Wang
Keyword(s):  
Heat Transfer ◽  
Thermal Barrier Coating ◽  
Conjugate Heat Transfer ◽  
Numerical Study ◽  
Guide Vane ◽  
Leading Edge ◽  
Heat Transfer Analysis ◽  
Thermal Barrier ◽  
Free Stream Turbulence ◽  
Barrier Coating

This is a numerical study of thermal barrier coating (TBC) and turbulence on leading edge (LE) cooling of a guide vane. Numerical results were carried out using 3D CFD with conjugate heat transfer analysis. Important phenomena were revealed. (1) TBC is effective in the LE region especially when free stream turbulence (Tu) increases. (2) At each Tu, TBC near the hub of the vane provides the most effective protection and at the highest Tu, TBC improves overall cooling effectiveness there by about 25%. (3) Near the exits of film hole, TBC may have negative effect, because of heat transfer impedance from the solid structure into the mixing fluid between mainstream and cooling air emitted from film holes.

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.

scholarly journals Navier–Stokes Analysis of Turbine Blade Heat Transfer

1991 ◽  
Vol 113 (3) ◽  
pp. 392-403 ◽  
Author(s):  
R. J. Boyle
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Free Stream 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 free-stream turbulence intensities. The analysis used a modified Baldwin-Lomax turbulent eddy viscosity model. Modifications were made to account for the effects of: (1) free-stream turbulence on both transition and leading edge heat transfer; (2) strong favorable pressure gradients on relaminarizations; 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 Convective Heat Transfer Investigation Around a Film-Cooled Gas Turbine Blade

1990 ◽  
Vol 112 (3) ◽  
pp. 497-503 ◽  
Author(s):  
C. Camci ◽  
T. Arts
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Gas Turbine ◽  
Convective Heat ◽  
Free Stream ◽  
Weight Ratio ◽  
Leading Edge ◽  
Suction Side ◽  
Turbine Rotor ◽  
Free Stream Turbulence

The present paper deals with an experimental convective heat transfer investigation around a film-cooled, high-pressure gas turbine rotor blade mounted in a stationary, linear cascade arrangement. The measurements were performed in the von Karman Institute Isentropic Light Piston Compression Tube facility. The test blade was made of Macor glass ceramic and was instrumented with thin film gages. The coolant flow was ejected simultaneously through the leading edge (three rows of holes), the suction side (two rows of holes), and the pressure side (one row of holes). The effects of overall mass weight ratio, coolant to free-stream temperature ratio, and free-stream turbulence were successively investigated.

Detailed Film Cooling Measurements on a Cylindrical Leading Edge Model: Effect of Free-Stream Turbulence and Coolant Density

1997 ◽  
Author(s):  
Srinath V. Ekkad ◽  
Je-Chin Han ◽  
Hui Du
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Free Stream ◽  
Density Ratio ◽  
Leading Edge ◽  
Cylinder Surface ◽  
Free Stream Turbulence ◽  
Blowing Ratio ◽  
Nusselt Numbers

Detailed heat transfer coefficient and film effectiveness distributions are presented on a cylindrical leading edge model using a transient liquid crystal technique. Tests were done in a low speed wind tunnel on a cylindrical model in a crossflow with two rows of injection holes. Mainstream Reynolds number based on the cylinder diameter was 100,900. The two rows of injection holes were located at ±15° from stagnation. The film holes were spaced 4-hole diameters apart and were angled 30° and 90° to the surface in the spanwise and streamwise directions, respectively. Heat transfer coefficient and film effectiveness distributions are presented on only one side of the front half of the cylinder. The cylinder surface is coated with a thin layer of thermochromic liquid crystals and a transient test is run to obtain the heat transfer coefficients and film effectiveness. Air and CO2 were used as coolant to simulate coolant-to-mainstream density ratio effect. The effect of coolant blowing ratio was studied for blowing ratios of 0.4, 0.8, and 12. Results show that Nusselt numbers downstream of injection increase with an increase in blowing ratio for both coolants. Air provides highest effectiveness at blowing ratio of 0.4 and CO2 provides highest effectiveness at a blowing ratio of 0.8. Higher density coolant (CO2) provides lower Nusselt numbers at all blowing ratios compared to lower density coolant (air). An increase in free-stream turbulence has very small effect on Nusselt numbers for both coolants. However, an increase in free-stream turbulence reduces film effectiveness significantly at low blowing ratios for both coolants.

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