EFFECTS OF FREE STREAM TURBULENCE INTENSITY AND INTEGRAL LENGTH SCALE ON HEAT TRANSFER FROM A CIRCULAR CYLINDER IN CROSSFLOW

1982 ◽  
Author(s):  
Rama Subba Reddy Gorla ◽  
Noel Nemeth
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Integral Length Scale ◽  
Length Scale ◽  
Free Stream Turbulence

scholarly journals Measurements of the Influence of Integral Length Scale on Stagnation Region Heat Transfer

1997 ◽  
Vol 3 (2) ◽  
pp. 117-132 ◽  
Author(s):  
G. James Van Fossen ◽  
Chan Y. Ching
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Leading Edge ◽  
Integral Length Scale ◽  
Width Ratio ◽  
Length Scale ◽  
Grid Data ◽  
Stagnation Region ◽  
Free Stream Turbulence

The purpose of the present work was twofold: first, to determine if a length scale existed that would cause the greatest augmentation in stagnation region heat transfer for a given turbulence intensity and second, to develop a prediction tool for stagnation heat transfer in the presence of free stream turbulence. Toward this end, a model with a circular leading edge was fabricated with heat transfer gages in the stagnation region. The model was qualified in a low turbulence wind tunnel by comparing measurements with Frossling's solution for stagnation region heat transfer in a laminar free stream. Five turbulence generating grids were fabricated; four were square mesh, biplane grids made from square bars. Each had identical mesh to bar width ratio but different bar widths. The fifth grid was an array of fine parallel wires that were perpendicular to the axis of the cylindrical leading edge. Turbulence intensity and integral length scale were measured as a function of distance from the grids. Stagnation region heat transfer was measured at various distances downstream of each grid. Data were taken at cylinder Reynolds numbers ranging from 42,000 to 193,000. Turbulence intensities were in the range 1.1 to 15.9 percent while the ratio of integral length scale to cylinder diameter ranged from 0.05 to 0.30. Stagnation region heat transfer augmentation increased with decreasing length scale. An optimum scale was not found. A correlation was developed that fit heat transfer data for the square bar grids to within ±4%. The data from the array of wires were not predicted by the correlation; augmentation was higher for this case indicating that the degree of isotropy in the turbulent flow field has a large effect on stagnation heat transfer. The data of other researchers are also compared with the correlation.

Free-Stream Turbulence From a Circular Wall Jet on a Flat Plate Heat Transfer and Boundary Layer Flow

1989 ◽  
Vol 111 (1) ◽  
pp. 78-86 ◽  
Author(s):  
R. MacMullin ◽  
W. Elrod ◽  
R. Rivir
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Flow Characteristics ◽  
Surface Profile ◽  
Constant Heat Flux ◽  
Length Scale ◽  
Wall Jet ◽  
Reynolds Analogy ◽  
Free Stream Turbulence

The effects of the longitudinal turbulence intensity parameter of free-stream turbulence (FST) on heat transfer were studied using the aggressive flow characteristics of a circular tangential wall jet over a constant heat flux surface. Profile measurements of velocity, temperature, integral length scale, and spectra were obtained at downstream locations (2 to 20 x/D) and turbulence intensities (7 to 18 percent). The results indicated that the Stanton number (St) and friction factor (Cf) increased with increasing turbulence intensity. The Reynolds analogy factor (2St/Cf) increased up to turbulence intensities of 12 percent, then became constant, and decreased after 15 percent. This factor was also found to be dependent on the Reynolds number (Rex) and plate configuration. The influence of length scale, as found by previous researchers, was inconclusive at the conditions tested.

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.

Free-Stream Turbulence Effects on Film Cooling With Shaped Holes

2003 ◽  
Vol 125 (1) ◽  
pp. 65-73 ◽  
Author(s):  
Christian Saumweber ◽  
Achmed Schulz ◽  
Sigmar Wittig
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Free Stream ◽  
Operating Conditions ◽  
Integral Length Scale ◽  
Length Scale ◽  
Free Stream Turbulence ◽  
Blowing Ratio ◽  
Cylindrical Holes ◽  
The Impact

A comprehensive set of generic experiments has been conducted to investigate the effect of elevated free-stream turbulence on film cooling performance of shaped holes. A row of three cylindrical holes as a reference case, and two rows of holes with expanded exits, a fanshaped (expanded in lateral direction), and a laidback fanshaped hole (expanded in lateral and streamwise direction) have been employed. With an external (hot gas) Mach number of Mam=0.3 operating conditions are varied in terms of free-stream turbulence intensity (up to 11%), integral length scale at constant turbulence intensity (up to 3.5 hole inlet diameters), and blowing ratio. The temperature ratio is fixed at 0.59 leading to an enginelike density ratio of 1.7. The results indicate that shaped and cylindrical holes exhibit very different reactions to elevated free-stream turbulence levels. For cylindrical holes film cooling effectiveness is reduced with increased turbulence level at low blowing ratios whereas a small gain in effectiveness can be observed at high blowing ratios. For shaped holes, increased turbulence intensity is detrimental even for the largest blowing ratio M=2.5. In comparison to the impact of turbulence intensity the effect of varying the integral length scale is found to be of minor importance. Finally, the effect of elevated free-stream turbulence in terms of heat transfer coefficients was found to be much more pronounced for the shaped holes.

Effect of Free-Stream Turbulence on Heat Transfer and Fluid Flow in a Transonic Turbine Stage

2006 ◽  
Author(s):  
F. Mumic ◽  
B. Sunden
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Turbulence Intensity ◽  
Rotational Speed ◽  
Free Stream ◽  
Length Scale ◽  
Turbine Stage ◽  
Free Stream Turbulence ◽  
Turbulence Length ◽  
Turbulence Length Scale

In the present work, a numerical study has been performed to simulate the effect of free-stream turbulence, length scale and variations in rotational speed of the rotor on heat transfer and fluid flow for a transonic high-pressure turbine stage with tip clearance. The stator and rotor rows interact via a mixing plane, which allows the stage to be computed in a steady manner. The focus is on turbine aerodynamics and heat transfer behavior at the mid-span location, and at the rotor tip and casing region. The results of the fully 3D CFD simulations are compared with experimental results available for the so-called MT1 turbine stage. The predicted heat transfer and static pressure distributions show reasonable agreement with the experimental data. In general, the local Nusselt number increases, at the same turbulence length scale, as the turbulence intensity increases, and the location of the suction side boundary layer transition moves upstream towards the blade leading edge. Comparison of the different length scales at the same turbulence intensity shows that the stagnation heat transfer was significantly increased as the length scale increased. However, the length scale evidenced no significant effects on blade tip or rotor casing heat transfer. Also, the results presented in this paper show that the rotational speed in addition to the turbulence intensity and length scale has an important contribution to the turbine blade aerodynamics and heat transfer.

Free-Stream Turbulence Effects on Film Cooling With Shaped Holes

2002 ◽  
Author(s):  
Christian Saumweber ◽  
Achmed Schulz ◽  
Sigmar Wittig
Keyword(s):  
Turbulence Intensity ◽  
Film Cooling ◽  
Free Stream ◽  
Operating Conditions ◽  
Integral Length Scale ◽  
Length Scale ◽  
Free Stream Turbulence ◽  
Blowing Ratio ◽  
Cylindrical Holes ◽  
The Impact

A comprehensive set of generic experiments has been conducted to investigate the effect of elevated free-stream turbulence on film cooling performance of shaped holes. A row of three cylindrical holes as a reference case, and two rows of holes with expanded exits, a fanshaped (expanded in lateral direction), and a laidback fanshaped hole (expanded in lateral and streamwise direction) have been employed. With an external (hot gas) Mach number of Mam = 0.3 operating conditions are varied in terms of free-stream turbulence intensity (up to 11%), integral length scale at constant turbulence intensity (up to 3.5 hole inlet diameters), and blowing ratio. The temperature ratio is fixed at 0.59 leading to an engine-like density ratio of 1.7. The results indicate that shaped and cylindrical holes exhibit very different reactions to elevated free-stream turbulence levels. For cylindrical holes film cooling effectiveness is reduced with increased turbulence level at low blowing ratios whereas a small gain in effectiveness can be observed at high blowing ratios. For shaped holes, increased turbulence intensity is detrimental even for the largest blowing ratio (M = 2.5). In comparison to the impact of turbulence intensity the effect of varying the integral length scale is found to be of minor importance. Finally the effect of elevated free-stream turbulence in terms of heat transfer coefficients was found to be much more pronounced for the shaped holes.

Sign in / Sign up

Export Citation Format

Share Document