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.

Heat Transfer in a High Turbulence Air Jet Impinging Over a Flat Circular Disk

2003 ◽  
Vol 125 (2) ◽  
pp. 257-265 ◽  
Author(s):  
Erick A. Siba ◽  
M. Ganesa-Pillai ◽  
Kendall T. Harris ◽  
A. Haji-Sheikh
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Circular Disk ◽  
Stream Velocity ◽  
Wall Jet ◽  
Stagnation Region ◽  
Free Stream Turbulence ◽  
Air Jet

This study concerns the flow and heat transfer characteristics of a turbulent submerged circular air jet impinging on a horizontal flat surface when free stream turbulence exceeds 20 percent. The turbulent fluctuations of the free stream velocity are the primary aerodynamics influencing heat transfer. Two regions with distinct flow characteristics are observed: the stagnation region, and the wall-jet region. According to the linear form of the energy equation, the surface heat flux may be decomposed into laminar and turbulent components. An inverse methodology can determine the turbulent component of the heat transfer coefficient in the stagnation region and in the wall-jet region as a function of the root mean square value of the fluctuating component of velocity in the bulk flow direction.

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.

Influence of Free Stream Turbulence Intensity on Heat Transfer and Flow Around Four In-Line Elliptic Cylinders in Cross Flow

2010 ◽  
Vol 8 (1) ◽  
Author(s):  
Ramadan Y. Sakr ◽  
Nabil M. Berbish ◽  
Ali A. Abd-Aziz
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Average Nusselt Number ◽  
Free Stream ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Elliptic Cylinder ◽  
Major Axis ◽  
Free Stream Turbulence ◽  
Spacing Ratio

The effect of free stream turbulence intensity on heat transfer and flow characteristics around four in-line elliptic cylinders in cross flow was experimentally and numerically investigated. The elliptic cylinders examined had an axis ratio (b/c) of (1:3) with a zero angle of attack (where the major axis is horizontal) and were heated under a constant heat flux condition. Three different sizes of free stream turbulence producing grids (screen) inserted at a distance of 300 mm the upstream test cylinders are used to study the effect of the free stream turbulence. The turbulence intensity levels of 5.6%, 8.3% and 10.5% are obtained from the grid sizes. The effects of cylinder spacing ratio (L/c) were examined within Reynolds number (based on free stream velocity and major axis length) ranging from 3640 to 66240. It was observed that the local and average Nusselt numbers of the tested elliptic cylinders increase with increasing the free stream turbulence intensity. The results showed that the maximum enhancement ratio for the average Nusselt number (for the tested cylinder with grid and for the single elliptic cylinder without grid) was found to be about 1.93 and was obtained for the second elliptic cylinder in four in-line cylinders at L/c=1.5, Re=6150 with free stream turbulence intensity of 10.5%. Also, the flow characteristics varied drastically with both the longitudinal spacing ratio and the inserted grid (screen). Moreover, an empirical correlation for the average Nusselt number of the second elliptic cylinder of the four in-line cylinders was obtained as function of Reynolds number and free stream turbulence intensity.

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.

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