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.

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 Direct numerical simulation of heat transfer from the stagnation region of a heated cylinder affected by an impinging wake

2011 ◽  
Vol 669 ◽  
pp. 64-89 ◽  
Author(s):  
JAN G. WISSINK ◽  
WOLFGANG RODI
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Three Dimensional ◽  
Stream Velocity ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Vortical Structures ◽  
Free Stream Turbulence ◽  
Heated Cylinder ◽  
Three Dimensional Simulations

The effect of an incoming wake on the flow around and heat transfer from the stagnation region of a circular cylinder was studied using direct numerical simulations (DNSs). Four simulations were carried out at a Reynolds number (based on free-stream velocity and cylinder diameterD) ofReD= 13200: one two-dimensional (baseline) simulation and three three-dimensional simulations. The three-dimensional simulations comprised a baseline simulation with a uniform incoming velocity field, a simulation in which realistic wake data – generated in a separate precursor DNS – were introduced at the inflow plane and, finally, a simulation in which the turbulent fluctuations were removed from the incoming wake in order to study the effect of the mean velocity deficit on the heat transfer in the stagnation region. In the simulation with realistic wake data, the incoming wake still exhibited the characteristic meandering behaviour of a near-wake. When approaching the regions immediately above and below the stagnation line of the cylinder, the vortical structures from the wake were found to be significantly stretched by the strongly accelerating wall-parallel (circumferential) flow into elongated vortex tubes that became increasingly aligned with the direction of flow. As the elongated streamwise vortical structures impinge on the stagnation region, on one side they transport cool fluid towards the heated cylinder, while on the other side hot fluid is transported away from the cylinder towards the free stream, thereby increasing the heat transfer. The DNS results are compared with various semi-empirical correlations for predicting the augmentation of heat transfer due to free-stream turbulence.

Effects of Free-Stream Turbulence on the Instantaneous Heat Transfer in a Wall Jet Flow

1997 ◽  
Vol 119 (2) ◽  
pp. 359-363 ◽  
Author(s):  
S. Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Flow Direction ◽  
Vertical Direction ◽  
Jet Flow ◽  
Wall Jet ◽  
Axial Component ◽  
Free Stream Turbulence ◽  
Wall Jet Flow ◽  
Hot Film

This is a preliminary study in order to understand how free-stream turbulence increases heat transfer. Effects of free-stream turbulence on instantaneous heat transfer were investigated in a wall jet flow. Heat transfer traces obtained by a hot-film probe flush-mounted with the surface showed an intermittent structure with definite peaks at certain time intervals. The number of peaks per unit time increased with increasing turbulence intensity. A wall jet test rig was designed and built. The initial thickness and the velocity of the wall jet were 10 cm and 24.4 m/s, respectively. The hot-film probe, which was flush with the surfaces, was positioned at 10 cm intervals on the surface in the flow direction. The profiles of mean velocity and axial component of the Reynolds stress were measured with a horizontal hot-wire probe. Space correlation coefficients for u′ and q′ were obtained in the vertical direction to the wall. This paper concentrates on the effects of turbulence level on instantaneous heat transfer at the wall. It is speculated that the intermittent structures of the heat transfer traces are related to burst phenomena and increase in heat transfer is due to increased ejections (bursts) at the wall with increasing turbulence levels.

scholarly journals Effects of Free Stream Turbulence on the Instantaneous Heat Transfer in a Wall Jet Flow

1995 ◽  
Author(s):  
Savash Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Flow Direction ◽  
Vertical Direction ◽  
Jet Flow ◽  
Wall Jet ◽  
Axial Component ◽  
Free Stream Turbulence ◽  
Wall Jet Flow ◽  
Hot Film

This is a preliminary study in order to understand how free stream turbulence increases the heat transfer. Effects of free stream turbulence on the instantaneous heat transfer were investigated in a wall jet flow. Heat transfer traces obtained by a hot film probe flush-mounted with the surface showed an intermittent structure with definite peaks at certain time intervals. Number of peaks per unit time increased with increasing turbulence intensity. A wall jet test rig was designed and built. The initial thickness and the velocity of the wall jet were 10 cm and 24.4 m/s respectively. The hot film probe which was flush with the surfaces was positioned at 10 cm intervals on the surface in the flow direction. The profiles of mean velocity and axial component of the Reynolds stress were measured with a horizontal hot wire probe. Space correlation coefficients for u′ and q′ were obtained in the vertical direction to the wall. This paper concentrates on the effects of turbulence level on the instantaneous heat transfer at the wall. It is speculated that intermittent structure of the heat transfer traces are related to burst phenomena and increase in heat transfer is due to increased ejections (bursts) at the wall with increasing turbulence levels.

Influence of Free-Stream Turbulence on Turbulent Boundary Layer Heat Transfer and Mean Profile Development, Part I—Experimental Data

1983 ◽  
Vol 105 (1) ◽  
pp. 33-40 ◽  
Author(s):  
M. F. Blair
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layer Flow ◽  
Free Stream ◽  
Full Range ◽  
Stream Velocity ◽  
Free Stream Turbulence ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

An experimental research program was conducted to determine the influence of free-stream turbulence on zero pressure gradient, fully turbulent boundary layer flow. Connective heat transfer coefficients and boundary layer mean velocity and temperature profile data were obtained for a constant free-stream velocity of 30 m/s and free-stream turbulence intensities ranging from approximately 1/4 to 7 percent. Free-stream multicomponent turbulence intensity, longitudinal integral scale, and spectral distributions were obtained for the full range of turbulence levels. The test results with 1/4 percent free-stream turbulence indicate that these data were in excellent agreement with classic two-dimensional, low free-stream turbulence, turbulent boundary layer correlations. For fully turbulent boundary layer flow, both the skin friction and heat transfer were found to be substantially increased (up to ∼ 20 percent) for the higher levels of free-stream turbulence. Detailed results of the experimental study are presented in the present paper (Part I). A comprehensive analysis is provided in a companion paper (Part II).

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 The Turbulence That Matters

1997 ◽  
Author(s):  
R. E. Mayle ◽  
K. Dullenkopf ◽  
A. Schulz
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Gas Turbines ◽  
Free Stream ◽  
Transitional Flow ◽  
Stream Velocity ◽  
Length Scale ◽  
Effective Frequency ◽  
Large Wave ◽  
Free Stream Turbulence

A unified expression for the spectrum of turbulence is developed by asymptotically matching known expressions for small and large wave numbers, and a formula for the one-dimensional spectral function which depends on the turbulence Reynolds number Reλ is provided. In addition, formulas relating all the length scales of turbulence are provided. These relations also depend on Reynolds number. The effects of free-stream turbulence on laminar heat transfer and pre-transitional flow in gas turbines are re-examined in light of these new expressions using our recent thoughts on an ‘effective’ frequency of turbulence and an ‘effective’ turbulence level. The results of this are that the frequency most effective for laminar heat transfer is about 1.3U/Le, where U is the free-stream velocity and Le is the length scale of the eddies containing the most turbulent energy, and the most effective frequency for producing pre-transitional boundary layer fluctuations is about 0.3U/η where η is Kolmogorov’s length scale. In addition, the role of turbulence Reynolds number on stagnation heat transfer and transition is discussed, and new expressions to account for its effect are provided.

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.

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