Stagnation-Point Heat Transfer: The Effect of the First Damko¨hler Similarity Parameter

1972 ◽  
Vol 94 (4) ◽  
pp. 410-414 ◽  
Author(s):  
A. Alkidas ◽  
P. Durbetaki
Keyword(s):  
Heat Transfer ◽  
Blunt Body ◽  
Combustible Mixture ◽  
Surface Heat ◽  
Arrhenius Law ◽  
Governing Equations ◽  
Similarity Parameter ◽  
Stagnation Region ◽  
Kinetics Of ◽  
Temperature Surface

The present study considers the heat interaction between a combustible mixture and a constant-temperature surface near the stagnation region of a blunt body. The steady-state governing equations have been solved numerically for the case of Le = 1. A second-order Arrhenius law is assumed to describe the chemical kinetics of the mixture. The first Damko¨hler similarity parameter is shown to critically influence the surface heat transfer. The parameter represents a measure of the convective time to the chemical time.

The Influence of Large-Scale High-Intensity Turbulence on Vane Heat Transfer

1997 ◽  
Vol 119 (1) ◽  
pp. 23-30 ◽  
Author(s):  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
High Intensity ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Surface Heat ◽  
Grid Turbulence ◽  
Stagnation Region ◽  
Linear Cascade ◽  
Pressure Surface ◽  
Scale Turbulence

An experimental research program was undertaken to examine the influence of large-scale high-intensity turbulence on vane heat transfer. The experiment was conducted in a four-vane linear cascade at exit Reynolds numbers of 500,000 and 800,000 based on chord length. Heat transfer measurements were made for four inlet turbulence conditions including a low turbulence case (Tu ≅ 1 percent), a grid turbulence case (Tu ≅ 7.5 percent), and two levels of large-scale turbulence generated with a mock combustor at two upstream locations (Tu ≅ 12 percent and 8 percent). The heat transfer data demonstrated that the length scale, Lu, has a significant effect on stagnation region and pressure surface heat transfer.

Influence of High Mainstream Turbulence on Leading Edge Film Cooling Heat Transfer

1992 ◽  
Vol 114 (4) ◽  
pp. 707-715 ◽  
Author(s):  
A. B. Mehendale ◽  
J. C. Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Blunt Body ◽  
Leading Edge ◽  
Surface Heat ◽  
Blowing Ratio ◽  
Turbulence Effect ◽  
The Heat Transfer Coefficient

The influence of high mainstream turbulence on leading edge film effectiveness and heat transfer coefficient was studied. High mainstream turbulence was produced by a passive grid and a jet grid. Experiments were performed using a blunt body with a semicylinder leading edge with a flat afterbody. The mainstream Reynolds number based on leading edge diameter was about 100,000. Spanwise and streamwise distributions of film effectiveness and heat transfer coefficient in the leading edge and on the flat sidewall were obtained for three blowing ratios, through rows of holes located at ±15 and ±40 deg from stagnation. The holes in each row were spaced three hole diameters apart and were angled 30 and 90 deg to the surface in the spanwise and streamwise directions, respectively. The results indicate that the film effectiveness decreases with increasing blowing ratio, but the reverse is true for the heat transfer coefficient. The leading edge film effectiveness for low blowing ratio (B = 0.4) is significantly reduced by high mainstream turbulence (Tu = 9.67 and 12.9 percent). The mainstream turbulence effect is diminished in the leading edge for higher blowing ratios (B = 0.8 and 1.2) but still exists on the flat sidewall region. Also, the leading edge heat transfer coefficient for blowing ratio of 0.8 increases with increasing mainstream turbulence; but the effect for other blowing ratios [B = 0.4 and 1.2) is not as systematic as for B = 0.8. Surface heat load is significantly reduced with leading edge film cooling.

Roughness-induced turbulent wedges in a hypersonic blunt-body boundary layer

2014 ◽  
Vol 754 ◽  
pp. 208-231 ◽  
Author(s):  
A. Fiala ◽  
R. Hillier ◽  
D. Estruch-Samper
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Laminar Flow ◽  
Boundary Layer Thickness ◽  
Blunt Body ◽  
Roughness Element ◽  
Surface Heat ◽  
Hypersonic Boundary Layer ◽  
Element Size ◽  
Body Boundary

AbstractThis paper uses measurements of surface heat transfer to study roughness-induced turbulent wedges in a hypersonic boundary layer on a blunt cylinder. A family of wedges was produced by changing the height of an isolated roughness element, providing conditions in the following range: fully effective tripping, for the largest element, with a turbulent wedge forming immediately downstream of the element; a long wake, in length several hundred times the boundary layer thickness, leading ultimately to transition; and retention of laminar flow, for the smallest element. With appropriate element size, a fully intermittent wedge formed, comprising a clear train of turbulent spots.

Influence of High Mainstream Turbulence on Leading Edge Film Cooling Heat Transfer

1990 ◽  
Author(s):  
A. B. Mehendale ◽  
J. C. Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Blunt Body ◽  
Leading Edge ◽  
Surface Heat ◽  
Blowing Ratio ◽  
Turbulence Effect ◽  
The Heat Transfer Coefficient

The influence of high mainstream turbulence on leading edge film effectiveness and heat transfer coefficient was studied. High mainstream turbulence was produced by a passive grid and a jet grid. Experiments were performed using a blunt body with a semi-cylinder leading edge with a flat afterbody. The mainstream Reynolds number based on leading edge diameter was about 100,000. Spanwise and streamwise distributions of film effectiveness and heat transfer in the leading edge and on the flat sidewall were obtained for three blowing ratios, through rows of holes located at ±15° and ±40° from stagnation. The holes in each row were spaced three hole-diameters apart and were angled 30° and 90° to the surface in the spanwise and streamwise directions respectively. The results indicate that the film effectiveness decreases with increasing blowing ratio, but the reverse is true for the heat transfer coefficient. The leading edge film effectiveness for low blowing ratio (B = 0.4) is significantly reduced by high mainstream turbulence (Tu = 9.67% and 12.9%). The mainstream turbulence effect is diminished in the leading edge for higher blowing ratios (B = 0.8 and 1.2) but still exists on the flat sidewall region. Also, the leading edge heat transfer coefficient for blowing ratio of 0.8 increases with increasing mainstream turbulence; but the effect for other blowing ratios (B = 0.4 and 1.2) is not so systematic as for B = 0.8. Surface heat load is significantly reduced with leading edge film cooling.

Natural Convection Heat Transfer From a Horizontal Circular Cylinder With Constant Surface Heat Flux

2009 ◽  
Author(s):  
Maria Neagu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Circular Cylinder ◽  
Surface Heat Flux ◽  
Convection Heat Transfer ◽  
Surface Heat ◽  
Governing Equations ◽  
System Parameters ◽  
The Finite Difference Method ◽  
Horizontal Circular Cylinder

This work analyses the natural convective heat transfer from a horizontal circular cylinder with constant surface heat flux using radial equally spaced exterior low conductivity baffles. The dimensionless governing equations in the stream function–vorticity formulation were solved using the finite difference method. The influence of the system parameters, the number of baffles and the baffle height, on the average Nusselt number is presented.

Analytical Solution for Unsteady Heat Transfer in a Pipe

1988 ◽  
Vol 110 (4a) ◽  
pp. 850-854 ◽  
Author(s):  
J. Sucec
Keyword(s):  
Heat Transfer ◽  
Pipe Wall ◽  
Ambient Medium ◽  
Sudden Change ◽  
Thermal Capacity ◽  
Surface Heat ◽  
Unsteady Heat Transfer ◽  
Adequate Accuracy ◽  
Steady Solutions ◽  
Temperature Surface

Under consideration is transient, convective heat transfer to a fluid flow within a pipe due to a sudden change in the temperature of the ambient medium outside the pipe. A solution is developed by the Laplace transformation, for the fastest portion of the transient, which gives the pipe wall temperature, surface heat flux, and fluid bulk mean temperature. These analytical results are compared with available finite difference results and with quasi-steady solutions. A criterion is developed that indicates when the zero thermal capacity wall solution can be used with adequate accuracy.

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