Unsteady laminar boundary layers in a compressible stagnation flow

1975 ◽  
Vol 70 (3) ◽  
pp. 561-572 ◽  
Author(s):  
C. S. Vimala ◽  
G. Nath
Keyword(s):  
Free Stream ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Compressible Boundary Layer ◽  
Two Dimensional ◽  
Stagnation Flow ◽  
Laminar Boundary Layers ◽  
Implicit Finite Difference ◽  
Layer Flow ◽  
Heat Transfer Parameter

The unsteady laminar compressible boundary-layer flow in the immediate vicinity of a two-dimensional stagnation point due to an incident stream whose velocity varies arbitrarily with time is considered. The governing partial differential equations, involving both time and the independent similarity variable, are transformed into new co-ordinates with finite ranges by means of a transformation which maps an infinite interval into a finite one. The resulting equations are solved by converting them into a matrix equation through the application of implicit finite-difference formulae. Computations have been carried out for two particular unsteady free-stream velocity distributions: (i) a constantly accelerating stream and (ii) a fluctuating stream. The results show that in the former case both the skin-friction and the heat-transfer parameter increase steadily with time after a certain instant, while in the latter they oscillate, thus responding to the fluctuations in the free-stream velocity.

Skin Friction and Heat Transfer for Laminar Boundary-Layer Flow With Variable Properties and Variable Free-Stream Velocity

1953 ◽  
Vol 20 (3) ◽  
pp. 415-421
Author(s):  
S. Levy ◽  
R. A. Seban
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Prandtl Number ◽  
Skin Friction ◽  
Laminar Boundary Layer ◽  
Boundary Layer Flow ◽  
Free Stream ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Layer Flow

Abstract Numerical solutions of the momentum and energy equations are presented for particular types of laminar boundary-layer flow analogous to the Hartree “wedge flows.” Variation of the viscosity and of the thermal conductivity is considered under the circumstances of no dissipation, favorable pressure gradient, and the product of conductivity and density a constant. The solution is based on approximate representations of the velocity and temperature profiles in the boundary layer and these are of such character that the labor of calculation is minimized and the accuracy of the results preserved. The differential equations are reduced to two algebraic equations which rapidly yield the skin friction and the heat transfer in terms of the wall to free-stream temperature ratio for the desired value of Prandtl number. Numerical results are given for a range of wedge flows with gases of Prandtl number 0.70 and 1.0. These results reveal that when the free-stream velocity is variable the temperature difference between the wall and the free stream exerts a substantial effect on the velocity distribution in the boundary layer and on the skin-friction coefficient. Alternatively, the heat-transfer coefficient is not affected radically. A calculation method is presented for the determination of the heat transfer and skin friction for a flow with an arbitrary variation of velocity over an isothermal surface. This method utilizes the results of the present analysis for the variable property wedge flows.

Three-dimensional laminar boundary layers in crosswise pressure gradients

1974 ◽  
Vol 66 (4) ◽  
pp. 641-655 ◽  
Author(s):  
J. H. Horlock ◽  
A. K. Lewkowicz ◽  
J. Wordsworth
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Free Stream ◽  
Three Dimensional ◽  
Cross Flow ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Laminar Boundary Layers ◽  
The Cross

Two attempts were made to develop a three-dimensional laminar boundary layer in the flow over a flat plate in a curved duct, establishing a negligible streamwise pressure gradient and, at the same time, an appreciable crosswise pressure gradient.A first series of measurements was undertaken keeping the free-stream velocity at about 30 ft/s; the boundary layer was expected to be laminar, but appears to have been transitional. As was to be expected, the cross-flow in the boundary layer decreased gradually as the flow became progressively more turbulent.In a second experiment, at a lower free-stream velocity of approximately 10 ft/s, the boundary layer was laminar. Its streamwise profile resembled closely the Blasius form, but the cross-flow near the edge of the boundary layer appears to have exceeded that predicted theoretically. However, there was a substantial experimental scatter in the measurements of the yaw angle, which in laminar boundary layers is difficult to obtain accurately.

The Effect of Slot Height and Slot-Turbulence Intensity on the Effectiveness of the Uniform Density, Two-Dimensional Wall Jet

1968 ◽  
Vol 90 (4) ◽  
pp. 469-475 ◽  
Author(s):  
S. C. Kacker ◽  
J. H. Whitelaw
Keyword(s):  
Turbulence Intensity ◽  
Free Stream ◽  
Velocity Ratio ◽  
Free Stream Velocity ◽  
Stream Velocity ◽  
Uniform Density ◽  
Wall Jet ◽  
Two Dimensional ◽  
Significant Parameter

This paper presents measurements of the impervious-wall effectiveness of a two-dimensional wall jet obtained using a constant value of lip thickness, 0.032 in. and four slot heights, viz., 0.5, 0.25, 0.132, and 0.074 in. The measurements are in the range of slot-to-free-stream velocity ratio 0.288⩽u¯C/uG⩽2.66 and clearly demonstrate that, in the region where the velocity ratio is close to unity, the effectiveness is greatly dependent upon the slot height. The reason for this dependence is investigated and additional measurements are presented to show that the influence of the slot turbulence intensity on the effectiveness is small. It is concluded that the ratio of slot lip thickness to slot height is the most significant parameter and that the effect of an increase in this ratio is to decrease the effectiveness.

Sign in / Sign up

Export Citation Format

Share Document