Heat Transfer Effects of a Longitudinal Vortex Embedded in a Turbulent Boundary Layer

1987 ◽  
Vol 109 (1) ◽  
pp. 16-24 ◽  
Author(s):  
P. A. Eibeck ◽  
J. K. Eaton
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Delta Wing ◽  
Stanton Number ◽  
Longitudinal Vortex ◽  
Test Facility ◽  
Pressure Probe ◽  
Transfer Effects ◽  
Heat Transfer Effects

The heat transfer effects of an isolated longitudinal vortex embedded in a turbulent boundary layer were examined experimentally for vortex circulations ranging from Γ/U∞δ99 = 0.12 to 0.86. The test facility consisted of a two-dimensional boundary-layer wind tunnel, with a vortex introduced into the flow by a half-delta wing protruding from the surface. In all cases, the vortex size was of the same order as the boundary-layer thickness. Heat transfer measurements were made using a constant-heat-flux surface with 160 embedded thermocouples to provide high resolution of the surface-temperature distribution. Three-component mean-velocity measurements were made using a four-hole pressure probe. Spanwise profiles of the Stanton number showed local increases as large as 24 percent and decreases of approximately 14 percent. The perturbation to the Stanton number was persistent to the end of the test section, a length of over 100 initial boundary-layer thicknesses. The weakest vortices examined showed smaller heat transfer effects, but the Stanton number profiles were nearly identical for the three cases with circulation greater than Γ/U∞δ99 = 0.53 cm. The local increase in the Stanton number is attributed to a thinning of the boundary layer on the downwash side of the vortex.

The Effect of Embedded Longitudinal Vortex Arrays on Turbulent Boundary Layer Heat Transfer

1994 ◽  
Vol 116 (4) ◽  
pp. 871-879 ◽  
Author(s):  
W. R. Pauley ◽  
J. K. Eaton
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Secondary Flow ◽  
Layer Structure ◽  
Longitudinal Vortex ◽  
Vortex Pairs ◽  
Dimensional Boundary ◽  
Minimal Modification ◽  
Vortex Patterns

Heat transfer and fluid mechanics data were obtained for a turbulent boundary layer with arrays of embedded streamwise vortices containing both counterrotating and corotating vortex pairs. The data show that these arrays can cause both large local variations in the heat transfer rate and significant net heat transfer augmentation over large areas. Close proximity of other vortices strongly affects the development of the vortex arrays by modifying the trajectory that they follow. The vortices in turn produce strong distortion of the normal two-dimensional boundary layer structure, which is due to their secondary flow. When one vortex convects another toward the wall, a strong boundary layer distortion occurs. The heat transfer is elevated where the secondary flow is directed toward the wall and reduced where the secondary flow is directed away from the wall. When adjacent vortices lift their neighbor away from the wall, minimal modification of the heat transfer results. The primary influence of grouping multiple vortex pairs into arrays is the development of stable patterns of vortices. These stable vortex patterns produce vortices that interact with the boundary layer and strongly modify the heat transfer far downstream, even where the vortices have decayed in strength.

scholarly journals The Turbulent Boundary Layer on a Porous Plate: Experimental Heat Transfer with Uniform Blowing and Suction, with Moderately Strong Acceleration

1972 ◽  
Vol 94 (1) ◽  
pp. 111-118 ◽  
Author(s):  
W. H. Thielbahr ◽  
W. M. Kays ◽  
R. J. Moffat
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Porous Plate ◽  
Stanton Number ◽  
Graphical Form ◽  
Temperature Dependent ◽  
Experimental Heat ◽  
Experimental Heat Transfer ◽  
Fluid Properties

Experimental data are presented for heat transfer to the turbulent boundary layer subjected to transpiration and acceleration at constant values of the acceleration parameter K = (ν/U∞2)(dU∞/dx) of approximately 1.45 × 10−6. This is a moderately strong acceleration, but not so strong as to result in laminarization of the boundary layer. The results for transpiration fractions F of −0.002, 0.0, and +0.0058 are presented in detail in tabular form, and in graphs of Stanton number versus enthalpy thickness Reynolds number. In addition, temperature profiles at several stations are presented. Stanton number results for F = −0.004, +0.002, and +0.004 are also presented, but in graphical form only. The data were obtained using air as both the free-stream and the transpired fluid, at relatively low velocities, and with temperature differences sufficiently low (approximately 40 deg F) that the influence of temperature-dependent fluid properties is minimal. All data were obtained with the surface maintained at a temperature invariant in the direction of flow.

Experimental Heat Transfer Behavior of a Turbulent Boundary Layer on a Rough Surface With Blowing

1978 ◽  
Vol 100 (1) ◽  
pp. 134-142 ◽  
Author(s):  
R. J. Moffat ◽  
J. M. Healzer ◽  
W. M. Kays
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Rough Surface ◽  
Stanton Number ◽  
Stream Velocity ◽  
Experimental Heat ◽  
Spherical Elements ◽  
Blowing Parameter

Heat transfer measurements were made with a turbulent boundary layer on a rough, permeable plate with and without blowing. The plate was an idealization of sand-grain roughness, comprised of 1.25 mm spherical elements arranged in a most-dense array with their crests coplanar. Five velocities were tested, between 9.6 and 73 m/s, and five values of the blowing fraction, vo/u∞, up to 0.008. These conditions were expected to produce values of the roughness Reynolds number (Reτ = uτks/ν) in the “transitional” and “fully rough” regimes (5 ≤ Reτ, ≤ 70, Reτ > 70). With no blowing, the measured Stanton numbers were substantially independent of velocity everywhere downstream of transition. The data lay within ±7 percent of the mean for all velocities even though the roughness Reynolds number became as low as 14. It is not possible to determine from the heal transfer data alone whether the boundary layer was in the fully rough state down to Re = 14, or whether the Stanton number in the transitionally rough state is simply less than 7 percent different from the fully rough value for this roughness geometry. The following empirical equations describe the data from the present experiments for no blowing: Cf2=0.0036θr−0.25St=0.0034Δr−0.25 In these equations, r is the radius of the spherical elements comprising the surface, θ is the momentum thickness, and Δ is the enthalpy thickness of the boundary layer. Blowing through the rough surface reduced the Stanton number and also the roughness Reynolds number. The Stanton number appears to have remained independent of free stream velocity even at high blowing; but experimental uncertainty (estimated to be ±0.0001 Stanton number units) makes it difficult to be certain. Roughness Reynolds numbers as low as nine were achieved. A correlating equation previously found useful for smooth walls with blowing was found to be applicable, with interpretation, to the rough wall case as well: StSt0Δ=ln(1+B)B1.25(1+B).25 Here, St is the value of Stanton number with blowing at a particular value of Δ (the enthalpy thickness). St0 is the value of Stanton number without blowing at the same enthalpy thickness. The symbol B denotes the blowing parameter, vo/u∞ St. The comparison must be made at constant Δ for rough walls, while for smooth walls it must be made at constant ReΔ.

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