Influence of the Entropy Layer on Turbulence Transition of the Supersonic Boundary Layer in the Wake with Isolated Rough
- PDF / 864,903 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 98 Downloads / 175 Views
uence of the Entropy Layer on Turbulence Transition of the Supersonic Boundary Layer in the Wake with Isolated Roughnesses I. O. Pogorelova,b,* and P. V. Chuvakhova, b, ** a
Zhukovsky Central Aerohydrodynamic Institute (TsAGI), Zhukovsky, Moscow region, Russia Moscow Physico-Technical Institute (State University), Dolgoprudnyi, Moscow region, Russia *e-mail: [email protected] **e-mail: [email protected]
b
Received March 1, 2020; revised March 12, 2020; accepted March 12, 2020
Abstract—The influence of the entropy layer generated by a small bluntness of the flat plate leading edge on laminar-turbulent supersonic boundary layer transition in the wake behind isolated roughness elements located on the plate surface is studied when the bluntness radius is varied. The experiments are carried out at the Mach number M = 6 over the Reynolds number range (0.4–2.3) × 106. The Reynolds number is calculated on the basis of the free-stream parameters at the point of roughness. The well-known correlation dependences are verified and the transition criterion is estimated. Keywords: supersonic boundary layer, laminar-turbulent transition, isolated roughness, experiment, correlation, criterion, reversal DOI: 10.1134/S0015462820050110
In designing a supersonic vehicle, it is necessary to take into account the location of laminar-turbulent transition in the boundary layer. Transition leads to increase in the friction resistance and the heat flux to the surface. This determines the requirements to the heat protection of vehicle elements. Under the lownoise flight conditions, turbulence transition can be adequately described for flow past fairly smooth surfaces within the framework of the linear stability theory. In practice, the surface smoothness is not ideal and early laminar-turbulent transition can be initiated by a fairly large surface roughness. The roughness generates a vortex wake and can lead to the so-called “by-pass” laminar-turbulent transition in which there is no linear stage of the development of perturbations [1]. The roughnesses whose height is lower than a certain critical value have no significant effect on the transition location (subcritical regime). As the height increases, the wake downstream of the roughness disintegrates into a turbulent wedge (supercritical regime). The wedge vertex is rapidly displaced upstream until the roughness reaches the effective height. Thereafter, the wedge vertex location reacts only slightly on growth in the roughness and remains at a certain, almost constant, distance downstream of the roughness [2]. Obviously, there exist no theory and universal criteria which could satisfactorily predict the location of laminar-turbulent transition in the wake behind an isolated roughness. The leading edges of vehicles are made blunted to decrease the heat loads. Gas crosses the strong (almost normal) shock wave in the neighborhood of bluntness, warms up, and expands above the plate surface by forming the entropy layer, i.e., the layer of hot low-density gas. The unabsorbed entr
Data Loading...
