Home – Home – Jornals – Thermophysics and Aeromechanics 2012 number 5

The mechanism of production of nonstationary Görtler vortices in a boundary layer on concave wall by surface nonuniformities (vibrations and roughness) has been experimentally examined. The nonuniformities were produced by a specially developed disturbance source. They were controlled, localized along the streamwise coordinate, and periodic over the span of the experi-mental model. Tests in a low-turbulence wind tunnel have proved that the disturbance source is an efficient means of experimental study of the re-ceptivity and stability problem for boundary layers dominated by Görtler instability. The operation of the dis-turbance source leads to the production of small-amplitude nonstationary Görtler vortices (tenth or hundredth fractions of a per cent of the free-stream velocity) with predefined characteristics (frequency and spanwise wavelength). In our experiments, we quantitatively examined the problem of linear receptivity of boundary layer to surface nonuniformities in a broad range of frequencies for the most dangerous spanwise scales of Görtler vortices. The values of the amplitudes and phases of the receptivity coefficients were determined. The amplitudes proved to be much smaller in magnitude in comparison with the excitation of modes of hydrodynamic instabilities of other types (Tollmien—Schlichting waves and cross-flow-instability modes). It was found that, with increasing the frequency, the amplitudes of the receptivity coefficients showed a distinct growth while for high frequencies those amplitudes also exhibited a growth with the spanwise scale of perturbations, although for stationary surface roughness no effect due to this scale was observed. It was found that the dependences on frequency of the efficiency of the mechanisms of stability and receptivity showed opposing behaviors, were in competition, and could partially compensate each other, promoting, thus, the production of boundary-layer Görtler vortices in a broad range of frequencies.

In the present study, we examined, both experimentally and theoretically, the influence of porous-coating thickness on the stability and laminar-turbulent transition of flat-plate supersonic boundary layer at free-stream Mach number M_∞ = 2. A qualitative agreement between the data calculated by the linear theory of stability and the experimental data on the transition obtained for models with different porous-coating thicknesses was established. We show that with decreasing (within a certain interval) the porous-coating thickness the boundary layer becomes more stable to perturbations, and the laminar-turbulent transition, more delayed.

This paper focuses on the design of a forward-facing cavity and opposing jet combined configuration for thermal protection system (TPS) of hypersonic vehicles. The cooling efficiency of the combined TPS was investigated numerically, and the numerical method was validated by the related experiment in the open literature. The flow field parameters, aerodynamic force, and surface heat flux distribution were obtained. The detailed numerical results show that this kind of combined TPS has an excellent impact on cooling the nose-tip, and it is suitable for the thermal protection of hypersonic vehicles which require long-range and time to cruise

The article describes the model of transcillatory heat transfer induced by gas bubbles buoyant in liquid. The temperature problem is reduced to the equivalent integral equation, and the velocity field in liquid phase is presented as structures of running and stationary waves. The relations for computing the coefficient of transcillatory transfer have been found.

The article provides results of experimental investigation of a fresh water motion in a flume with limited dimensions at lateral heating. The initial water temperature in the flume ranged from 0 to 22 ºС. It is shown that there are qualitative changes of the motion picture in the vicinity of initial temperature in the flume equal to the one at which water has maximal density (approximately 4 ºС). At an initial temperature in the flume exceeding or equal to 4 ºС, the heated water propagates in the form of a relatively thin surface jet, and at jet reflection from the flume end walls the heated water is accumulated only in the upper layer. When the initial temperature in the flume is below 4 ºС the convective instability develops. A part of the heated water sinks to the bottom. The paper provides respective illustrations and quantitative data on the distribution of temperature and velocity.