P. A. Polivanov

On the determination of the position of laminar-turbulent transition in boundary layer by optical methods

As a rule, aerodynamic studies at hypersonic flow velocities are carried out in short-duration wind-tunnel facilities. For such facilities, optical diagnostic methods are most preferable. In the present study, we give for the first time a comparison of two methods for determining the end of laminar-turbulent transition: from the distribution of heat fluxes and from schlieren visualization data for the boundary-layer flow. Parametric data on the position of the transition are obtained. These data can be used in the future as reference ones while calibrating semi-empirical calculation models for the transition.

Effect of the surface roughness of blunt cone forebody on the position of laminar-turbulent transition

In the present paper, data on the effect of the surface roughness of blunt cone forebody on the position of laminar-turbulent transition are reported. The study was carried out under freestream Mach 5.95. It was found that the roughness position plays a substantial role in the transition process. Critical Reynolds numbers at which the laminar-turbulent transition occurs on the nose-tip of the model were identified. For the first time, hysteresis in transition position was observed.

Correlations study in shock wave/turbulent boundary layer interaction

The shock waves/turbulent boundary layer interaction is a problem of critical importance that is frequently encountered in designing flying vehicles. Presently, the most topical issue is the investigation of nonstationary phenomena (in particular, low-frequency effects) involved in this interaction. We have experimentally studied separated flows in the zone of interaction between an obliquely incident shock wave and a turbulent boundary layer at a Mach number of M = 2. Correlation data in the separation zone and the upstream flow were obtained. It is established that low-frequency oscillations in the reflected shock are related to the pulsation in the inflow boundary layer.

An experimental study of the natural noise in the Transit-M hypersonic wind tunnel

Tests were performed at Mach number M = 6. Observations of flow pulsations were performed with the help of high-frequency measurements of pressure and heat fluxes and with the help of hot-wire anemometry. Measurements were carried out in a broad range of Re1 numbers at various orientations and locations of sensors with respect to the nozzle exit plane. It is shown that the Transit-M noise varies weakly over the longitudinal coordinate, whereas on moving along the radial coordinate, some increase of the fluctuation level is observed due to approaching the mixing layer. Also, the distribution of axial asymmetry of the noise level was obtained.

The influence of the laminar–turbulent transition on the interaction between the shock wave and boundary layer at a low supersonic Mach number

An experimental study is devoted to the problem of the interaction between the shock wave and boundary layer. The influence of the approaching boundary layer state on parameters of the interaction region is studied by use of measurements of velocity fields. It is shown that the case in which the interaction occurs near the zone of the laminar–turbulent transition in the boundary layer is optimum. The possibility of controlling for the interaction by means of turbulizers is studied.

Investigation of a nonstationary flow field generated by a dielectric barrier discharge

The search for ways of controlling a flow over flight vehicles is today an extremely topical issue, since the limiting capabilities of standard control methods are the bulk of the progress of space technology. A promising technique in this respect is the application of activators using a low-temperature plasma. Specifically, these electrogasdynamic devices can directly convert electrical energy to a mechanical action on the flow. An activator based on a dielectric barrier discharge is considered. The nonstationary behavior of the activator is studied by measuring the electrodynamic parameters of the discharge and also by measuring induced velocity fields with particle image velocimetry. The instantaneous and integral parameters of the gas acceleration stage are found, and the efficiency of the activator is determined.

Effects of temperature factor of cone nose-tip on a transition to turbulence

During the flight of a hypersonic vehicle the areas of local heating of the surface can appear due to various reasons: the local separation zone, the incident shock wave, the joints of different materials and so forth. These areas change the temperature factor, i.e. the ratio of the surface temperature to the recovery temperature. Previous studies have shown that a local change of the temperature factor strongly influences the position of the laminar-turbulent transition in hypersonic boundary layer [1]. It was also shown that the degree of this effect depends on the position of the local heating/cooling area of the model surface. The leading edge or nose-tip of the model is an important area where the processes of receptivity occur. Disturbances converted to inner pulsation of the boundary layer is gradually increasing downstream, provoking non-linear processes, resulting in a laminar-turbulent transition. It is well known that the bluntness of model-tip substantially shifts transition position downstrea...

The use of wavelet transform for the correlation analysis of boundary-layer pulsations

As a rule, experimental studies at hypersonic Mach numbers are carried out in short-duration wind tunnels. Under such conditions, data on boundary-layer pulsations are primarily measured by surface pressure sensors. There are many factors affecting the level of pulsations at model walls; that is why the cross-correlation analysis is often invoked to analyze the development of wave packets in boundary layer. However, the standard correlation analysis very often fails in providing the possibility to trace the evolution of wave packets. In the present publication, we propose a new method for obtaining cross-correlation data based on the wavelet transform.

Nonstationary phenomena in the region of shock-wave interaction with a boundary layer at transonic flow velocities

Nonstationary characteristics of detached flow have been experimentally studied during interaction of the boundary layer with a shock wave that appears on a profiled bump in transonic flow. The experiments were performed with variable shock-wave intensity and position in a T-325 wind tunnel. The flow was studied using methods of schlieren imaging, measuring average pressure and its pulsations on the surface of a model, and determining velocity fields by particle image velocimetry. Analysis of the experimental data showed that the observed shock-wave oscillations and flow pulsations in the detachment zone were related to disturbances present in the oncoming boundary layer.

Turbulization of the wake behind a single roughness element on a blunted body at a hypersonic Mach number

The influence of a cylinder-shaped single roughness element on the laminar–turbulent transition in the presence of an entropy layer is experimentally studied. The experiments are performed on a blunted cone model at the Mach number M = 5. The roughness element is located on the blunted tip of the model. Information about the mean and fluctuating parameters of the boundary layer in the wake behind the roughness element is obtained by using hot-wire anemometry. It is shown that flow turbulization behind the roughness elements occurs at the local Reynolds number calculated on the basis of the roughness element height and equal to 400–500. It is found that the presence of the roughness element exerts a significant effect on the unsteady characteristics of the boundary layer if the roughness element height is smaller than the effective value.