Suppressing a Laminar Flow Separation Zone by Spark Discharge at Mach Number M = 1.43

The influence of flow perturbations generated by an electric discharge on the region of interaction between a shock wave and laminar boundary layer in the flow on a flat plate at a Mach number of M = 1.43 has been experimentally studied. The oblique shock wave generated by a wedge mounted above the plate induced separation of the flow, while perturbations in the flow were introduced by a spark discharge on the model plate surface. It is established that the discharge leads to the formation of turbulent and thermal spots. The turbulent spot suppresses the separation zone, while the thermal spot leads to a local increase in the boundary layer thickness in the interaction zone.

     

Supersonic Flow of Viscous Gas in a Flat Channel at High Values of the Reynolds Number

Based on numerical analysis of two-dimensional Reynolds equations using the differential model of turbulence, the structure of flow field and aerodynamic characteristics of a flat channel with variable cross section at the inlet Mach number of four is investigated in the range of Reynolds numbers Re = 10⁵–10⁷. According to the calculation results, the interaction between a shock and a laminar boundary layer results in the emergence of a closed separation zone. During interaction with a turbulent boundary layer, two flow schemes are possible, depending on the intensity of incident shock, namely, without and with separation. The extrapolation of calculation data to nonviscous flow (limiting transition Re ) shows that the classical scheme of regular reflection of the shock from a flat surface corresponds to interaction without separation. Corresponding to interaction with separation is the flow scheme with formation of a small closed separation zone in which a subsonic circulation flow takes place.     

An experimental investigation of the Reynolds number effect on a normal shock wave-turbulent boundary layer interaction on a curved wall

Summary The presented experiment concerned an interaction between a normal shock wave, terminating a local supersonic area in a curved duct, and a turbulent boundary layer developed along the convex wall. This paper deals with the Reynolds number effect upon the interaction structure.The measurements included flow parameters distribution determination, boundary layer development through the interaction area and the shock wave topography visualization. In order to gain more information about separation the wall oil tracing has been applied. The comparison of our results with other published data is presented.With 11 FiguresThe experiments have been carried out at the Institut für Strömungslehre und Strömungsmaschinen, Karlsruhe Universität, Karlsruhe, Federal Republic of Germany.     

What makes the difference between shock boundary-layer interaction on an airfoil and on a swept wing?

Summary Swept wing flows are characterized by the curvature of the streamlines in the projection to the wing plan and by the skewing of the velocity profile in the boundary layer. The aerodynamic performance of supercritical wings at transonic speeds is trongly influenced by the interaction between a weak shock front and a turbulent boundary layer. The characteristic elements of this interaction are the precompression, the post-shock expansion, and the shock diffusion. The differences between the interactive flow over an airfoil and over a swept wing are elaborated by the comparison between the two-dimensional case and the flow with superposed tangential velocity.     

Interaction of a shock wave with a turbulent boundary layer on a heated surface

The interaction of a shock wave with a turbulent boundary layer has been studied. A stream has been diagnosed using non-invasive visualization (schlieren method). During the investigation the effect of surface heating on the length of boundary layer separation has been studied. It has been discovered that during surface heating the dependence of the length of separation on the temperature ratio is approximated using a linear law.     

An experimental investigation of the Mach number effect upon a normal shock wave — Tubulent boundary layer interaction on a curved wall

Summary The Mach number effect upon the normal shock wave — turbulent boundary interaction is investigated experimentally.The measurements included flow parameters distribution determination, boundary layer development through the interaction area and the shock wave topography visualization. In order to have better insight into separation development the oil flow technique has been applied. The comparison of our results with other published data is presented.With 10 FiguresThe experiments have been carried out at the Institut für Strömungslehre und Strömungsmaschinen, Universität Karlsruhe, Federal Republic of Germany     

Interaction between a weak oblique shock wave and a turbulent boundary layer in purely supersonic flow

Summary The paper deals with the interaction of a weak oblique shock and a turbulent boundary layer at a flat plate at purely supersonic speeds. Except for a small region where nonlinear transonic effects are of importance analytical expressions for the pressure- and skin friction distributions are derived.With 6 Figures     

Laminar-turbulent transition in a supersonic boundary layer during initiation of a pulsed surface discharge

The near-surface layer structure in a supersonic airflow (M = 1.5) behind the plane shock wave has been experimentally studied in a shock tube. The flow structure was visualized using nanosecond pulsed distributed surface discharge. Different structures of plasma glow have been observed for the laminar and turbulent flow regimes in the boundary layer. The position of a region of the laminar-turbulent transition for different flow densities (0.11 and 0.19 kg/m³) has been determined and the critical Reynolds number (Re _k ～ 2.4 × 10⁵) for this transition has been evaluated.     

The interaction of shock waves with a boundary layer on a sharp plate and a blunted plate

The interaction of shock waves with a turbulent boundary layer on a sharp plate and a blunted plate is numerically investigated. The shock waves in the flow are generated by wedges installed on the flat plate. The flow is simulated by the dynamic equations of a viscous perfect gas. The effect of the blunting radius of the plate’s leading edge and the wedge angle on the flow field and the local aerodynamic coefficients is shown. The calculated results are in agreement with the experimental data.     

A local solution method for shock boundary-layer interaction on a swept wing

Summary The paper describes a local solution method for the calculation of the interaction between a weak shock front and a turbulent boundary layer on a swept wing. A multiple-deck approach allows the simplification of the governing equations according to the physical character of each deck. The mathematical model is based upon small-perturbation theory. The final boundary-layer solution is given by an iterative coupling of the solutions for each domain. The results are compared with experiments and with other theoretical solutions.     

Turbulent mixing development in a thin liquid layer accelerated by compressed air in a closed volume

It is demonstrated that a zone of turbulent mixing (TM) is developed at the unstable boundary of a thin liquid film accelerated by a hot compressed gas flow. When the TM zone reaches the opposite boundary, the film breaks into fragments and expands. As a result, the liquid film transforms into a layer comprising a dispersed liquid-gas mixture. The layer thickness increases with time and may be several dozens of times that of the initial liquid film.     

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.     

Turbulence in a Roughness Layer

Consideration is given to a model of turbulent flow in a roughness layer; the model is formed by the equations for turbulent momentum and turbulence-energy density and by free boundary conditions at self-establishing boundaries of the turbulent zone in the entire layer and in roughness cells. The model describes the interactions of the flow with the elements of roughness and the processes in the cells of different scales. Certain calculated characteristics of turbulence in vegetation are given. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 4, pp. 143–151, July–August, 2005.     

Experimental study on the particle accumulation phenomenon in seeded flows around a near-bottom-wall horizontal cylinder

In experiments of flows around a cylinder in a water channel, an interesting phenomenon is that a particle accumulation line obviously forms on the bottom of the channel. The present paper focuses on this phenomenon, and the formation mechanism of the particle accumulation line is in detail investigated experimentally with particle image velocimetry (PIV). The circular cylinder was set in a fully developed turbulent boundary layer with 12 gap ratios S/D ranging from 0 to 1.5 under two Reynolds numbers (1371 and 902) based on the momentum loss thickness. The possible mechanism of this phenomenon has been demonstrated with the experimental results: the separation takes place due to the interaction between the wake of the cylinder and the boundary layer of the plane wall, the gap flow separates from the wall downstream of the cylinder and causes an attachment vortex of low velocity area at about 1 to 2 cylinder diameters from the cylinder, where the particle accumulation line forms steadily.     

On the asymptotic layering of turbulent flows

The asymptotic structure of a turbulent boundary layer on a plate with a boundary-layer distributed suction, consisting of a suction zone, a viscous zone, a buffer zone, a velocity-defect zone, a Corrsin superlayer, and a irrotational-flow zone, has been determined. The analysis was carried out within the framework of the Reynolds equations with the use of the combined method of different scales and joined of asymptotic expansions. The Corrsin superlayer was interpreted as a discontinuity of turbulent stresses. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 2, pp. 322–329, March–April, 2008.     

Friction in the preseparation zone and heat transfer in the separation zone of a turbulent boundary layer in the flow of heated air in a diffuser with cooled walls

The friction in the preseparation zone and the heat transfer in the separation zone of turbulent boundary layer have been experimentally investigated for flows of heated air in diffusers with cooled walls. An experimental method of determining the separation point is proposed together with a criterial equation for calculating the heat transfer in the separation zone.     

Conjugate Turbulent Heat Transfer in the Zone of Incidence of a Pressure Shock on a Wall with a Porous Insert

The reduction of heat loads under conditions of transpiration cooling is analyzed using numerical simulation of convective heat transfer in the zone of pressure shock incidence on a solid surface subjected to a turbulent flow. The Darcy equation is used to preassign the boundary conditions in the Reynolds equations for the momentum components on a porous insert.     

Wavelet packet analysis of particle response to turbulent fluctuation

The fluid–particle synchronous measurements in a boundary layer wind tunnel were conducted to determine the particle concentration response to turbulent velocity fluctuation. Three groups of natural sand samples (diameter of 300–500, 100–125 and 63–80 μm) were employed in the experiments. Consecutive instants of saltating particles were recorded by using a high-speed digital camera at 2000 frames per second and a constant-temperature hot-wire anemometer was used to measure the turbulent fluctuation simultaneously. The particle concentration in the saltation layer was calculated by the dynamic-threshold binarization algorithm. The results confirm that the concentration fluctuation is a fairly typical stochastic process, and the low-frequency variation of particle concentration is closely related to the turbulent fluctuation. Moreover, a method was developed to apply wavelet packet transform to two-phase data analysis from the viewpoint of frequency-domain energy structure. Further analysis shows that the concentration fluctuation is predominant in the low frequency band less than 250 Hz. In addition, the particle concentration response to the turbulent fluctuation is significantly correlated with the particle diameter. For the fine particles (63–80 μm), medium particles (100–125 μm) and coarse particles (300–500 μm), the highest response frequencies of particle concentration variation to the turbulent fluctuation are 60, 40 and 30 Hz, respectively, which demonstrates that an appropriate sampling rate is crucial in saltation measurement. These qualitative and quantitative results are beneficial to understand the fluid–particle interaction mechanism.     

Grundlagenuntersuchung zu den Str?mungsverh?ltnissen in hochtourigen Turbinengleitlagern: Str?mung in einem Konfusor mit einseitig bewegter Berandung

The flow in a confusor with a plane moving wall was investigated both experimentally and numerically for a turbulent Reynolds-number of 9.95×10³. These fundamental results can be applied for journal bearings used in case of large turbo-machines. It is found that the moving wall (journal) leads to a turbulent boundary layer flow whereas the mean flow in the groove domains is turbulent with only weak secondary flow features like recirculation zones. By means of a comparison with LDA measurements it is shown that the Realizable k–ε-model is well suited for corresponding flow configurations.