Vortex boundary-layer interactions

The interaction of a turbulent boundary layer (on a flat plate) with a strong artificially-generated longitudinal vortex, which may or may not actually enter the boundary layer, was studied. Experiments, including extensive hot-wire measurements, were completed for the case in which the vortex does enter the boundary layer, and measurements for the somewhat simpler cases in which the boundary layer and vortex remain distinct are now in progress. Contours of total pressure (recently acquired) and of turbulent kinetic energy at various downstream positions are presented to show the overall development of the vortex imbedded in the boundary layer

Compressible turbulent boundary layer interaction experiments

Four phases of research results are reported: (1) experiments on the compressible turbulent boundary layer flow in a streamwise corner; (2) the two dimensional (2D) interaction of incident shock waves with a compressible turbulent boundary layer; (3) three dimensional (3D) shock/boundary layer interactions; and (4) cooperative experiments at Princeton and numerical computations at NASA-Ames

Numerical study of shock-wave/boundary layer interactions in premixed hydrogen-air hypersonic flows

A computational study of shock wave/boundary layer interactions involving premixed combustible gases, and the resulting combustion processes is presented. The analysis is carried out using a new fully implicit, total variation diminishing (TVD) code developed for solving the fully coupled Reynolds-averaged Navier-Stokes equations and species continuity equations in an efficient manner. To accelerate the convergence of the basic iterative procedure, this code is combined with vector extrapolation methods. The chemical nonequilibrium processes are simulated by means of a finite-rate chemistry model for hydrogen-air combustion. Several validation test cases are presented and the results compared with experimental data or with other computational results. The code is then applied to study shock wave/boundary layer interactions in a ram accelerator configuration. Results indicate a new combustion mechanism in which a shock wave induces combustion in the boundary layer, which then propagates outwards and downstream. At higher Mach numbers, spontaneous ignition in part of the boundary layer is observed, which eventually extends along the entire boundary layer at still higher values of the Mach number

Flow separation in shock wave boundary layer interactions at hypersonic speeds

An assessment is presented for the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consists mainly of two dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the subsequent changes in the flow empirical correlations for incipient separation are reviewed. The effects of the Mach number, Reynolds number, surface cooling and the methods of detecting separation are discussed. The pertinent experimental data for the separated flow characteristics in separated turbulent boundary layer shock interaction are also presented and discussed

The ISSI international study team on the martian PBL – status report and plan

Dynamical processes in the Martian boundary layer provide the means of communication between surface ice deposits and the free atmosphere, and the means of lifting dust from the surface. The boundary layer is therefore one of the most important components of the Martian climate system. The Martian boundary layer differs from that of the Earth in that it is more strongly forced, it is deeper, and the relative importance of radiative and convective heat fluxes in the lower boundary layer can be quite different. In order to understand the Martian boundary layer, a combination of theoretical, modeling and observational studies are necessary. Interactions between theorists, modelers, and observational scientists are needed to make progress and to provide a basis for analysis of data expected from Phoenix, Mars Science Laboratory, ExoMars and other future landed missions (such as a surface network mission), or missions such as balloons or other aircraft operating in the neutral atmosphere. The prime goal of this project under the auspices of the International Space Science Institute (ISSI) is to review and assess the current knowledge and understanding of Martian planetary boundary layer and its interactions with the surface and free atmosphere. We aim to promote international communication and collaboration to enhance the rate of acquisition of knowledge and understanding. This will be achieved through an International Study Team and publication of overview papers and individual reports on recent advances in this area

Viscous-Inviscid Interactions in a Boundary-Layer Flow Induced by a Vortex Array

In this paper we investigate the asymptotic validity of boundary layer theory. For a flow induced by a periodic row of point-vortices, we compare Prandtl's solution to Navier-Stokes solutions at different $Re$ numbers. We show how Prandtl's solution develops a finite time separation singularity. On the other hand Navier-Stokes solution is characterized by the presence of two kinds of viscous-inviscid interactions between the boundary layer and the outer flow. These interactions can be detected by the analysis of the enstrophy and of the pressure gradient on the wall. Moreover we apply the complex singularity tracking method to Prandtl and Navier-Stokes solutions and analyze the previous interactions from a different perspective

On Reflection of Shock Waves from Boundary Layers

Measurements of the reflection characteristics of shock waves from a flat surface with a laminar and turbulent boundary layer are presented. The investigations were carried out at Mach numbers from about 1.3 to 1.5 and a Reynolds number of 0.9 x 10^4. THe difference in the shock-wave interaction with laminar and turbulent boundary layers, first found in transonic flow is confirmed and ,investigated in detail for supersonic flow. The relative upstream influence of a shock wave impinging on a given boundary layer has been measured for both laminar and turbulent layers. The upstream influence of a shock wave in the laminar layer is found to be of the order of 50 bounday-layer thicknesses as compared with about 5 in the turbulent case. Separation almost always occurs in the laminar boundary layer. The separation is restricted to a region of finite extent upstream of the the shock wave. In the turbulent case no separation was found. A model of the flow near the point of impingement of the shock wave on the boundary layer is given for both cases. The difference between impulse-type and step-type shock waves is discussed and their interactions with the boundary layer are compared. Some general considerations on the experimental production of shock waves from wedges and cones are presented, as well as a discussion of boundary layer in supersonic flow. A few exampies of reflection of shock waves from supersonic shear layers are also presented

Calculation of turbulent shear stress in supersonic boundary layer flows

Turbulent shear stress distributions for supersonic boundary layer flows have been computed from experimental mean boundary layer data. The computations have been made by numerically integrating the time averaged continuity and streamwise momentum equations. Distributions have been obtained for flows upstream and downstream of shock-wave-boundary layer interactions and for both two-dimensional and axisymmetric flows. The computed results are compared with recently reported shear stress measurements which were obtained by hot wire anemometer and laser velocimeter techniques

Vortex/boundary-layer interactions: Data report, volume 1

This report summarizes the work done under NASA Grant NAGw-581, Vortex/Boundary Layer Interactions. The experimental methods are discussed in detail and numerical results are presented, but are not fully interpreted. This report should be useful to anyone who wishes to make further use of the data (available on floppy disc or magnetic tape) for the development of turbulence models or the validation of predictive methods. Journal papers are in course of preparation