The Existence of Three-dimensional Perturbations in the Reattachment of a Two-dimensional Supersonic Boundary Layer After Separation

The Existence of Three-dimensional Perturbations in the Reattachment of a Two-dimensional Supersonic Boundary Layer After Separation
Author: Jean J. Ginoux
Publisher:
Total Pages: 18
Release: 1960
Genre: Aerodynamics, Supersonic
ISBN:

The reattachment region of a laminar boundary layer after separation has been investigated at a Mach number of 2.16. Two-dimensional compression corners and backward or forward facing step models were used. The case of interaction between a shock wave and a laminar boundary layer was also considered. Surface flow was observed by a sublimation technique and detailed span-wise surveys were made in the reattachment region of the flow with total-head probes. Strong, regular and repeatable span-wise perturbations were observed in the boundary layer; these could not be explained by irregularities either in the air flow upstream of the models or in the models themselves. It was found in all cases that street-like flow perturbations existedup to the point where transition occurred. A systematic investigation was made on backward facing steps in order to find out the effects of step height and boundary-layer thickness on the wave length of the flow perturbations. (Author).

SUPERSONIC FLOW SEPARATION ON A BACKWARD FACING STEP.

SUPERSONIC FLOW SEPARATION ON A BACKWARD FACING STEP.
Author:
Publisher:
Total Pages: 42
Release: 1966
Genre:
ISBN:

The paper describes an experimental survey of flow separation on backward facing steps having different heights at a Mach number of 2.4. Reattachment and critical points are found for three regimes, laminar, transitional, and turbulent. Reattachment occurs at a point where the pressure is 35% of the free stream value for turbulent flow, and 60% of this value in the laminar case. The length of the free shear layer is found to be one-half that of the separating streamline, a result which emphasizes the importance of the reattachment region. The flow downstream of the critical point is found to be relatively independent of the base flow. Disturbances in the spanwise direction are always observed in laminar flow but do not affect the base pressure.

Base Pressure Behind Two-dimensional and Axially Symmetric Backward Facing Steps in a Turbulent Supersonic Flow

Base Pressure Behind Two-dimensional and Axially Symmetric Backward Facing Steps in a Turbulent Supersonic Flow
Author: Josef Rom
Publisher:
Total Pages: 30
Release: 1963
Genre:
ISBN:

The pressure behind a two-dimensional step in supersonic turbulent flow is calculated by the use of the Crocco-Lees momentum integral method. However, instead of assuming a constant mixing rate of k=0.03, it is assumed that C, the average value of turbulent mixing rate correlation function between separation and shock impingement positions, is constant. This assumption considers the turbulent mixing to be similar, in general, to the laminar case except for the much higher mixing rate. The assumption of C, as constant leads to a similarity parameter for the pressure behing a two-dimensional step equal to Re sub L to the minus 3/5 power times h/l. Pressure distribution behind two-dimensional steps is measured at Mach number of 2.25 and Reynolds numbers between 0.35 to 5x Re sub L to the minus 3/5 power times h/l. Good agreement is found between the analytical calculations and the experimental data as well as other published experimental data. Pressure distribution behind axially-symmetric backward facing steps is measured at Mach number 2.25 and Reynolds numbers of 3 to 10 to the 6th power. It is shown that the flow around the axially-symmetric step is similar to that about a free base and is the correlated using the parameter Re sub L to the minus 1/5 power times h/l. Comparison is presented also with published data and good agreement is found. (Author).

Preliminary Report on a Study of Separated Flows in Supersonic and Subsonic Streams

Preliminary Report on a Study of Separated Flows in Supersonic and Subsonic Streams
Author: Dean R. Chapman
Publisher:
Total Pages: 24
Release: 1956
Genre: Aerodynamics
ISBN:

Some results are described of fundamental research conducted on various flow separation phenomena in two-dimensional streams. Experimental and theoretical results are described for the pressure rise across a reattachment region, and for the Reynolds number dependence of the pressure rise to a separation point. Observations are made throughout of the location of transition relative to reattachment and to separation, since this relative location turned out to be the dominant variable investigated.

LAMINAR SEPARATION IN SUPERSONIC FLOW.

LAMINAR SEPARATION IN SUPERSONIC FLOW.
Author: Jean J. Ginoux
Publisher:
Total Pages: 1
Release: 1962
Genre:
ISBN:

A study of three-dimensional flow perturbations in laminar supersonic flows was made on flat plates with sweptback leading edges and in the reattachment region of the flow over flat plates with backward-facing steps. It was shown that a cross-flow existed in the boundary layer on flat plates with supersonic sweptback leading edges of small bluntness, which increased in magnitude from the centerline towards the sides of the models. In separated flows, only an extremely small amount of cross-flow was needed to destabilize the flow and to create regular spanwise variations in total pressure. Larger cross-flows, controlled by a systematic variation of the angle of sweep either of the leading edge or of the edge of the step, had no further effect. Detailed surveys made in a reattaching laminar supersonic flow with a static probe showed that the three-dimensional perturbations that existed in the boundary layer were formed by two layers of equidistant contra-rotating streamwise vortices: one located near the wall and a second one near the outer edge of the boundary layer. (Author).