On The Scaling And Unsteadiness Of Shock Induced Separation
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On the Scaling and Unsteadiness of Shock Induced Separation
Shock wave boundary layer interactions (SWBLI) are a common phenomenon in transonic and supersonic flows. The presence of shock waves, induced by specific geometrical configurations, cause a rapid increase of the pressure, wich can lead to flow separation. Examples of such interaction are found in amongts other rocket engine nozzles, on re-entry vehicles, in supersonic and hypersonic engine intakes, and at the tips of compressor and turbine blades. The interactions are important factors in vehicle development. Both the separated flow and the induced shock have been shows to be highly unsteady, causing pressure fluctuations and thermal loading. This generally leads to a degraded performance and possibly structural failure. The current work therefore aims to improve the physical understanding of the mechanisms that govern the interaction, with a special attention for the flow organisation and for the sources of the unsteadiness of the induced shock. Additioinally, it is verified wether the interaction can be controlled by means of upstream fluid injection. PIV measurements were performed, comparing several interactions for a range of shock intensities for a number of Mach and Reynolds numbers. It is proposed that relative importance of the different unsteadiness mechanisms (upstream, downstream) shifts with the imposed shock intensity. The onset of separation is Reynolds number independent for turbulent boundary layers. The interaction length is however governed by the both the Reynolds number and the Mach number.
Measurements of a Three-dimensional Shock-boundary Layer Interaction
Author: David Benjamin Helmer
language: en
Publisher: Stanford University
Release Date: 2011
A series of measurements were taken of the shock-boundary layer interaction (SBLI) in a Mach 2.1 continuously operated wind tunnel. The SBLI was generated by a small (~1.1mm tall) 20° wedge located on the top wall, and data were taken both in the region near the compression wedge and in the area where this shock impinged on the bottom wall. PIV was the primary measurement tool in both locations, though pressure data were also acquired near the compression wedge. Data were acquired at 4 spanwise locations to study the three-dimensionality of the flow. Both interactions were found to be highly 3-D, with a stronger interaction observed near the channel centerline. Evidence of a corner vortical structure in the compression corner was observed, and substantiated by CFD. Intermittent flow reversal was seen in the reflected shock interaction near the channel centerline, though not in the corners. The data suggest the presence of vortical structures generated near the channel centerline and pushed towards the sidewalls. Following the characterization of the base case, a Monte Carlo experiment was performed in which geometric perturbations were installed along the bottom wall of the wind tunnel and their effect on the flow was studied. The Monte Carlo device was designed and installed at the location predicted to be most sensitive by CFD. The majority of the locations initially tested displayed minimal sensitivity, with only the largest and most upstream quasi-2D cases showing significant effects on the flow at the corner. The perturbation device was redesigned and moved upstream, and additional quasi-2D cases were tested. It was found that some configurations accelerated the flow and strengthened the primary shock, while others slowed the flow and weakened the shock. Overall, the flow was observed to be very sensitive to some perturbations, but only to those located within a limited range of streamwise positions, and with a wide variety of system responses possible.
Unsteady Effects of Shock Wave induced Separation
Author: Piotr Doerffer
language: en
Publisher: Springer Science & Business Media
Release Date: 2010-11-25
This volume contains description of experimental and numerical results obtained in the UFAST project. The goal of the project was to generate experiment data bank providing unsteady characteristics of the shock boundary layer interaction. The experiments concerned basic-reference cases and the cases with application of flow control devices. Obtained new data bank have been used for the comparison with available simulation techniques, starting from RANS, through URANS, LES and hybrid RANS-LES methods. New understanding of flow physics as well as ability of different numerical methods in the prediction of such unsteady flow phenomena will be discussed.