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Author: Louis Jacques Souverein
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
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.
Author: Louis Jacques Souverein
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
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.
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Category :
Languages : en
Pages : 55
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Book Description
The purpose of this work was to (I) examine separation shock wave unsteadiness in different turbulent interactions and determine whether a universal model describing the unsteadiness could be developed, and (II) determine whether or not the observed unsteadiness is a feature of turbulent flow in general, or is specific to the wind tunnel environment. To this end, wall and pitot pressure fluctuation measurements were made in interactions generated by unswept and 25 deg swept compression ramp models, and by 8 deg and 30 deg swept blunt-fin models in a high Reynolds number, Mach 5 turbulent boundary layer. It is clear that the high-frequency, jittery motion of the separation shock is the result of the passage through the wave of individual large-scale turbulent structures. Thus, this component of the unsteadiness is an inherent feature of all turbulent flows. The primary outstanding question concerns the cause of the low-frequency expansion/contraction of the separated flow which is characterized by the large-scale, long-duration excursions of the separation shock wave. Preliminary experimental work to address this question has revealed two very interesting, complementary results. First, there is a distinct correlation between large-scale expansion or contraction of the separated flow and long duration (i.e., low-frequency) falls or rises in pitot pressure in the incoming turbulent boundary layer. Second, results from the same experiment show that the ensemble-averaged pitot pressure at a fixed location in the incoming undisturbed boundary layer correlates with separation shock wave position.
Author: Piotr Doerffer
Publisher: Springer Science & Business Media
ISBN: 3642030041
Category : Technology & Engineering
Languages : en
Pages : 350
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Book Description
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.
Author: Holger Babinsky
Publisher: Cambridge University Press
ISBN: 1139498649
Category : Technology & Engineering
Languages : en
Pages : 481
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Book Description
Shock wave-boundary-layer interaction (SBLI) is a fundamental phenomenon in gas dynamics that is observed in many practical situations, ranging from transonic aircraft wings to hypersonic vehicles and engines. SBLIs have the potential to pose serious problems in a flowfield; hence they often prove to be a critical - or even design limiting - issue for many aerospace applications. This is the first book devoted solely to a comprehensive, state-of-the-art explanation of this phenomenon. It includes a description of the basic fluid mechanics of SBLIs plus contributions from leading international experts who share their insight into their physics and the impact they have in practical flow situations. This book is for practitioners and graduate students in aerodynamics who wish to familiarize themselves with all aspects of SBLI flows. It is a valuable resource for specialists because it compiles experimental, computational and theoretical knowledge in one place.
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Languages : en
Pages : 0
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This project was aimed at investigating the cause of the low frequency unsteadiness of shock-induced separated flows. This was accomplished by experimentally studying a Mach 5 unswept compression ramp interaction using a combination of planar Imaging diagnostics (namely planar laser scattering and particle image velocimetry (PIV)) and fast response pressure measurements. In particular, PIV was used to investigate the relationship between turbulent velocity fluctuations in the upstream boundary layer and the unsteady separation shock behavior. It was found that positive streamwise velocity fluctuations in the upstream boundary layer correlated with downstream shock motions and negative velocity fluctuations correlated with upstream shock motions. Interestingly, only velocity fluctuations near the wall were correlated with the shock foot motion. These results are coexistent with a simple model wherein a fuller velocity profile provides increased resistance to separation and hence a downstream shock location, and variations in the shape of the velocity profile resulting from turbulent fluctuations yield changes in the shock position and hence produce the unsteady shock foot behavior.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 23
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This project was aimed at understanding the fundamental cause of the low frequency unsteadiness present in shock-induced turbulent separated flows. A new multi-camera, multi-laser PIV system was used to capture wide-field images of the velocity field in a Mach 2 compression ramp interaction. The PIV was acquired simultaneously with fast-response pressure measurements to identify the shock-foot location at the same time that the PIV data were captured. The measurements showed that the global structure of the interaction was substantially different depending on the location of the separation shock foot. For example, when the shock is upstream, the scale of the separated flow, the velocity fluctuations and the domain of perturbed flow, are all substantially larger than when the shock-foot is located downstream. Most importantly, a clear correlation was observed between the thickness and velocity profile in the upstream boundary layer and the shock foot position. A new technique for measuring the upstream boundary layer acceleration by using two-frame time-sequenced PIV was also developed. This involved developing new hardware and software tools, and conducting preliminary calibration experiments. This work has shown the feasibility of correlating the upstream acceleration to the shock motion and these measurements will be made in future work.
Author: Piotr Doerffer
Publisher: Springer
ISBN: 9783642030031
Category : Technology & Engineering
Languages : en
Pages : 336
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Book Description
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.
Author: David Benjamin Helmer
Publisher: Stanford University
ISBN:
Category :
Languages : en
Pages : 212
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Book Description
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.
Author: Center for Turbulence Research (U.S.)
Publisher:
ISBN:
Category : Turbulence
Languages : en
Pages : 410
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Book Description
Author: Raymond A. Humble
Publisher: Eburon Uitgeverij B.V.
ISBN: 9059722957
Category : Organizational change
Languages : en
Pages : 338
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