Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 129
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Book Description
A fully-developed high Reynolds number Mach 3 turbulent boundary layer and the effects of four expansion regions (centered and gradual expansions of 7 deg and 14 deg) on the boundary layer were investigated by utilizing 1) multi-point instantaneous surface pressure measurements, 2) instantaneous single- and double-pulse flow visualizations based on Filtered Rayleigh Scattering (FRS), 3) two-component planar velocity measurements using Filtered Planar Velocimetry (FPV), and 4) detailed turbulence measurements using Laser Doppler Velocimetry (LDV). Flow visualization results indicate that the upper half of the fully developed turbulent boundary layer is populated with elongated longitudinal structures of considerable streamwise but very limited spanwise extent. These structures are randomly distributed in space and time and survive even the 14 deg centered expansion. The visualizations also show that large scale structures increase both in size and angle and small scale structures are quenched across the expansions. The angle of large scale structures return to the flat plate value further downstream of the expansions. The normalized power spectra of pressure fluctuations downstream of the expansions are more concentrated at lower frequencies than their upstream counterparts, confirming the small scale quenching shown by flow visualizations.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 191
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Book Description
The effects of various expansion regions on the large scale structure of a Mach 3 fully-developed-turbulent boundary layer are investigated. Five cases are studied: 7 deg and 14 deg centered expansions, 7 deg and 14 deg gradual expansions, and the flat plate. Multi-point surface pressure measurements, filtered Rayleigh scattering visualizations, and double-pulse visualizations were employed. Plan view images of the flat plate boundary layer reveal the presence of structures of a very large streamwise, and limited spanwise, extent. These structures were found well above the inner layer, nominally at n/delta = 0.5-1.0. The structures were also found in the expanded boundary layers. Across the expansion, the large scale structures of the outer layer undergo an increase in scale and structure angle. The small scale turbulent motions of the incoming boundary layer are quenched by the expansion, while the large scale structures respond more gradually. Convection velocities from the pressure correlations are reasonable in the incoming boundary layer, but unreasonably high in the expanded boundary layers. Convection velocities from correlations of double-pulse images appear reasonable. The discrepancy between the two results suggests the relationship between the large scale structures and the convecting pressure field is severely altered by the expansions.
Author: Stephen Andrew Arnette
Publisher:
ISBN:
Category :
Languages : en
Pages : 774
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Book Description
Author: Alexander J. Smits
Publisher: Springer Science & Business Media
ISBN: 0387263055
Category : Science
Languages : en
Pages : 418
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Book Description
A good understanding of turbulent compressible flows is essential to the design and operation of high-speed vehicles. Such flows occur, for example, in the external flow over the surfaces of supersonic aircraft, and in the internal flow through the engines. Our ability to predict the aerodynamic lift, drag, propulsion and maneuverability of high-speed vehicles is crucially dependent on our knowledge of turbulent shear layers, and our understanding of their behavior in the presence of shock waves and regions of changing pressure. Turbulent Shear Layers in Supersonic Flow provides a comprehensive introduction to the field, and helps provide a basis for future work in this area. Wherever possible we use the available experimental work, and the results from numerical simulations to illustrate and develop a physical understanding of turbulent compressible flows.
Author: Mingbo Sun
Publisher: Springer Nature
ISBN: 9811535957
Category : Technology & Engineering
Languages : en
Pages : 380
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Book Description
This book describes the unsteady phenomena needed to understand supersonic combustion. Following an initial chapter that introduces readers to the basic concepts in and classical studies on unsteady supersonic combustion, the book highlights recent studies on unsteady phenomena, which offer insights on e.g. interactions between acoustic waves and flames, flow dominating instability, ignition instability, flame flashback, and near-blowout-limit combustion. In turn, the book discusses in detail the fundamental mechanisms of these phenomena, and puts forward practical suggestions for future scramjet design.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 115
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Book Description
The effect of a favorable pressure gradient on the turbulent flow structure in a Mach 2.9 boundary layer (Re/m approx. 1.5 x 10(exp 7)) is investigated experimentally. Conventional flow and hot film measurements of turbulent fluctuation properties have been made upstream of and along an expansion ramp. Upstream measurements were taken in a zero pressure gradient boundary layer 44 cm from the nozzle throat in a 6.35 cm square test section. Measurements are obtained in the boundary layer, above the expansion ramp, 71.5 cm from the nozzle throat. Mean flow and turbulent flow characteristics are measured in all three dimensions. Comparisons are made between data obtained using single and multiple-overheat cross-wire anemometry as well as conventional mean flow probes. Conventional flow measurements were taken using a Pitot probe and a 10 degree cone static probe. Flow visualization was conducted via imaging techniques (Schlieren and shadowgraph photographs). Results suggest that compressibility effects, as seen through the density fluctuations in the Reynolds shear stress are roughly 10% relative to the mean velocity and are large relative to the velocity fluctuations. This is also observed in the total Reynolds shear stress; compressibility accounts for 50 - 75% of the total shear. This is particularly true in the favorable pressure gradient region, where though the peak fluctuation intensities are diminished, the streamwise component of the mean flow is larger, hence the contribution of the compressibility term is significant in the Reynolds shear.
Author: P. H. Oosthuizen
Publisher:
ISBN:
Category : Aerodynamics, Supersonic
Languages : en
Pages : 41
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Book Description
A theoretical study of the effects of the wall boundary layer on the supersonic flow around a sharp convex corner is presented. Fundamentally different methods of analysis are adopted for laminar and for turbulent boundary layers. In the case of interactions involving laminar boundary layers, an analysis based on the use of classical boundary layer theory is used. Results of numerical calculations carried out using this analysis to predict the effects of the major governing parameters are presented. In all cases, a considerable upstream and downstream influence is predicted. A simplified form of this analysis, closely related to that of Curle, is also presented, this analysis leading to a simple set of explicit equations describing the flow quantities in the interaction region. Comparison of the simplified analysis with results obtained from the full analysis indicated, as is to be expected, that the simplified analysis will only give acceptable results for small expansion angles and moderate Mach numbers. In the case of turbulent boundary layer interactions, an analysis based on the assumption that there is no upstream influence and that the major portion of the expansion occurs in an effectively inviscid manner is adopted, the flow properties being calculated by the method of rotational characteristics. (Author).
Author: Alexander J. Smits
Publisher:
ISBN:
Category : Boundary layer
Languages : en
Pages : 76
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Book Description
Author: Thomas B. Gatski
Publisher: Elsevier
ISBN: 0080559123
Category : Science
Languages : en
Pages : 296
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Book Description
This book introduces the reader to the field of compressible turbulence and compressible turbulent flows across a broad speed range through a unique complimentary treatment of both the theoretical foundations and the measurement and analysis tools currently used. For the computation of turbulent compressible flows, current methods of averaging and filtering are presented so that the reader is exposed to a consistent development of applicable equation sets for both the mean or resolved fields as well as the transport equations for the turbulent stress field. For the measurement of turbulent compressible flows, current techniques ranging from hot-wire anemometry to PIV are evaluated and limitations assessed. Characterizing dynamic features of free shear flows, including jets, mixing layers and wakes, and wall-bounded flows, including shock-turbulence and shock boundary-layer interactions, obtained from computations, experiments and simulations are discussed. Describes prediction methodologies including the Reynolds-averaged Navier Stokes (RANS) method, scale filtered methods and direct numerical simulation (DNS) Presents current measurement and data analysis techniques Discusses the linkage between experimental and computational results necessary for validation of numerical predictions Meshes the varied results of computational and experimental studies in both free and wall-bounded flows to provide an overall current view of the field
Author: William A. Cassels
Publisher:
ISBN:
Category : Aerodynamics, Supersonic
Languages : en
Pages : 76
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Book Description
Boundary-layer transition by the sublimation and impact-pressure techniques and force tests have been performed on three Haack-Adams bodies of revolution of fineness ratios 7, 10, and 13 at zero angle of attack for free-stream Mach numbers of 2.00, 2.75, and 4.63 and a range of Reynolds numbers based on model length of 6 to 15 X 10(to the 6 power) with and without a roughness strip. The grit method of inducing turbulence was found to provide for a nearly complete turbulent flow over the models at the lower Mach numbers and higher Reynolds numbers considered in this study while the amount of trip drag was less than 8 percent of the model drag with transition fixed. A method of interpreting sublimation data was discussed and used and the results compared well with the impact-pressure results.
