Experimental and Theoretical Studies of Axisymmetric Free Jets


Book Description

Some experimental and theoretical studies have been made of axisymmetric free jets exhausting from sonic and supersonic nozzles into still air and into supersonic streams with a view toward problems associated with propulsive jets and the investigation of these problems. For jets exhausting into still air, consideration is given to the effects of jet Mach number, nozzle divergence angle, and jet static-pressure ratio upon jet structure, jet wavelength, and the shape and curvature of the jet boundary. Studies of the effects of the ratio of specific heats of the jets are included as are observations pertaining to jet noise and jet simulation. For jets exhausting into supersonic streams, an attempt has been made to present primarily theoretical curves of the type that may be useful in evaluating certain jet interference effects and in formulating experimental studies. The primary variables considered are jet Mach number, free-stream Mach number, jet static-pressure ratio, ratio of specific heats of the jet, nozzle exit angle, and boattail angle. The simulation problem and the case of a hypothetical hypersonic vehicle are examined. A few experimental observations are included.




Direct Numerical Simulation of Axisymmetric Jets


Book Description

We present results from numerical simulations of the evolution of the Kelvin-Helmholtz instability for an unforced, subsonic, compressible axisymmetric, spatially-evolving shear layer. In addition, we study the effect of small, random pressure fluctuations at the nozzle orifice on the growth of the mixing layers. These fluctuations model inflow perturbations in experimental flows arising from turbulence and boundary layers in the nozzle. The finite-difference numerical model used to perform the simulations solves the two-dimensional time-dependent conservation equations for an ideal fluid using the Flux-Corrected Transport algorithm and timestep-splitting techniques. No subgrid turbulence model has been included. In the absence of perturbations, the calculations indicate that the large scale development of the unforced jet shear layer has an underlying degree of organization. This is the result of a feedback mechanism in which the shear layer ahead of nozzle edge is modulated by the far field induced gy the mergings on downstream, near the end of the potential core of the jet. The studies with random high frequency perturbations on the inflow velocity show that they effectively tend to break the temporal correlations between the structures. Keywords: Coherent structures; Free Shear flows.







Acoustic Control of Turbulent Jets


Book Description

Results of experimental research on aerodynamic and acoustic control of subsonic turbulent jets by acoustic excitation are presented. It was demonstrated that these control methods, originated by authors, not only can intensify mixing (by acoustic irradiation at low frequency), but also notably ease it (at high-frequency irradiation). This research monograph presents the updated results of the authors supplemented by other investigations conducted in USA, Germany and Great Britain. The methods for the numerical simulation of subsonic turbulent jets under acoustic excitation are described in detail, and examples are reviewed of practical applications, including reduction of turbojet engine noise and acoustic control of self-sustained oscillations in wind tunnels.




Transition, Turbulence and Combustion


Book Description

These two volumes contain the proceedings of the Workshop on Transition, Turbulence and Combustion, sponsored by the Insti tute for Computer Applications in Science and Engineering (ICASE) and the NASA Langley Research Center (LaRC), during June 7 to July 2, 1993. Volume I contains the contributions from the transi tion research, and Volume II contains the contributions from both the turbulence and combustion research. This is the third workshop in the series on the subject. The first was held in 1989, the second in 1991, and their proceedings were published by Springer-Verlag under the titles "Instability and Transition" (edited by M. Y. Hussaini and R. G. Voigt) and "Instability, Transition and Turbulence" (edited by M. Y. Hussaini, A. Kumar and C. L. Streett) respectively. The objectives of these workshops are to expose the academic community to current technologically important issues of transition, turbulence and combustion, and to acquaint the academic commu nity with the unique combination of theoretical, computational and experimental capabilities at LaRC. It is hoped these will foster con tinued interactions, and accelerate progress in elucidating the funda mental phenomena of transition, turbulence and combustion. The research areas of interest in transition covered the full range of the subject: linear and nonlinear stability, direct and large-eddy simulation and phenomenological modeling of the transition zone.













87-0050-87-0099


Book Description