Raman I Sujith

The purpose of this paper is to present closed form expressions for sound propagation in ducts with polynomial mean temperature profiles. It is shown that using appropriate transformations, the one-dimensional wave equation for ducts with an axial mean temperature gradient can be reduced to a standard differential equation whose form depends upon the specific mean temperature profile in the duct. The solutions are obtained in terms ofBessel and Neumann functions. The analysis neglects the effects of mean flow and therefore the solutions obtained are valid only for mean mach numbers that are less than 0.1. The developed solution is used to investigate the sound propagation in a quarter wave tube with an axial mean temperature gradient. The expressions for the four pole parameters are also presented. © 1998 by ASME.

An exact solution for one-dimensional sound propagation in ducts in the presence of axial mean temperature gradient and particulate damping is presented in this paper. The acoustic wave equation is derived starting from the one-dimensional momentum and energy equation. The application of appropriate transformations leads to an analytically solvable Whittaker's differential equation for the case of a linear mean temperature gradient and Bessel's differential equation for the case of an exponential mean temperature gradient. The derived analytical solutions are used to investigate the dependence of the acoustic field in a duct on temperature gradient and particulate damping.

This paper reports about a preliminary investigation on the characteristics of acoustic radiation by a two-dimensional confined supersonic flow past a wall-mounted cavity. Rectangular cavities of nine different L/D ratios were considered: three “deep”, three “shallow'’ and three “square” shapes. Inlet Mach numbers of 1.5 and 2.0 were tested. Results obtained are in the form of (a) acoustic measurements at different locations on the wall of the test section opposite to the cavity wall and (b) visualisation of the flow in and around the cavity. A wide range of acoustic amplitudes was recorded at different locations with different cavities. The results help in the identification of cavity shapes that are most suited for further consideration in future studies on mixing, secondary fuel injection, and combustion. The visualisation experiments suggest more locations corresponding to oscillating shocks where acoustic amplitudes could be larger than recorded so far.

The objective of this paper is to present exact analytical solutions for the longitudinal vibration of rods with non-uniform cross-section. Using appropriate transformations, the equation of motion of axial vibration of a rod with varying cross-section is reduced to analytically solvable standard differential equations whose form depends upon the specific area variation. Solutions are obtained for a rod with a polynomial area variation and for a sinusoidal rod. The solutions are obtained in terms of special functions such as Bessel and Neumann as well as trignometric functions. Simple formulas to predict the natural frequencies of non-uniform rods with various end conditions are presented. The natural frequencies of non-uniform rods for these end conditions are calculated, and their dependence on taper is discussed. The governing equation for the problem is the same as that of wave propagation through ducts with non-uniform cross-sections. Therefore solutions presented here can be used to investigate such problems. © 1997 Academic Press Limited.

A detailed experimental investigation of freejets and their impinging flowfields has been carried out. Studies were conducted for different pressure ratios, and the influence of Reynolds number on flow freezing was examined. A conical convergent-divergent nozzle of large area ratio, typically employed in aerospace applications, was used in the studies. Quantitative data of freejet and impingement flowfields, which could be used as a benchmark for checking the results obtained from numerical simulations such as the direct simulation Monte Carlo method, are presented. Forces due to plume impingement on an adjacent surface were estimated. The impingement effects were found to be considerable at high Reynolds numbers, whereas flowfield properties were found to be unaffected due to the presence of the plate at low Reynolds numbers. The freejet and the impinging flowfield were visualized using a glow discharge technique. The features of transition flow were observed in low Reynolds number flows. The flowfield modifications brought about by the influence of the flat plate could also be visualized.

The purpose of this Letter is to present an exact analytical solution for sound propagation in ducts with a quadratic mean temperature profile. Using appropriate transformations, the one-dimensional wave equation for ducts with an axial mean temperature gradient was reduced to the hypergeometric differential equation, whose solution can be expressed in terms of hypergeometric functions. The analysis neglects the effects of mean flow and is therefore valid only for small mean Mach numbers.

Turbulent premixed combustion, while of increased practical importance, is still not fully understood. A serious barrier to further progress in this area lies in the fact that at the high Reynolds numbers encountered in most turbulent reacting flows the Kolmogorov scale is too small to resolve experimentally. When tests at lower Reynolds number are run, the effects of buoyancy become important. In the present study the effect of buoyancy is removed from a turbulent Couette flow by testing it under conditions of microgravity. In the work reported here the velocity field of the cold flow under normal gravity forces was fully characterized. The feasibility of using acetone planar laser induced fluorescence to measure turbulent passive scalar diffusion was confirmed. It was determined that the full range of turbulence scales could be observed experimentally for Reynolds numbers of interest in subsequent combustion studies.