Study Of Compressibility Effects Research Articles

A study of compressibility effects on structure of homogeneous sheared turbulence

A study of compressibility effects on structure and evolution of a sheared homogeneous turbulent flow is carried out using rapid distortion theory (RDT). The focus of this paper consists in validating RDT code by considering the direct numerical simulation (DNS) and RDT results of Simone [Simone, Coleman and Cambon, Fluid Mech. 330 , 307 (1997)]. We will use this theory to clarify the physics of the compressible turbulent flows. An analysis of the behavior of different terms appearing in the turbulent kinetic energy and the Reynolds stress equations permit to well identify compressibility effects which allow us to analyze performance of the compressible model of Fujiwara and Arakawa concerning the pressure-dilatation correlation. The evaluation of this model stays in the field of RDT validity.

A study of compressibility effects in the high-speed turbulent shear layer using direct simulation

Direct simulations of the turbulent shear layer are performed for subsonic to supersonic Mach numbers. Fully developed turbulence is achieved with profiles of mean velocity and turbulence intensities that agree well with laboratory experiments. The thickness growth rate of the shear layer exhibits a large reduction with increasing values of the convective Mach number, Mc. In agreement with previous investigations, it is found that the normalized pressure–strain term decreases with increasing Mc, which leads to inhibited energy transfer from the streamwise to cross-stream fluctuations, to the reduced turbulence production observed in DNS, and, finally, to reduced turbulence levels as well as reduced growth rate of the shear layer. An analysis, based on the wave equation for pressure, with supporting DNS is performed with the result that the pressure–strain term decreases monotonically with increasing Mach number. The gradient Mach number, which is the ratio of the acoustic time scale to the flow distortion time scale, is shown explicitly by the analysis to be the key quantity that determines the reduction of the pressure–strain term in compressible shear flows. The physical explanation is that the finite speed of sound in compressible flow introduces a finite time delay in the transmission of pressure signals from one point to an adjacent point and the resultant increase in decorrelation leads to a reduction in the pressure–strain correlation.The dependence of turbulence intensities on the convective Mach number is investigated. It is found that all components decrease with increasing Mc and so does the shear stress.DNS is also used to study the effect of different free-stream densities parameterized by the density ratio, s = ρ2/ρ1, in the high-speed case. It is found that changes in the temporal growth rate of the vorticity thickness are smaller than the changes observed in momentum thickness growth rate. The momentum thickness growth rate decreases substantially with increasing departure from the reference case, s = 1. The peak value of the shear stress, uv, shows only small changes as a function of s. The dividing streamline of the shear layer is observed to move into the low-density stream. An analysis is performed to explain this shift and the consequent reduction in momentum thickness growth rate.

A study of compressibility effects on dynamic stall of rapidly pitching airfoils

Results of recent experimental studies into the effect of compressibility on dynamic stall of oscillating airfoils are reviewed. Stroboscopic schlieren images of the strongly unsteady flow field are presented, showing the development of the dynamic stall vortex, and its progression down the airfoil. The effect of varying free-steam Mach number, and frequency of oscillation of the airfoil are demonstrated, and examples of local supersonic flow are presented, including the presence of a shock near the leading edge of the airfoil.

A precise measurement of the compression of a cylinder in contact with a flat surface

Formulae of interest in precise length metrology for the calculation of the compression of a cylinder loaded against a flat are presented. An apparatus - using air bearings and capacitance probes - for the study of compression effects at surfaces is described and results obtained for the compression of a 6·35 mm diameter steel cylinder in contact over a length of 9·525 mm with a flat in the load range 0·05-0·4 kgf mm−1 are reported. These results are in close agreement with values predicted from a relation based on a finite rectangular area of contact.