This work is an extension of a project conducted at the previous CTR summer program and was reported by Chen et el. (1990). In that program, the geometry and topology of the dissipating motions in a variety of shear flows was examined. All data was produced by direct numerical simulations (DNS). The partial derivatives of the velocity field were determined at every grid point in the flow and various invariants and related quantities were computed from the velocity gradient tensor. Motions characterized by high rates of kinetic energy dissipation and high enstrophy were of particular interest.Scatter diagrams of the invariants were mapped out and interesting and unexpected patterns were seen. Each type of shear layer produced its own characteristic scatter plot.In the present project, attention is focused on the incompressible plane mixing layer, and the scatter diagrams are replaced with more useful joint probability density contours.Comparison of the topology of the dissipating motions of flows at different Reynolds numbers are made.Also, plane mixing layers at the same Reynolds number but with different initial conditions are compared. Method of approachThe velocity gradient tensor may be broken up into a symmetric and an antisymmetric part Aij = Oui/Ox) = Sij + Wij where Sij = (Oui/Oxj + Ouj/Oxi)/2 and Wij = (Oui/Oxj -OuffOxi)/2 are the rate-of-strain and rate-of-rotation tensors, respectively.The eigenvalues of Aij satisfy the characteristic equationwhere the matrix invariants are:

Recent years have seen a substantial increase of interest in the flows of granular materials whose rheology is dominated by the physical contact between particles and between particles and the containing walls. Considerable advances in the theoretical understanding of rapid granular material flows have been made by the application of the statistical methods of molecular gas dynamics (e.g., Jenkins and Savage (1983), Lun et al. (1984)) and by the use of computers simulations of these flows (e.g., Campbell and Brennen (1985), Walton (1984)). Experimental studies aimed at measurements of the fundamental rheology properties are much less numerous and are understandably limited by the great difficulties involved in trying to measure velocity profiles, solid fraction profiles, and fluctuating velocities within a flowing granular material. Nevertheless, it has become clear that one of the most severe Measurements of r Bouncing Off Flat Plate problems encountered when trying to compare experimental data with the theoretical models is the uncertainty in the material properties governing particle/particle or particle/wall collisions. Many of the theoretical models and computer simulations assume a constant coefficient of restitution (and, in some cases, a coefficient of friction). The purpose of the present project was to provide some documentation for particle/wall collisions by means of a set of relatively simple experiments in which solid spheres of various diameters and materials were bounced off plates of various thickness and material. The objective was to provide the kind of information on individual particle/wall collisions needed for the theoretical rheological models and computer simulations of granular material flows: in particular, to help resolve some of the issues associated with the boundary condition at a solid wall. For discussion of the complex issues associated with dynamic elastic or inelastic impact, reference is made to Goldsmith (1960) and the recent text by Johnson (1985).

The application of pulsed vortex generator jets to control separation on the suction surface of a low pressure turbine blade is reported. Blade Reynolds numbers in the experimental, linear turbine cascade match those for high altitude aircraft engines and aft stages of industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets have a 30 degree pitch and a 90 degree skew to the freestream direction. Jet flow oscillations up to 100 Hz are produced using a high frequency solenoid feed valve. Results are compared to steady blowing at jet blowing ratios less than 4 and at two chordwise positions upstream of the nominal separation zone. Results show that pulsed vortex generator jets produce a bulk flow effect comparable to that of steady jets with an order of magnitude less massflow. Boundary layer traverses and blade static pressure distributions show that separation is almost completely eliminated with the application of unsteady blowing. Reductions of over 50% in the wake loss profile of the controlled blade were measured. Experimental evidence suggests that the mechanism for unsteady control lies in the starting and ending transitions of the pulsing cycle rather than the injected jet stream itself. Boundary layer spectra support this conclusion and highlight significant differences between the steady and unsteady control techniques. The pulsed vortex generator jets are effective at both chordwise injection locations tested (45% and 63% axial chord) covering a substantial portion of the blade suction surface. This insensitivity to injection location bodes well for practical application of pulsed VGJ control where the separation location may not be accurately known a priori.

The application of vortex-generator jets to control separation on the suction surface of a low-pressure turbine blade is reported. Blade Reynolds numbers in the experimental, linear turbine cascade match those for high-altitude operation of many aircraft gas-turbine engines, as well as the last stages of industrial ground-based gas turbines. Results are presented for steady blowing at jet blowing ratios from zero to four and at several chordwise positions and two freestream turbulence levels. Findings show that above a minimum blowing ratio, which is dependant on the injection location, the pressure loss in the modi ed blade's wake is reduced by a factor of between two and three. Boundary-layer traverses show that separation isalmost completely eliminated with the application of blowing. No signi cant deleterious effects of vortex-generator jets are observed at higher (nonseparating) Reynolds numbers. The addition of 4% freestream turbulence to the cascade freestream lowers the separation Reynolds number of the turbine blade studied, but does not eliminate the effectiveness of the control technique. The vortex-generator jet control strategy is demonstrated to be a viable technique for low-pressure turbine separation control. Nomenclature B = jet blowing ratio, .½u/ jet =.½u/ loc C x = axial chord length, 17.8 cm c d = jet hole discharge coef cient c p = blade pressure coef cient . p t;i ¡ p loc /=q i d = jet hole diameter, 1 mm L = blade loading parameter [see Eq. (1)] l = jet hole length, 8 mm p = pressure, Pa q = dynamic pressure, ½u 2 =2, Pa Re = inlet Reynolds number, ½ i u i C x =¹ T u = freestream turbulence in percent u = streamwise mean velocity, m/s u 0 = streamwise rms uctuating velocity, m/s°= blade pressure loss coef cient, . p t;i ¡ N p t;o /=q i°l oc = local blade pressure loss coef cient, . p t;i ¡ p t;loc /=q i ¹ = dynamic viscosity, kg/m s ½ = density, kg/m 3 Subscripts i = cascade inlet conditions, reference jet = vortex-generatorjet conditions loc = local blade midchannel conditions o = cascade outlet conditions t = stagnation or total conditions Superscript ¡ = pitch-averaged quantity