The design of a cascade wind tunnel for testing of compressor blades at high angle of attack is described. Methods to insure uniform velocity profiles and control of inlet turbulence are discussed. The problem of maintaining two-dimensional flows at high angle of attack was addressed. A tunnel capable of testing cascades of compressor blades at angles of attack up to seventy-five degrees was constructed. Performance of the tunnel was evaluated and data were acquired for flow over double-circular-arc blades with angles of attack extending into the fully-stalled region. Comparisons were made with available data in the installed flow regime. Results showed that the tunnel had adequately uniform inlet velocities and low turbulence levels, and that two-dimensional flow was maintained over the center two-thirds of the high-aspect ratio blades. / Master of Science

This thesis presents an investigation into the motions of the horseshoe vortices and the passage vortex, within a plane turbine blade cascade. Fluid motion was determined using a tracer gas technique. Ethylene was injected into the pressure-side and suction-side legs of the horseshoe vortex, near the leading edge of the cascade. Ethylene concentrations were determined at two downstream locations using a flame ionization detector. It was found that the pressure-side leg of the horseshoe vortex moved toward the suction side of the passage, starting the formation of the passage vortex, and was distributed throughout the passage vortex. The suction-side leg of the horseshoe vortex convected once around the periphery of the passage vortex before passing the cascade trailing edge. Downstream of the trailing edge, most of the fluid from the suction-side leg diffused into the passage vortex. However, twice as much fluid from the suction-side leg, as opposed to the pressure-side leg, mixed within the blade wake. At a location 40% of the axial chord downstream of the trailing edge, the passage vortex (shown previously to account for 60% of the overall total pressure losses) contained over 65% of the fluids from both legs. / M.S.

An investigation has been performed of the flow in a supersonic through-flow fan blade cascade. The blade shapes are those of the baseline supersonic through-flow fan (STFF) under investigation at the NASA Lewis Research Center. Measurements were made at an inlet Mach number of 2.36 over a 15° range of incidence. Flowfield wave patterns were recorded using spark shadowgraph photography and steady-state instrumentation was used to measure blade surface pressure distributions and downstream total and static pressure distributions. A two-dimensional LDV system was used to map the downstream flowfield. From these measurements, the integrated loss coefficients are presented as a function of incidence angle along with analysis indicating the source of losses in the STFF cascade. The results are compared with calculations made using a two-dimensional, cell-centered, finite-volume, Navier-Stokes code with upwind options. Good general agreement is found at design conditions, with lesser agreement at off-design conditions. Analysis of the leading edge shock shows that the leading edge radius is a major source of losses in STFF blades. Losses from the leading edge bluntness are convected downstream into the blade wake, and are difficult to distinguish from viscous losses. Shock losses are estimated to account for 70% to 80% of the losses in the STFF cascade. / Ph. D.

A comprehensive study of the flowfield through a two-dimensional cascade of the high pressure turbine blades of a jet engine is presented. The main interest is the measurement and prediction of the mass-averaged total pressure losses. Other experiments, such as flow visualization, are aimed at the validation of the code that was used to obtain the numerical results and also to further knowledge about the details of the loss generation. The experimental studies were carried out on a cascade of eleven blades in a blow-down tunnel. Total pressure measurements were taken upstream of the cascade and also by traversing on downstream planes. The static pressures needed for the mass averaging and the probe bow shock correction were obtained by pressure taps on the cascade tunnel side wall. The static pressure was also measured on the surface of some instrumented blades. Shadowgraph pictures were taken for study of the trailing edge shock structure and for the turbulent transition location. A single-plate interferometer technique was used for density field measurements. The major goal of the numerical studies was the prediction of the mass-averaged total pressure losses, but all other measured quantities were also generated from the computed flowfield. A critical issue was the generation of a proper grid. For the studied type of flow, a non-periodic C-type grid turned out to be the most advantageous. For use in the moderately compressible attached turbulent boundary layer, a Clauser-type eddy viscosity model was developed and tested. In the trailing edge and wake region, the Baldwin-Lomax model was used. Good agreement of calculations and measurements was obtained for the blade surface and cascade tunnel side wall static pressures, the trailing edge shock structure, and the density field. The agreement between the measured and calculated total pressure drop profiles was not quite as good; however, that quantity is known to be difficult to predict accurately. The mass-averaged total pressure loss coefficient, calculated from the total pressure drop profiles, was again in good agreement with the measurements. The difference between the measured and computed total pressure drop profiles suggested that the Baldwin-Lomax model underpredicted the eddy viscosity in the trailing edge region. / Ph. D.

We examine the dense gas behavior of Bethe-Zel'dovich-Thompson (BZT) fluids in two-dimensional, steady, inviscid, supersonic cascade configurations. Bethe-Zel'dovichThompson fluids are single-phase gases having specific heats so large that the fundamental derivative of gas dynamics, Γ, is negative over a finite range of pressures and temperatures. The equation of state is the well-known Martin-Hou equation, and the numerical scheme is the explicit predictor-corrector method of MacCormack. Numerical comparisons between BZT fluids and more classical fluids such as steam are presented in order to illustrate the possible advantages of using BZT fluids in supersonic cascades. It was found that the natural dynamics of BZT fluids can result in significant reductions in the adverse pressure gradients associated with the collision of compression waves with neighboring turbine blades. A numerical example of an entirely isentropic supersonic cascade flow using a BZT fluid is also presented. / Master of Science

The effects of freestream turbulence on the total pressure and total temperature in the wake of a cooled transonic turbine cascade with heated flow are presented in this thesis. The experiment was conducted in the Virginia Tech Cascade Wind Tunnel. A dual hot wire aspirating probe was used to make high frequency, unsteady total pressure and temperature measurements. The probe design was modified to be used in a high temperature environment. The flow was heated to temperatures exceeding 140°C and the turbine blades were actively cooled using gaseous nitrogen to maintain a gas to blade temperature ratio between 1.3 and 1.4. A turbulence screen was used to change the freestream turbulence from 3.3% to 7.5%. Mean and turbulent total pressure and temperature quantities are presented. The higher freestream turbulence resulted in lower total pressure and total temperature turbulence intensities in the wakes of the turbine blades. The freestream turbulence level had no measurable effect on the blade losses. / Master of Science

An experimental investigation was performed to measure Reynolds stresses in the turbulent flow downstream of a large-scale linear turbine cascade. A rotatable X-wire hot-wire probe that allows redundant data to be taken with solution for mean velocities and turbulence quantities by least-squares fitting procedures was developed. This measurement technique was verified in a fully-developed turbulent pipe flow; the results show the accuracy of the probe when used in an end-flow orientation at various incidence angles and with a multiple number of angular settings. Traverses with a single hot-wire at mid-span near the blade row exit show very high levels of turbulence locally in the blade wake near the trailing edge which quickly lessen in magnitude downstream. The rotatable X-wire was used to obtain the Reynolds stresses on a measurement plane located 10% of an axial chord downstream of the trailing edge. Here the turbulence kinetic energy exhibits a distribution resembling the contours of total pressure loss obtained previously, but is highest in the blade wake where losses are relatively low. The turbulent shear stresses obtained are consistent in sign and magnitude with the gradients of mean velocity. The mass-averaged turbulence kinetic energy accounts for 21% of the total pressure loss at this measurement plane. / Master of Science