For decades large amounts of money and effort have been spent on conventional turbomachinery development. Initially improvements in performance were rapid. However, in the last two decades better performance of these machines has slowed considerably. Compressor efficiencies have been near their present limits of 88% to 92% for many years. High pressure ratios required of high performance engines are not efficiently produced in the conventional turbomachines. High pressure ratios for high cycle efficiency require many stages of conventional compression. Compressors, especially in small turbomachines, decrease in efficiency as the number of stages increase due to the large amounts of surface area and relatively large leakage passages in the higher pressure stages. The requirement for many stages of conventional compression also results in heavy machines. If high compressor pressure cannot be attained the turbine exhaust gas temperature may be considerably above the compressor discharge temperature; a regenerator or recuperator is then required for acceptable cycle efficiency. This results in considerable complication and high engine weight. Maximum turbine inlet temperatures in conventional machines have also been near their limit for many years. High temperatures and high pressures required for light weight, high efficiency machines are inconsistent with the requirements for high strength materials. To increase permissable turbine inlet temperatures compressor discharge air is used for blade cooling. Use of this air soon reaches its limit because the high pressure cooling air is then not available for power production. Engine power and cycle efficiency begins to decrease and a limit on turbine inlet temperature results. Consequently, new concepts in power and thrust production are required. One class of machines which may alleviate many of the above described problems are the wave rotors or engines (1 thru 15). These operate with time dependent flow in the moving rotor blade passages and steady flow in the stator parts.
A simple, semiempirical method for calculating the laminar, transition, and turbulent boundary layer with arbitrary free stream pressure gradient is developed. Good correlation is obtained with data on general two dimensional turbulent flows, diffuser flows, and the cylinder in cross-flow. However only for the diffuser has the boundary layer flow been coupled with the potential core so that only the inlet conditions and geometry are required. In other cases the free stream velocity distribution must be known or calculable. Skin friction coefficient, momentum thickness Reynolds number, and free stream pressure gradient parameter correlation employs a simple lag theory. With the integral momentum equation the complete boundary layer parameters are obtained as functions of the distance along a surface.
A method for aerothermodynamic preliminary design of a wave engine is presented. The engine has a centrifugal precompressor for the wave rotor, which feeds high and low-pressure turbines. Three specific wave engine designs are presented. Wave rotor blades are naturally cooled by the ingested air; thus combustion temperatures can be as high as 1900 K. Engine pressure ratios of over 25 are obtained in compact designs. It is shown that placing no nozzles at the end of the rotor blade passages yields the highest cycle efficiencies, which can be over 50 percent. Rotor blades are straight and easily milled, cast, or fabricated.
A theory for the prediction of flow for fully choked divergent shroud nozzles has been compared with experiment and corrected empirically. The prediction of thrust has been extended to include both the underexpanded and overexpanded flow regimes in this type of nozzle. Comparisons with the theory have been made and good correlation found in both overexpanded and underexpanded regimes of flow.
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