Free underexpanded jets in a quiescent medium: A review

.................................................................................................... xxxii Chapter

The Influence of Neutral Flow Rate in the Operation of Hall Thrusters.

New experimental data are used to show that the direct simulation Monte Carlo (DSMC) method provides an accurate description of a low-density flow in the nozzle and the near-field expansion of a small rocket for two slightly different experimental configurations. These results verify the DSMC method in an expansion flow for the first time. From a number of different gas/surface interaction models, it is found that fully diffuse reflection gives the best agreement with experiment.

Experimental and numerical investigations of low-density nozzle and plume flows of nitrogen

The quasi-one-dimensionalequations of  uid motion are coupled with the equations for  nite-rate chemistry to model high-speed engine  ow elds. The model was developed for rapid vehicle design and optimization, where a wide range of engine inlet conditionsmay be encountered. Incorporating the timescales of fuel mixing and ignition are crucial for accurate prediction of combustor performance, especially for nonhydrogen fuels and off-design conditions (where equilibrium assumptions are invalid). The effects of area change, friction, mass injection, fuel mixing, and heat transfer to the combustor walls are included. The resulting model is compared to experimental results for hydrogen-fueled scramjet engines to demonstrate the ability to predict wall pressure pro les and fuel ignitionpoint. Application to a rocket-based combined-cycle engine and a hydrocarbon scramjet missile engine are discussed. The model presented predicts peak pressure and fuel ignition accurately, as well as  ow eld pressures in regions where boundary-layer separation is not present.

Quasi-One-Dimensional High-Speed Engine Model with Finite-Rate Chemistry

A hybrid particle approach for continuum and rarefied flow simulation

Reduced reaction mechanisms for numerical calculations in combustion of hydrocarbon fuels

Core noise from a YF-102 high bypass ratio turbofan engine was investigated through the use of simultaneous measurements of internal fluctuating pressures and far field noise. Acoustic waveguide probes, located in the engine at the compressor exit, in the combustor, at the turbine exit, and in the core nozzle, were employed to measure internal fluctuating pressures. Spectra showed that the internal signals were free of tones, except at high frequency where machinery noise was present. Data obtained over a wide range of engine conditions suggest that below 60% of maximum fan speed the low frequency core noise contributes significantly to the far field noise.

/pdf/core-noise-measurements-on-a-yf-102-turbofan-engine-kezsrc89kt.pdf

Core Noise Measurements on a YF-102 Turbofan Engine

Tests were conducted to investigate the effect of vacuum facility pressure on the performance of small thruster nozzles. Thrust measurements of two converging-diverging nozzles with an area ratio of 140 and an orifice plate flowing unheated nitrogen and hydrogen were taken over a wide range of vacuum facility pressures and nozzle throat Reynolds numbers. In the Reynolds number range of 2200 to 12 000 there was no discernable viscous effect on thrust below an ambient to total pressure ratio of 1000. In nearly all cases, flow separation occurred at a pressure ratio of about 1000. This was the upper limit for obtaining an accurate thrust measurement for a conical nozzle with an area ratio of 140.

/pdf/vacuum-chamber-pressure-effects-on-thrust-measurements-of-43fzsrfpib.pdf

Vacuum chamber pressure effects on thrust measurements of low Reynolds number nozzles

Tests were conducted to investigate the effect of ambient pressure on the measured thrust of a prototype resistojet. The tests were performed using both heated and unheated nitrogen as the propellant at flow rates of 0.0379 and 0.0759 g/s. For the cold flow tests there was no effect on specific impulse over a range of ambient pressures from 1 to 400 microns. The results for the hot flow tests did show as much as a 7 percent variation in specific impulse over the same range of ambient pressures.

Paul F. Penko

Papers

Experimental and numerical investigations of low-density nozzle and plume flows of nitrogen

Reduced reaction mechanisms for numerical calculations in combustion of hydrocarbon fuels

Core Noise Measurements on a YF-102 Turbofan Engine

Vacuum chamber pressure effects on thrust measurements of low Reynolds number nozzles

Effect of ambient pressure on the performance of a resistojet