National Development Agency

From our previous research on the side-load of the LE-7A engine, it was found that a discontinuous step in the nozzle caused large side-load. Fast movement of separation, termed was observed with such large side-load. To clarify the influence of step height and step location on the phenomenon of separation jump and on side-load peak due to the separation jump, a parametric study with cold-flow tests was conducted. Based on the test results, it was clarified that the key phenomenon ruling the separation jump is the base flow behind the step. The influence of design parameters of the step on the separation jump can be explained by the base flow characteristics. The strength of side-load was found to be related only to the location of the step. As the location of the step shifted downstream, the strength of side-load increased. Nomenclature : boundary layer thickness at 70% of nozzle length δ h : step height s x: distance from the throat x : step location s x : position of the separation sep x : distance over which the separation jumps jump L: nozzle length ca NPR: nozzle pressure ratio, P /P NPR : NPR at which nozzle flow separates at each sep position P : ambient pressure around the nozzle a P : stagnation pressure in the chamber c

The cause of 350 Hz large-amplitude rotor vibration of the H-2A rocket's LE-7A fuel turbopump was investigated by wideband oscillating-pressure measurement. Measurement was successfully conducted by quartz-type pressure sensors in full-load liquid-hydrogen tests. The phase difference of pressure oscillations between two pressure measurement ports under conditions of pump cavitating operation revealed a phenomenon similar to rotating stall in turbomachinery which had not been previously observed. The rotating speed of a cell was 350 Hz, about a half the rotor speed. This phenomenon is different from rotating cavitation in which the cavitation pattern rotates around the periphery of an impeller faster than shaft rotating speed. Based on these findings, it was concluded that this phenomenon cased the large-amplitude 350 Hz vibration of the LE-7A fuel turbopump. Results of FFT analysis of measured oscillating pressure are presented.

Concerning a tension-controlled flexible solar paddle, thermomechanical analyses are made to predict maximum/minimum possible temperatures, resulting thermal expansion/contraction lengths, and thermal bending stress generated. Paddle tension-control-mechanism pull-out strokes are then calculated to discuss possibilities of an overstroke that may stress the paddle. Calculated results substaniate the rationality of presumed causes of paddle damage. Strain measurements were also conducted at component/piece/segment levels to determine the paddle equivalent expansion coefficient. Emphasized is that a reasonable estimate of thermal expansion/contraction should be made under temperature-dependent coefficient values.