Experimental measurement of inlet mass flow of a microjet engine and performance parameters with a five-hole probe

摘要

Micro jet engines have broad applications to light air vehicles such as light and ultralight sports planes, sailplanes, piloted vehicles of experimental class and various unmanned air vehicles. The performance test of microjet engines is necessary to ensure that the manufacturer meets performance predictions. In addition, it is vital to monitor the operating range of micro jet engines after an upgrade, maintenance, or physical system change. In the category of small jet engines, the AMT Olympus jet turbine was tested with thrust up to 230 N and maximum speed of 112000 rpm, which is among the best high performance jet engines. In this work, theperformance parameters of the micro jet in steady-state conditions was measured in an indoor test cell. The measured parameters include pressure ratio, temperature, thrust, specific fuel consumption, and engine speed. In addition, we measured flow parameters of the micro jet for three different engine speeds as follows: velocity, pitch angle, yaw angle, static pressure, total pressure and mass flow rates. These parameters were measured at different distances from the jet centerline. Due to the complexity of the flow field, a five-hole probe with a 60 degree cone angle was designed to measure the flow angle and magnitude of velocity at the inlet of the micro jet engine. The non-nulling method was applied for the calibration process of the probe in a wind tunnel and generated calibration coefficients as well as flow angle ranges. We analyzed the data to determine the inlet pressure profile in a low-Reynolds number flow field. The equations for total pressures at each of the five holes of the probe were derived for given pitch and yaw angles that were varied from -25° to 25° during calibration. The measured calibration coefficients were then used to measure properties of the flow generated by the micro jet engine. Finally, the total pressure was also measured using a pressure rake at various points along the diameter of the test section. By the comparison of average total pressures measured by the five-hole probe and the rake it was found that the rake pressures are significantly lower than the corresponding probe pressures. The difference is attributed to the secondary flow sensed by the rake.