Comparison of engine/inlet distortion measurements with MEMS and ESP pressure sensors

A study of active-flow control in a small-scale boundary layer ingestion inlet was conducted at the NASA Langley Basic Aerodynamic Research Tunnel (BART). Forty MEMS pressure sensors, in a rake style configuration, were used to examine both the mean (DC) and high frequency (AC) components of the total pressure across the inlet/engine interface plane. The mean component was acquired and used to calculate pressure distortion. The AC component was acquired separately, at a high sampling rate, and is used to study the unsteady effects of the active-flow control. An identical total pressure rake, utilizing an Electronically Scanned Pressure (ESP) system, was also used to calculate distortion; a comparison of the results obtained using the two rakes is presented. Introduction The efficiency of an aircraft’s engine is greatly impacted by its placement on the surface of the vehicle. In NASA’s design of the Blended Wing Body (BWB), the optimal location for engines and inlets is near the upper surface on the aft section of the vehicle. Unfortunately, incorporation of the inlet on the surface of the vehicle increases the technical risk of the configuration. The NASA Ultra Efficient Engine Technology (UEET) program chose to pursue the use of boundary layer ingestion (BLI) inlets with an active flow control system for the BWB design to reduce this risk. Different inlets have been studied, from semi-elliptical geometries ingesting boundary layers with a height on the order of 30% of the inlet diameter to rectangular inlets ingesting 150% of the airfoil’s boundary layer height. It has been shown that the use of these inlet designs may potentially increase the aircraft’s cruising distance by 10%, if one was able to control the adverse effects of this design in terms of distortion and pressure recovery. The inlet presented in this study incorporates a cylindrical s-inlet with 30% BLI. The UEET program has been studying different methods to reduce the distortion caused by the aforementioned BLI inlet. In this test, an active flow control system utilizing high-pressure air was positioned upstream of the engine inlet to control pressure distortion. This method was shown to reduce the 29% baseline distortion value to around 7% as measured using the DC60 calculation method. This paper presents the results of using MEMS pressure sensors to measure the total pressure used to calculate distortion, and how these results compare to the wind tunnel standard ESP systems. Additionally, the MEMS sensors are used to measure the high frequency response of the flow when the active flow control system was in operation, with the main objective being to observe the effects of the jets or the active flow control system at the engine/inlet interface. ∗ Research Engineer, Advanced Model and Sensor Systems Branch † Research Engineer, Advanced Sensing and Optical Measurements Branch