Experimental Investigation of a Missile Forebody Acoustics Flow Field in a Transonic Wind Tunnel

Abstract

A wind tunnel test to investigate and characterize potential aeroacoustics sources of high frequency vibration which may stimulate critical sensitivities of the Inertial Measurement Unit (IMU), resulting in errant response stability of a missile, has been performed in the Lockheed Martin 4-Ft High Speed Wind Tunnel (HSWT), Dallas, TX. Three main areas of potential acoustics sources on the missile forebody, using high frequency pressure transducers strategically positioned around the areas of interest, were investigated: ogive nose, four canard slots, and four canards. Since it was anticipated that the acoustics flow field generated by the model would be seriously contaminated by the wind tunnel background noise, static pressure fluctuations calibration, using a newly designed ten-degree cone was executed before the test at the Mach number range of 0.7 to 1.3. The wind tunnel background noise calibration was performed in both perforated and solid wall wind tunnel test sections. It was found that, in spite of the fact that all the model forebody components; i.e., ogive nose, canard slots, and canards generated a significant level of acoustical disturbances at various discrete frequencies, the model itself did not generate a high enough acoustics energy level to influence the angular output from the IMU. However, the tunnel; i.e., edge-tones generated by the perforated test section walls, produced a sufficient acoustics energy level that prevented any useful angular reading. This finding underlines the importance of separating the model and wind tunnel aeroacoustics flow fields for any type of aeroacoustics investigation in wind tunnels, since the “contaminated” model aeroacoustics environment can generate misleading results.