ACTIVE CONTROL OF PRESSURE FLUCTUATIONS DUE TO FLOW OVER HELMHOLTZ RESONATORS
✍ Scribed by H. KOOK; L. MONGEAU; M.A. FRANCHEK
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 545 KB
- Volume
- 255
- Category
- Article
- ISSN
- 0022-460X
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✦ Synopsis
Grazing #ows over Helmholtz resonators may result in self-sustained #ow oscillations at the Helmholtz acoustic resonance frequency of the cavity system. The associated pressure #uctuations may be undesirable. Many solutions have been proposed to solve this problem including, for example, leading edge spoilers, trailing edge de#ectors, and leading edge #ow di!users. Most of these control devices are &&passive'', i.e., they do not involve dynamic control systems. Active control methods, which do require dynamic controls, have been implemented with success for di!erent cases of #ow instabilities. Previous investigations of the control of #ow-excited cavity resonance have used mainly one or more loudspeakers located within the cavity wall. In the present study, oscillated spoilers hinged near the leading edge of the cavity ori"ce were used. Experiments were performed using a cavity installed within the test section wall of a wind tunnel. A microphone located within the cavity was used as the feedback sensor. A loop shaping feedback control design methodology was used in order to ensure robust controller performance over varying #ow conditions. Cavity pressure level attenuation of up to 20 dB was achieved around the critical velocity (i.e., the velocity for which the fundamental excitation frequency matches the Helmholtz resonance frequency of the cavity), relative to the level in the presence of the spoiler held stationary. The required actuation e!ort was small. The spoiler peak displacement was typically only 4% of the mean spoiler angle (approximately 13). The control scheme was found to provide robust performance for transient operating conditions. Oscillated leading edge spoilers o!er potential advantages over loudspeakers for cavity resonance control, including a reduced encumbrance (especially for low-frequency applications), and a reduced actuation e!ort.