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|Title:||Effect of Acoustic Resonance on the Dynamic Lift in Square Tube Arrays|
|Abstract:||An investigation of the dynamic lift on the central tube in square tube arrays is conducted. Three array spacing ratios with P/ D = 3.37, 2.18 and 1.58, corresponding to large, intermediate and small spacing ratios are investigated. These three classes exhibit specific flow characteristics and distinct behavior during acoustic resonance. The aim of the present investigation is to determine the effect of the acoustic pressure field and its contribution to dynamic lift during acoustic resonance. During acoustic resonance there are two sources of dynamic lift. One source is provided by the sound field. The standing wave excited during resonance causes dynamic lift from the acoustic pressure distribution on the surface of the cylinder. In the absence of flow, loud speakers are used to excite the first transverse acoustic mode over a range of sound pressure levels, effectively determining the relationship between the resultant dynamic lift and sound pressure level of the acoustic standing wave. The dynamic lift due to the sound field is well predicted by numerical simulation of the acoustic pressure distribution in the tube array. Using the validated numerical simulation it is possible to extend the results to a large range of cylinder diameter to wavelength ratios. The other source of dynamic lift is provided by the periodic flow though the tube array, known as vortex shedding, which is enhanced during resonance. The total dynamic lift is dependant on the phase shift between the sound field and aerodynamic lift components. For small and intermediate tube arrays, acoustic resonance occurs before coincidence of the natural vortex shedding frequency and the acoustic mode. For the large tube array, frequency coincidence occurs within the resonance range. The phase shift between the dynamic lift due to sound and that due to the aerodynamic lift is small for the pre-coincidence resonance range observed for small and intermediate tube arrays and therefore the total dynamic lift is well predicted by the sum of the magnitudes of the dynamic lift due to the sound field and aerodynamic lift components caused by vortex shedding. Past the frequency of coincidence, a phase jump occurs in the aerodynamic lift causing a large phase shift between the sound field and aerodynamic lift components in the large spacing ratio array. The summation of the aerodynamic lift and the lift due to the sound field over predicts the total dynamic lift measured during acoustic resonance in this case. The present results are used to develop a conservative guideline for estimating the total dynamic lift during acoustic resonance.|
|Appears in Collections:||Digitized Open Access Dissertations and Theses|
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