Experimental study on correlation between turbulence and sound in a subsonic wind tunnel

Abstract

In this paper, the effects of turbulence on sound generation and velocity fluctuations due to pressure waves in a large subsonic wind tunnel are studied. A trip strip located at different positions in the contraction part or at one position in the diffuser of a large wind tunnel is used to investigate the aforementioned phenomenon, and the results indicate that the trip strip has significant effects on sound reduction. The lowest turbulence intensity and sound are obtained from a trip strip with a diameter of 0.91 mm located either at X/L = 0.79 or at X/L = 0.115 in the wide portion of the contraction. Furthermore, the effect of monopole, dipole and quadrupole sources of aerodynamic noise at different velocities is investigated, and it is demonstrated that the contribution of the monopole is dominant, while the shares due to the dipole and quadrupole remain less important. In addition, it is found that the sound waves have a modest impact on the measured longitudinal turbulence and are generated essentially by eddies. List of symbolsbody force per unit volume P (r, t) instantaneous sound pressure (Pa) ρv i v j , T i j Lighthill tensor (kg·m −2 s −2 ) u 2 ,v 2 second order moments (m 2 ·s −2 ) U p wave propagation speed P sound pressure root mean square (Pa) ρ air density (kg·m −3 ) a 0 free stream sound velocity (m·s −1 ) v u ,u v shear stress tensor (m 2 ·s −2 ) Ma Mach number p pressure fluctuation u p x-component of the longitudinal velocity fluctuation due to the pressure field Cp fluctuating pressure coefficient R = |R| source-observer vector (R = r − r s) T e retarded time (r, t) time and space location of the observer Rs coordinates of the sources ϕ angle between r and r s n i unit normal to the body surface enclosed by S V i fluid velocity components F wall frequency (Hz) k H,n wind tunnel wavenumbers H width (height) of the test section λ H tunnel wavelength 123 532 M. D. Manshadi et al.

CFD and Experimental Study on the Effect of Progressive Heating on Fluid Flow inside a Thermal Wind Tunnel

“…Manshadi et al [16] carried out experimental work on the effects of turbulence generation and velocity fluctuations due to pressure waves in a large low-speed wind tunnel. The study experimentally investigated the relationship between turbulence and generation of sound waves.…”

The Importance of Turbulence Reduction in Assessment of Wind Tunnel Flow Quality

“…The results of this research determine that while the share due to the monopole is dominant, the share due to the dipole and quadrupole remains less important. Furthermore, it is found that sound waves have a modest impact on the measured longitudinal turbulence and is essentially generated by eddies [11]. On the assumptions that first these sound waves are of plane type and contribute only to the u component and second that the turbulence and sound are statistically independent, Uberoi [12] has shown that the spatial correlation coefficient at two different points 1 and 2 for large separation of the points is defined by: …”

“…These parameters are defined according to: The source of turbulence of wind tunnel may briefly divide in two parts; i.e., turbulence due to eddies (vortex shedding, boundary layer, shear stress, secondary flows) and noise (mechanical, vibration and aerodynamic) that There is a correlation between them. Manshadi et-al in [11] studied the effects of turbulence on the sound generation and velocity fluctuations due to pressure waves in a large subsonic wind tunnel. The results of this research determine that while the share due to the monopole is dominant, the share due to the dipole and quadrupole remains less important.…”

“…These pressure waves may enter the test section either from the downstream direction or through the nozzle and thus altering the test condition. Consequently, the lowest velocity fluctuation level in the wind tunnel is determined by the abovementioned pressure fluctuations [11]. i.e.…”

“…i.e. : manshadi et-al in [11] investigated the effect of monopole, dipole, and quadrupole for different turbulence intensity, Fig.5. The turbulence intensity was decreased after trip installation at diffuser and contraction rather than clean condition.…”