Effect of thickness on airfoil surface noise

Leading Edge Noise from Thick Foils in Turbulent Flows

“…The spatial domain formulation of the blade vortex interaction (BVI) models of Martinez and Rudzynsky (1997) and Grace (2001) predict a reduction in unsteady lift with increasing frequency for a thick foil relative to a foil without thickness. These trends agree with the leading edge dipole sound measurements made by Olsen and Wagner (1982) with airfoils of varying thickness. The BVI calculations are also substantiated by the difference between the measured dipole sound spectra from a NACA 0012 airfoil and the sound spectra predicted by a zero thickness theory Amiet (1976,1977)] as illustrated in Fig.…”

“…The calculated surface pressure spectrum for the mean shear flow, when combined with the results of Section 2, yield a prediction formula for the leading edge lifting dipole sound of a thick, acoustically non-compact foil cutting through a shear layer. Estimates of the measured leading edge dipole sound by Olsen and Wagner (1982) are made for incident sources with and without the mean shear term. These estimates establish the frequency below which the mean shear source dominates the source without mean shear.…”

“…The dipole sound measurements made by Olsen and Wagner (1982) with airfoils in the shear layer of a 10 cm diameter round jet will be predicted using estimates of the incident 31 sources with and without mean shear from equations [Eq. (4.27) Olsen and Wagner (1982) was able to predict the leading edge noise for the thin airfoil without taking into account the mean shear source.…”

Reduced Dimension Modeling of Leading Edge Turbulent Interaction Noise

“…At K = 12, there is very little noise reduction shown by the NACA 0004 case, while about 5 dB is shown by the NACA 0008 case, and about 11 dB is shown by the NACA 0012 case. Previous studies, such as those by Olsen and Wagner, 8 and Roger and Moreau, 10 have reported an apparent linear decrease in noise with increasing airfoil thickness. To explain the discrepancy between previous studies and the current work, the variation of both sound power P , and PWL, with increasing airfoil thickness t, is shown in Figure 13 at two reduced frequencies.…”

Leading Edge Surface Pressures from Airfoils in a Turbulent Flow

“…The dependence of the foil thickness on the dipole sound was determined from measurements by Amiet (1976,1977) and Olsen and Wagner (1982). These measurements demonstrated that the foil's thickness attenuates the leading edge lifting dipole soimd progressively with increasing frequency over that for the zero-thickness case modeled by Scare (1941), Numerical simulations in the spatial domain using blade vortex interaction (BVI) methods by Martinez and Rudzinski (1997) and Grace (2001) have also captured the affect of foil thickness on the unsteady lift.…”