PREDICTION OF ROTOR HIGH-SPEED IMPULSIVE NOISE WITH A COMBINED CFD–KIRCHOFF METHOD
✍ Scribed by S. Lee; J. Kim; Y.H. Yu; M.P. Isom
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 222 KB
- Volume
- 207
- Category
- Article
- ISSN
- 0022-460X
No coin nor oath required. For personal study only.
✦ Synopsis
A combined Computational Fluid Dynamics(CFD)-Kirchhoff method is presented for predicting high-speed impulsive noise generated by a rotor in hover. Two types of Kirchhoff integral formulas are used: one of them is a classical linear Kirchhoff formulation and the other a non-linear Kirchhoff formulation. An Euler finite-difference solver is executed first, from which a flow field is obtained to be used as an input to the Kirchhoff formulation to predict the acoustic far-field. The calculations are performed at Mach numbers of 0•90 and 0•95 to investigate the effectiveness of the linear and non-linear Kirchhoff formulas for delocalized flow. During these calculations, the retarded time equation is also carefully examined, in particular, for the cases where a control surface is located outside the sonic cylinder, for which multiple roots are obtained. Predicted results of acoustic far-field with the linear Kirchhoff formulation agree well with the experimental data when the control surface is at a particular location (Rcs /R = 1•46), but the correlation weakens as it moves away from this specific location of the control surface due to the delocalized non-linear aerodynamic flow field. Calculations based on the non-linear Kirchhoff equation using the sonic cylinders as the control surfaces show reasonable agreements with the experimental data in the negative amplitudes for both tip Mach numbers of 0•90 and 0•95, except for some computational integration problems over a shock. It can be concluded that a non-linear formulation is necessary if the control surface is close to the blade and the flow is delocalized.