Representative applications are described which illustrate the extent to which simplifications in the solutions of high-speed unsteady aeroelastic problems can be achieved through the use of certain aerodynamic techniques known collectively as "piston theory." Based on a physical model originally proposed by Hayes and Lighthill, piston theor}^ for airfoils and finite wings has been systematically developed by Landahl, utilizing expansions in powers of the thickness ratio 8 and the inverse of the flight Mach Number M. When contributions of orders 8/M and 8/M are negligible, the theory predicts a point-function relationship between the local pressure on the surface of a wing and the normal component of fluid velocity produced by the wing's motion. The computation of generalized forces in aeroelastic equations, such as the flutter determinant, is then always reduced to elementary integrations of the assumed modes of motion.

Piston Theory-A New Aerodynamic Tool for the Aeroelastician

https://www.colonius.caltech.edu/pdfs/ColoniusLele2004.pdf

Computational aeroacoustics: progress on nonlinear problems of sound generation

Shock associated noise of supersonic jets from convergent-divergent nozzles

Origins of spectral methods, especially their relation to the Method of Weighted Residuals, are surveyed Basic Fourier, Chebyshev, and Legendre spectral concepts are reviewed, and demonstrated through application to simple model problems Both collocation and tau methods are considered These techniques are then applied to a number of difficult, nonlinear problems of hyperbolic, parabolic, elliptic, and mixed type Fluid dynamical applications are emphasized

/pdf/spectral-methods-for-partial-differential-equations-21v4at2p7x.pdf

Spectral Methods for Partial Differential Equations

Select methods are reviewed that have been used by the scramjet community to enhance mixing of fuel with oxidizer to achieve high combustion efe ciency with reduced length combustors. The review also includes research on enhanced supersonic free shear layer mixing from the jet noise reduction community. This latter community has considered concepts involving acoustic excitation or passive excitation of shear layer instabilities to minimize noise production. Several of these concepts are amendable to active control for system optimization.

Historical Survey on Enhanced Mixing in Scramjet Engines

Interaction of convected field of turbulence with shock wave is analyzed to yield modified turbulence, entropy spottiness, and noise generated downstream of the shock Analysis is generalization of single-spectrum-wave treatment of NACA-TN-2864 Formulas for spectra and correlations are obtained Numerical calculations yield curves of rms velocity components, temperature, pressure, and noise in db against Mach number for m = 1 to infinity; both isotropic and strongly axisymmetric (lateral/longitudinal = 36/1) initial turbulence are treated In either case, turbulence of 01 percent longitudinal component generates about 120 dbs of noise

/pdf/shock-turbulence-interaction-and-the-generation-of-noise-1m3j672joe.pdf

H S Ribner

Papers

Shock-turbulence interaction and the generation of noise