Prediction of Low Mach Number Turbulent Flow Noise Using the Splitting Method

Flow field of low Mach number (e.g. M <0.3) is usually simulated by the incompressible flow scheme due to the severe limitation of time-increment in the compressible flow scheme. In this work, we propose a modification to the usual incompressible scheme, based on the elliptic equation for pressure, to improve the accuracy for turbulent flows considering weak compressibility. Two examples will be shown to validate our method. (1) LES (Large-Eddy Simulation) was conducted for turbulent flow around NACA0012 airfoil. Particular attention was focused on the influence of compressibility, despite the low Mach number range. In addition, new subgrid scale model of one-equation type using dynamic procedure was compared with traditional Smagorinsky model. Our method successfully reproduced the separation bubble near the leading edge, resulted in the improvement in the intensity of pressure fluctuation. (2) DNS (Direct Numerical Simulation) of turbulent flow in a plane channel is carried out, taking wall temperature difference into account. As a result of the density fluctuation in near-wall eddies, asymmetric profiles are observed in turbulence statistics. By the 4-quadrant analysis of turbulent shear stress, it is found that the ejection events in the vicinity of the walls are particularly affected by the density variation.

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A Splitting Method for Aeroacoustic Noise Prediction of Low Mach Number Viscous Flows

International Journal of Aeroacoustics ◽

10.1260/1475472053730057 ◽

2005 ◽

Vol 4 (1-2) ◽

pp. 21-36 ◽

Cited By ~ 7

Author(s):

Young J. Moon ◽

J. H. Seo

Keyword(s):

Reynolds Number ◽

Mach Number ◽

Computational Efficiency ◽

Plate Thickness ◽

Splitting Method ◽

Viscous Flows ◽

Noise Prediction ◽

Acoustic Analogy ◽

Low Mach Number ◽

Aeroacoustic Noise

A set of perturbed compressible equations(PCE), based on a hydrodynamic/acoustic splitting method, is proposed for aeroacoustic noise prediction of low Mach number viscous flows. The present formulation corrects the deficiency of previous splitting methods that have no control over the coupling effects between the incompressible vorticity and the perturbed velocities. The validation test shows that the present PCE solution is in excellent agreement with those of direct acoustic numerical simulation(DaNS) and Curle's acoustic analogy for a laminar dipole tone from a 2D circular cylinder at Reynolds number based on the cylinder diameter, ReD=200 and free stream Mach number, M∞ = 0.3. Computational efficiency and accuracy requirements for PCE are also investigated for a vortex scattering noise from the trailing-edge of a thin plate at Reynolds number based on the plate thickness, Reh= 2000 and M∞ = 0.3. The test results indicate that the computational efficiency can be achieved with an acoustic grid at lower resolution, as long as the projection quality of the total derivative of the incompressible pressure, DP/Dt field is retained.

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