55 research outputs found
Large-Eddy Simulation: Current Capabilities, Recommended Practices, and Future Research
This paper presents the results of an activity by the Large Eddy Simulation (LES) Working Group of the AIAA Fluid Dynamics Technical Committee to (1) address the current capabilities of LES, (2) outline recommended practices and key considerations for using LES, and (3) identify future research needs to advance the capabilities and reliability of LES for analysis of turbulent flows. To address the current capabilities and future needs, a survey comprised of eleven questions was posed to LES Working Group members to assemble a broad range of perspectives on important topics related to LES. The responses to these survey questions are summarized with the intent not to be a comprehensive dictate on LES, but rather the perspective of one group on some important issues. A list of recommended practices is also provided, which does not treat all aspects of a LES, but provides guidance on some of the key areas that should be considered
Wave propagation in gaseous small-scale channel flows
The propagation and attenuation of an initial shock wave through a mm-scale channel of circular cross-section over lengths up to 2,000 diameters is examined as a model problem for the scaling of viscous effects in compressible flows. Experimental wave velocity measurements and pressure profiles are compared with existing data and theoretical predictions for shock attenuation at large scales and low pressures. Significantly more attenuation is observed than predicted based on streamtube divergence. Simulations of the experiment show that viscous effects need to be included, and the boundary layer behavior is important. A numerical model including boundary layer and channel entrance effects reproduces the wave front velocity measurements, provided a boundary layer transition model is included. A significant late-time pressure rise is observed in experiments and in the simulations
CAA boundary conditions for airfoil noise due to high-frequency gusts
AbstractThis paper proposes inflow and outflow boundary conditions for direct computation of airfoil noise under the influence of impinging gusts with a particular interest in the high frequency response. The proposed boundary conditions are based on an existing zonal sponge technique that has been used mostly to attenuate outgoing disturbances and absorb reflections from computational boundaries. A modified form of the sponge technique is presented in this paper in order to specify an incoming disturbance. The proposed boundary conditions still maintain the genuine non-reflective features that lead to accurate calculations of far-field sound intensity and directivity. It is also shown that the proposed boundary conditions enable the use of a significantly smaller domain size, and hence fewer grid cells, than used in conventional airfoil calculations, which enables the calculation of high-frequency gust-airfoil noise at a much lower computational cost. The proposed boundary conditions are validated against CAA (computational aeroacoustics) benchmark solutions after a variety of parametric tests, through which an optimal combination of the domain size, sponge thickness and a sponge coefficient is obtained for the highest efficiency. The proposed boundary conditions yield more accurate and consistent solutions particularly at the far field than the conventional ones. Further applications to high-frequency gust responses are performed to observe and demonstrate significant changes in the sound intensity and directivity varying with different frequencies and gust incidence angles
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