Comparative Studies of RANS Versus Large Eddy Simulation for Fan–Intake Interaction

Abstract

The present research applied a mixed-fidelity approach to examine the fan–intake interaction. Flow separation induced by a distortion generator (DG) is either resolved using large eddy simulation (LES) or modeled using the standard k–ω model, Spalart–Allmaras (SA) model, etc. The immersed boundary method with smeared geometry (immersed boundary method with smeared geometry (IBMSG)) is employed to represent the effect of the fan and a wide range of test cases is studied by varying the (a) height of the DG and (b) proximity of the fan to the DG. Comparisons are drawn between the LES and the Reynolds-averaged Navier–Stokes (RANS) approaches with/without the fan effect. It is found that in the “absence of fan,” the discrepancies between RANS and LES are significant within the separation and reattachment region due to the well-known limitations of the standard RANS models. “With the fan installed,” the deviation between RANS and LES decreases substantially. It becomes minimal when the fan is closest to the DG. It implies that with an installed fan, the inaccuracies of the turbulence model are mitigated by the strong flow acceleration at the casing due to the fan. More precisely, the mass flow redistribution due to the fan has a dominant primary effect on the final predictions and the effect of turbulence model becomes secondary, thereby suggesting that high fidelity eddy resolving simulations provide marginal improvements to the accuracy for the installed cases, particularly for the short intake–fan strategies with fan getting closer to intake lip.

Quasi 3D Nacelle Design to Simulate Crosswind Flows: Merits and Challenges

“…It is well known that the post-separation predictive capability of steady RANS models is questionable. Unsteady RANS or the presence of fan (see [17]) can alleviate these deficiencies to some extent. Nevertheless, we limit scope of the current study to steady RANS, since the objective of this paper is to verify if the Q3D can reproduce the flow characteristics of F3D on the intake lip using the same computational techniques.…”

The energy equation for modeling reacting flows on RANS, LES and DES approaches

“…It allows solving the whole range of spatial and temporal scales of turbulence without being necessary to implement turbulence models. But this technique, at least for now, is out of reach for all engineering applications [11,12,13,14,15,16,17,18]. The large eddies simulation (LES) technique, developed relying on the spectral filtering of the turbulent energy, is a better form of dealing with turbulence normally found in engineering applications [19,20,21].…”

Body Force Model Implementation of Transonic Rotor for Fan/Airframe Simulations

“…Body force models have been shown to replicate some mechanisms of distortion transfer, flow redistribution, and nonuniform work input into the fluid in fans, providing a two-order-of-magnitude faster response compared to URANS [31][32][33]. However, according to the specific variant considered, the qualitative and quantitative agreement can be different, making it more difficult to judge in advance their real fidelity without a complete validation.…”