Scale resolving simulation of wing lower surface buffet effects induced by the installation of a UHBR nacelle

Abstract

The integration of large engine nacelles below the wing of an aircraft is accompanied by a variety of aerodynamic effects such as unsteady shock buffet occurring on the lower surface of the wing. In this study these effects are investigated by applying a hybrid RANS-LES method on a commercial transport aircraft configuration at high subsonic Mach number and low angle of attack. A local region on the wing lower surface confined by the pylon and the fuselage is thereby simulated using an IDDES approach allowing a detailed assessment of the interaction of the transonic shock with the turbulent boundary layer while the remaining computational domain is simulated using a RANS method with a Reynolds-stress turbulence model. To allow a smooth transition between the RANS and the LES region a synthetic turbulence generator is located upstream of the shock which translates the modeled turbulence of the RANS model coming from upstream into local temporal and spatial resolved fluctuations. Here we show that the IDDES approach accurately computes the wing lower surface buffet effects. Comparisons with wind tunnel experiments show excellent agreement in terms of local pressure distributions and pressure fluctuations on the wing lower surface around the shock and a significant improvement of the simulation accuracy compared to conventional approaches based on pure RANS modeling. Spectral analysis of the unsteady shock motion shows a good agreement between the IDDES and experimental data supporting previous findings that the lower wing buffet phenomenon is associated with Strouhal numbers in the range of 0.2 to 0.4. This Strouhal number range matches with studies on classical buffet on the wing suction side indicating that a similar mechanism is at work.