What Was Learned in Predicting Slender Airframe Aerodynamics with the F-16XL Aircraft

Abstract

The CAWAPI-2 coordinated project has been underway to improve CFD predictions of slender airframe aerodynamics. The work is focused on two flow conditions and leverages a unique flight data set obtained with the F-16XL aircraft for comparison and verification. These conditions, a low-speed high angle-of-attack case and a transonic low angle-of-attack case, were selected from a prior prediction campaign wherein the CFD failed to provide acceptable results. In re-visiting these two cases, approaches for improved results include better, denser grids using more grid adaptation to local flow features as well as unsteady higher-fidelity physical modeling like hybrid RANS/URANS-LES methods. The work embodies predictions from multiple numerical formulations that are contributed from multiple organizations where some authors investigate other possible factors that could explain the discrepancies in agreement, e.g. e ects due to deflected control surfaces during the flight tests, as well as static aeroelastic deflection of the outer wing. This paper presents the synthesis of all the results and findings and draws some conclusions that lead to an improved understanding of the underlying flow physics, and finally making the connections between the physics and aircraft features.

F-16XL Simulations at Flight Conditions Using Hybrid Near-Body/Offbody Computational Fluid Dynamics

“…In a review paper by Rizzi and Luckring [5], it was noted that steady Reynolds-averaged Navier-Stokes (RANS) modeling was sufficient to compute solutions to many CAWAP flight conditions; but, flight condition 25 (FC25), in particular, required fully timeaccurate methods including unsteady hybrid turbulence treatment. For this reason, a follow-on to CAWAPI called CAWAPI-2 was initiated to focus an international group of researchers on computing unsteady solutions to FC25 using hybrid unsteady RANS/large-eddy simulation (LES) methods.…”