Vortical flow prediction for the design of a wind tunnel experiment with a pitching lambda wing

Abstract

The IWEX wind tunnel model (Instationäres Wirbelexperiment, German for: Unsteady Vortex Experiment) was developed to study vortical flow at static and oscillating angles of attack. Numerical computations were performed beforehand to study important aerodynamic aspects. The focus of this paper is on those results that were affecting the design of the model. The experimental concept of a new test rig, wind tunnel walls and the new half wing model is briefly described. The lambda wing has a purely round leading edge with a constant nose radius to chord ratio of 0.5 %. The flow characteristics of the main vortex, generated at the nose of the main wing, and the smaller tip vortex are specified. The inboard motion of the main vortex with increasing angle of attack and the consequences for the load distribution are described. The free stream Mach number range of the test envelope is from 0.3 to 0.7. Therefore, transonic effects, especially shock-vortex interactions triggering vortex development, had to be analyzed for a safe design of the model. A peniche was designed to minimize the differences of the flow character compared to reference results of the model without wind tunnel walls. The effects of corner separation and displacement are specified at different stages of the iterative process. Finally, basic results for a pitching motion are discussed, based on global and distributed coefficients.

Development of a wind tunnel experiment for vortex dominated flow at a pitching Lambda wing

“…13). Beyond an a of 16°at This effect is very sensitive and strongly affected by the position of the shock and the separation of the vortex from the surface [8]. Depending, e.g., on the turbulence model, a shock position can easily vary by some percent of the chord length already for flow without vortices at a lower a.…”

“…The effects on the flow originate from a horseshoe vortex at the leading edge and a corner separation at the trailing edge near the junction of the wall and the wing [7]. Without a peniche, this results mainly in a displacement of the main vortex in the direction of the tip which can lead to a change of the vortex topology by a merging of the tip and the main vortex [8].…”

“…Subsonic and transonic cases had to be selected because they differ in their behavior regarding the vortex development and therefore their load distribution. Initially, Mach numbers were selected that clearly show either the one or the other character [8] to study this effect (Fig. 4), even though Mach 0.8 is not part of the planned measurement envelope.…”