Investigation of Low-Profile Vortex Generators via Experimental Methods

Abstract

A novel low-profile vortex generator has recently demonstrated fuel savings of 1% on commercial aircraft. It has been termed a Conformal Vortex Generator (CVG) and consists of a backward facing step where the chord position of the step periodically varies in the spanwise direction. The fluid mechanism response for the observed fuel savings remains unclear. The current work aims to understand the behavior at subsonic conditions via two sets of experiments. The first experiment used particle-image-velocimetry in a water tunnel to study the flow over a CVG on a flat plate. Measurements were acquired immediately downstream of the peak, valley, and mid-locations as downstream distance based Reynolds numbers between 60,000 and 900,000. This study showed that with a laminar inlet the flow downstream of the peak transitions to turbulent flow while downstream of the valley it remains laminar, which results in significant spanwise variation in the velocity distribution. The second experiment used Pitot-static probes (single and multi-hole) to acquire wake surveys in a wind tunnel downstream of an LA203A airfoil with either a CVG, backward facing step, or a clean wing configuration. Multiple CVG configurations were studied at a chord based Reynolds number of 300,000 and the angle of attack varied from 0 to 10 degrees. The CVGs generated strong coherent structures that persisted at least five chord lengths in the airfoil wake. The general trend was that the smaller the CVG the weaker the coherent structures. At higher angles of attack, the coefficient of drag increased the further upstream the CVG was located. In general, CVG outperformed a backward facing step but not the clean wing configuration.