58963 - Numerical Simulation on Vortex Shedding From Airfoils of a Swirl Distortion Generator 

The need for more efficient and environmentally sustainable aircraft has been a rapidly increasing topic for research and development over the last few decades. Industry and NASA’s Glenn Research Center have been extensively testing Boundary Layer Ingestion (BLI) principles on propulsion systems. BLI has statistically shown to increase aircraft fuel efficiency by reducing overall drag and increasing thrust generation by reenergizing the aircraft wake. The StreamVane™ system, developed by Virginia Tech, is a secondary flow distortion generator that can reproduce the boundary layer flow of an aircraft or duct. These devices are constructed using complex vane packs that are additive manufactured by a strong thermoplastic resin. In turn, this provides time and cost efficient ground testing methods to evaluate BLI effects on turbomachinery components within a jet engine. 

Similar to inlet guide vanes (IGVs), the vanes within a StreamVane are designed to guide the flow into a specific profile using airfoil shapes. However, due to 3D printing limitations, the trailing edges (TEs) of these airfoils must be trimmed to create a flat surface behind the vanes. As a result, the vanes contain blunt, rectangular TEs which force the flow to separate at the pressure and suction sides of the TE. It is widely known throughout literature that this flow separation is a highly unsteady phenomenon leading to the shedding of vortices (von Karman vortex street). If these vortices shed at a frequency (shedding frequency) equal to the natural frequency of the structure, induced vibrations, deformations, and even failure can occur. Therefore, since they are placed upstream of jet engines and fan rigs, it is important to understand and characterize the vortex shedding from the vanes of StreamVane systems.

The goal of this paper is to use computational fluid dynamics (CFD) to predict the shedding frequency and coherent vortical wake structures from an airfoil profile utilized in StreamVane design. This overall goal will be accomplished in two tasks. First, a commercial 2D URANS solver will be used to model the fluid dynamics of a linear cascade experiment done by the von Karman Institute. The CFD predictions will be compared to the experimental data including shedding frequency, wake structure, Mach number distribution, and pressure and temperature distributions to validate the CFD methodology (grid size, time step, URANS, etc.). Secondly, once validated, the same methodology will be applied to airfoils within StreamVanes containing different parameters such as turning angle and TE thickness. The shedding frequency and wake structure will be calculated and plotted for each parameter through a series of unsteady simulations. As a result, more insight will be given on the correlation between certain StreamVane characteristics and the shedding frequency. Not only will these results be beneficial for StreamVane design, but also for turbomachinery components such as IGVs and turbine blades. This work is to be expanded on in the future to include 3D CFD modeling on vortex shedding from StreamVanes as well as experimental validation.