Turbulence Closure for Static and Dynamic Stall in the Transitional Regime
Speaker: Joachim Hodara, Ph.D. candidate, The Georgia Institute of Technology
Presentation
Abstract
The aerodynamics of modern rotorcraft is highly complex and has proven to be an arduous challenge for Computational Fluid Dynamics (CFD). Flow features such as massively separated boundary layers or transition to turbulence are common in engineering applications and need to be accurately captured in order to predict the vehicle performance. The recent advances in numerical methods and turbulence modeling have resolved each of these issues independent of the other. First, state-of-the-art hybrid RANS-LES turbulence closures have shown great promise in capturing the unsteady flow details and integrated performance quantities for stalled flows. Similarly, the correlation-based transition model of Langtry and Menter has been successfully applied to a wide range of applications involving attached or mildly separated flows. However, there still lacks an unified approach that can tackle massively separated flows in the transitional flow region. In this effort, the two approaches have been combined and expended to yield a methodology capable of accurately predicting the features in these highly complex unsteady turbulent flows at a reasonable computational cost.
This new turbulence approach will be applied to the study of wings in the reverse flow regime. The flight envelope of modern helicopters has increased significantly over the last few decades, with design concepts now reaching advance ratios up to μ = 1. In these extreme conditions, the freestream velocity exceeds the rotational speed of the blades, and a large region of the retreating side of the rotor disk experiences reverse flow. For a conventional airfoil with a sharp trailing edge, the reverse flow regime is generally characterized by massive boundary layer separation and bluff body vortex shedding. This complex aerodynamic environment is perfectly suited to evaluate the new hybrid transitional approach. The current capability of advanced numerical models to predict blade performance and wakes in reverse flow will be assessed, and best practices for prediction of static and dynamically moving airfoils defined accordingly.
Biography
Joachim Hodara is a Ph.D. candidate and graduate research assistant in the Guggenheim School of Aerospace Engineering at the Georgia Institute of Technology. Before coming to Georgia Tech, he received two M.S. degrees from Cranfield University and Ecole Centrale de Lille. His honors and awards include a Best Paper Award (Aerodynamics) at the 71st AHS Forum (2015), two Vertical Flight Foundation scholarships (2013 and 2014), the Southern Regional Lichten Award (2014) and the Director’s prize for best performance in the M.S. at Cranfield University (2012). His research at Georgia Tech focuses on transition and turbulence modeling for rotorcraft applications.