Laminar to Turbulent Transition with Transport Equation on 2D and 3D Incompressible Flows
Creators: name: DE ROSA, Donato
name: CATALANO, Pietro
Publisher: name: Proceedings of the 8th European Conference for Aeronautics and Space Sciences. Madrid, Spain, 1-4 july 2019
Year: 2019
Subjects: CFD
LAMINARITY
TURBULENCE
LARGE EDDY SIMULATION
SUBSONIC

description: The prediction of boundary-layer transition region plays a key role in the simulation of aerodynamic flows in order to correctly predict lift and drag forces and, thus, the overall performance. The design of airfoils and wings is strongly affected by the accuracy in transition prediction. This requirement is further stressed for all the cases where the laminar- turbulent transition process highly influences the flow field, such as natural laminar-flow, laminar flow control, rotor helicopter and wind turbine blade design. Reynolds Averaged Navier Stokes (RANS) equations are widely used by the aeronautical industry for the sim- ulation of viscous flows, and CFD codes capabilities in simulating fully turbulent flows have been widely assessed. Several attempts to improve the reliability of numerical results were performed in order to reproduce free transitional flows. An usual way is to impose a transition point in 2D and a line in 3D environment. This technique requires a priori knowledge of the transition location from experimental data or the use of other transition prediction approaches like engineering correlations or e N method. 1, 2 Nevertheless, transition region is not computed in CFD codes and a sudden shift between laminar and turbulent region is observed. Hence, in the last decades, several methods to model the tran- sition region have been investigated. Some of these models are based on a physics-based RANS formulation and the most prominent is the Laminar Kinetic Energy proposed by Walters and Leylek. 3, 4 Recently, a new correction was also proposed by Lopez and Walters. 5 An alternative to physics-based formulation is the so-called Local-Correlation based Transition Modeling (LCTM) concept, where the different transition processes are not modeled, but a set of transport equations are formulated to combine experimental correlations via triggering functions. A widely known model is the one proposed by Langtry and Menter, 6 namely the Re model. In 2015, Menter et al. 7 proposed a new transition model, namely the model, that is based on the previous one, but only the transport equation for the intermittency is present while the momentum-thickness Reynolds number is algebraically computed using local variables. In addition to a simplified formulation for the momentum-thickness Reynolds number, this model is also Galilean invariant, unlike the previous one. This paper deals with the implementation of the model 7 coupled with the SST turbulence model, into the in-house RANS flow solver UZEN 8 and its validation for 2D and 3D flows. For bi-dimensional analyses the Eppler 387 airfoil 9 is used. Results from RANS code are compared with ex- perimental data and Large Eddy Simulation (LES) results. A low Reynolds number airfoil, namely SD 7003, is also simulated and compared with LES results. 10, 11 The 6 : 1 prolate spheroid 12 is used as three-dimensional test case, where transition process is induced by both Tollmien-Schilchting and cross-flow instabilities.