Validation of the $$\gamma \text{-Re }_{\theta }$$ Transition Model for Airfoils Operating in the Very Low Reynolds Number Regime

Abstract

Micro Aerial Vehicles (MAVs) are state of the art in the aerospace industry and are involved in many operations. The reduced dimensions of these vehicles generate very low Reynolds number conditions in which separation-induced transition typically occurs. The extremely large computational cost of scale resolving simulations, which are capable of capturing laminar to turbulent transition, is prohibitive for most engineering and design applications. Therefore, it becomes very interesting to couple transition models with conventional Reynolds Averaged Navier–Stokes (RANS) simulations to allow the prediction of transition to turbulence at a reduced computational cost. This paper performs an investigation of the application of the $$\gamma \text{-Re }_{\theta }$$ γ -Re θ transition model analysing different empirical correlations available in literature and studying the influence of the relevant model parameters using the commercial Computational Fluid Dynamics (CFD) code STAR-CCM+. The flow around the Eppler 387, Selig/Donovan 7003 and Ishii airfoils has been studied for different Reynolds numbers and angles of attack comparing the drag and lift forces and separation bubble characteristics with experimental and numerical results reported in literature.

Assessment of a RANS Transition Model with Flapping Foils at Moderate Reynolds Numbers

“…For instance, when the Reynolds number is of the order of 10 4 or 10 5 , employing a transition model enables capture of phenomena such as formation of a laminar separation bubble over an airfoil and more accurate prediction of the onset of the stall. Despite the availability of results involving transition models applied to airfoils at moderate Reynolds number, even recently [20], the authors are not aware of studies that specifically consider the oscillating motion of airfoils using RANS and a local transition algebraic model. This is the main subject of this work.…”

Large Eddy simulations and Reynolds-averaged Navier-Stokes simulations of separation-induced transition using an unstructured finite volume solver

“…When comparing our RANS and LES approaches, we observe a noticeable shift of the separation bubble towards the trailing edge. This discrepancy arises because the RANS model follows the recalibration performed in reference [9], which utilized the Galbraith ILES results [1] as a reference. Nevertheless, the overall agreement is satisfactory.…”

“…The time-step was set to 0.01 convective turnovers. Further details regarding the numerical setup of the RANS simulations and the implementation of the 𝛾𝛾 − 𝑅𝑅𝑒𝑒 𝜃𝜃 transition model can be found in [9]. For LES, the SD7003 geometry was extruded in the spanwise direction for 0.1 chords, which has been determined by [1] as sufficient for computing flow statistics at low and moderate angles of attack.…”

“…De Santis et al [7] recently introduced a modification of the γ transition model [8] to enhance turbulent kinetic energy production within separation bubbles. Carreño et al [9] also attempted to increase turbulent kinetic energy production in separation bubbles by tuning the 𝑠𝑠 1 parameter in the 𝛾𝛾 − 𝑅𝑅𝑒𝑒 𝜃𝜃 transition model [10].…”

Parametrization Effects of the Non-Linear Unsteady Vortex Method with Vortex Particle Method for Small Rotor Aerodynamics

“…Refinement is used near the leading and trailing edges and in the airfoil wake, leading to a total cell count of 182,720. The StarCCM+ simulations are conducted with the full turbulent K-Omega-SST (KwSST) and with the KwSST with transitional Gamma-R-Theta [47] (GRT). Then, the in-house 2D structured finite volume RANS solver (NSCODE [43]) is used with the full turbulent Spalart-Allmaras (SA), as done in the previous work [5].…”