Comparative Study of Transition Models for High-Angle-of-Attack Behavior

Abstract

This paper considers transition modeling for the flow over small unmanned aerial vehicles with a span of around 1 m. Such flows are characterized by very low values of turbulent intensity and the main cause for transition corresponds to flow separation. Four different turbulence models for low Reynolds number flow are compared with the experimental data for a NACA 0018 airfoil over a range of 2D as well as 3D conditions. The turbulence models under consideration are Menter's k − ω SST model with Wilcox's low-Re modification, Menter & Langtry's (k − ω SST) γ − Re θ model along with its simplified version in the form of the (k − ω SST) γ model, and Walters & Coklja's k − k l − ω model. The NACA 0018 profile is rotated in a flow with a chord-based Reynolds number of 3×10 5 at three different rotational speeds between an angle of attack (AoA) of 0 o and 25 o . Using a curve fitting methodology, an estimate of the results at an infinitesimally slow rotation can be made. Both clockwise and counterclockwise rotations are considered to allow an assessment of the model for predicting steady hysteresis. Furthermore, 3D computations for an infinite wing are performed to examine the appearance of coherent structures at high AoA, namely, stall cells or low frequency fluctuations.

Laminar Separation Bubble and Flow Topology of NACA 0015 at Low Reynolds Number

“…Therefore, results on the suction side suggest that with increasing Reynolds number and angle of attack, the laminar separation bubble propagates towards the leading edge causing early transition and reattachment at some instances. However, with an increasing angle of attack, the separation point moves downstream on the pressure side [38]. Majority of the cases, bubbles are produced at both sides of the airfoil for Re = 1.7 × 10 5 except α = 3 o (Figure 7(h)).…”

“…This model is not depending on nonlocal terms and the intermittency is modified to allow better prediction of separation-induced transition [26,32,36]. Additionally, the model predicts the formation and structure of the separated bubble well [37][38][39]. Above all, the model is mostly used for external flow measurements at relatively high Reynolds number (Re ≈ 10 6 ) and finite low Reynolds number [28].…”

Multi-objective optimization of a wing fence on an unmanned aerial vehicle using surrogate-derived gradients

“…The latter assures that the model captures strong variations of the turbulent intensity, that may occur due to turbulence decay, the influence of the free-stream and the pressure gradient [22]. This model was chosen over other transitional models based on a comperative study with experimental data for high angle of attack behavior [36].…”

“…In the last couple of decades, a number of turbulence models have been developed that attempt to model the transition phenomena that are attributed to low Reynolds number flow. Here Menter et al's γ − Re θ model [22] is used based on a comparative study of transitional turbulence models [36]. It results in deviations of CL and CD up to 10% for the investigated conditions near the stall angle.…”

Prediction of Static Aerodynamic Hysteresis on a Thin Airfoil Using OpenFOAM

“…The prediction was close to the experimental results for = 0.3 × 10 6 presented in [5,6,12], but was not satisfactory for = 0.7 × 10 6 . In a recent study [13], a comparative analysis of transition turbulence models was carried out with the objective of capturing aerodynamic static hysteresis. It was shown that the and -turbulence models predict the laminar bubble on the top branch rather well at = 0.3 × 10 6 , giving a small overshoot in max , but they are completely unable to predict the lower branch of the static aerodynamic hysteresis with fully developed flow separation.…”