Modeling laminar-to-turbulent transition on three dimensional wings

The location and length of the transition region as fluid progresses from laminar-to-turbulent flow is critical to accurately simulating fluid flow with wall boundaries. Despite its importance, transition models are rarely... [ view full abstract ]

The location and length of the transition region as fluid progresses from
laminar-to-turbulent flow is critical to accurately simulating fluid flow with
wall boundaries. Despite its importance, transition models are rarely included in engineering simulations because of the complexity regarding all
possible triggering processes and the difficulty in formulating a modern CFD
compatible approach that works with unstructured and parallel environments.
The aim of this research was to use a novel method called the Gamma-Rtheta Transition model to demonstrate the ability to model complex transition
with non-trivial geometry. The Gamma-Rtheta Transition model is a two transport-equation model that uses only local variables to solve the intermittency and transition onset criterion. The solution modifies the production of turbulent kinetic energy in the k-w SST turbulence model to predict laminar, transitional, or turbulent regions in the Reynolds-Averaged Navier-Stokes equations. The proposed method was applied to a NLF(1)-0416, NACA0012 and the DLR F-5 wing and compared with experimental data.
For the NLF(1)-0416 testcase, a range of angles of attack were simulated
to compute the transition location as well as the drag polar. The results
were compared against experimental data from literature and against an
existing two dimensional version of the code. Both results compare well with
experimental data as can be seen in Figure 1. The point of transition was
plotted in the left side of Figure 1 and shows a good correlation at low angles
of attack though larger discrepancies are seen at larger angles of attack. The
drag polar, the right hand plot of Figure 1, shows the transition model is
fairly accurate at predicting the overall drag.

The NACA0012 was simulated as well to verify this approach would work
on various airfoils. There was less experimental data than the NLF(1)-0416
but the transition model performs well at low angles of attack as seen in the
right side of Figure 2. As seen on the left of Figure 2, the Gamma-Rtheta Transition model still accurately predicts the coefficient of drag.

A finite span, three dimensional wing was simulated to validate the effectiveness of the Gamma-Rtheta Transition model on aircraft geometry. The geometry simulated was a DLR F-5 wing which has a symmetric airfoil section, a 20 degree sweep and the wing root blended into the side wall. The Transition
Momentum Thickness Reynolds Number is shown in Figure 3 which shows
the laminar and turbulent regions. Figure 3 only shows preliminary data
as the grid is too coarse to properly model the transitional effects due to a
shock.
The Gamma-Rtheta Transition model successfully predicted transition locations
for various angles of attack for the NLF(1)-0416 and NACA0012. An aircraft
wing(DLR F-5) was simulated and demonstrates the ability for the model to
handle aircraft complex geometry with various transitional mechanisms. The
Gamma-Rtheta Transition model fits inside the framework of large multi-processor codes and holds promise to be able to simulate the location of transition on complex geometry.