RANS simulations of a simplified tractor/trailer geometry.

Steady-state Reynolds-Averaged Navier-Stokes (RANS) simulations are presented for the three-dimensional flow over a simplified tractor-trailer geometry at zero degrees yaw angle. The simulations are conducted using the SACCARA multi-block, structured CFD code. Two turbulence closure models are employed: the one-equation Spalart-Allmaras model and the two-equation k-ω model of Menter. The discretization error is estimated by employing two grid levels: a fine mesh of approximately 20 million grid points and a coarse mesh of approximately 2.5 million grid points. Simulation results are compared to the experimental data obtained at the NASA-Ames 7×10 ft wind tunnel. Quantities compared include: surface pressures on the tractor/trailer, vehicle drag, and time-averaged velocities in the base region behind the trailer. The results indicate that both turbulence models are able to accurately capture the surface pressure on the vehicle, with the exception of the base region. The Menter k-ω model does a reasonable job of matching the experimental data for base pressure and velocities in the near wake, and thus gives an accurate prediction of the drag. The Spalart-Allmaras model significantly underpredicted the base pressure, thereby overpredicting the vehicle drag.

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