Emin Issakhanian

An Aerodynamic Investigation of an Isolated Stationary Formula 1 Wheel Assembly

The flowfield around a 60% scale rotating Formula 1 tire in contact with the ground in a closed wind tunnel at a Reynolds number of 500,000 was examined computationally and experimentally. The goal of this study was to assess the accuracy of unsteady Reynolds-averaged Navier–Stokes (URANS) equations and confirm the existence of large scale vortical and flow recirculating features. A replica deformable F1 tire model that includes four tire treads and all brake components was used to determine the sensitivity of the wake to cross flow within the tire hub as well as the flow blockage caused by the brake assembly. Several turbulence closures were employed and the one that matched closest to the experimental PIV data was the Reynolds stress model. The variability between the six turbulence closures is shown by comparing velocity profiles, pressure distributions, and vortex eccentricity. The sensitivity of the wake to four different hub geometries, contact patch boundary conditions, multiple reference frame (MRF) rotor and spoke treatment, and time step size are also discussed.

An Experimental Study of the Flow Around a Formula One Racing Car Tire

The wake of the front tires affects the airflow over the remainder of a fenderless race car. The tires can also be responsible for up to 40% of the vehicle’s drag. Prior experiments have used compromised models with solid, symmetric hubs and nondeformable tires. The present experiment acquires particle image velocimetry measurements around a 60% scale model of a deformable pneumatic tire fitted to a spoked Formula 1 wheel with complete brake geometry and supplementary brake cooling ducts. The results show reversed flow regions in the tire wake, asymmetric longitudinal vortex structures behind the tire, and a tire wake profile that is unlike previous experimental results and postulations. The flow through the hub of the wheel causes a shift of the wake inboard (toward the car) so that the outboard side of the wake does not extend past the outline of the tire.

Computational and experimental investigation of the flow structure and vortex dynamics in the wake of a Formula 1 tire

The flow field around a 60% scale stationary Formula 1 tire in contact with the ground in a closed wind tunnel is examined experimentally in order to validate the accuracy of different turbulence modeling techniques. The results of steady RANS and Large Eddy Simulation (LES) are compared with PIV data performed within the same project. The far wake structure behind the wheel is dominated by two strong counter-rotating vortices. The locations of the vortex cores, extracted from the LES and PIV data as well as computed using different RANS models, show that the LES predictions are closet to the PIV vortex cores. All turbulence models are able to accurately predict the region of strong downward velociy between the vortex cores in the centerplane of the tire, but discrepancies arise when velocity profiles are compared close to the inboard and outboard edges of the tire, due to the sensitivity of the solution to the tire shoulder modeling. In the near wake region directly behind the contact patch of the tire, contour plots of inplane-velocity are compared for all three datasets. The LES simulation again matches well with the PIV data.

Film Cooling Effectiveness Improvements Using a Non-Diffusing Oval Hole

The need for improvements in film cooling effectiveness over traditional cylindrical film cooling holes has led to varied shaped hole and sister hole designs of increasing complexity. This paper presents a simpler shaped-hole design which shows improved film cooling effectiveness over both cylindrical holes and diffusing fan-shaped holes without the geometric complexity of the latter. Magnetic resonance imaging measurement techniques are used to reveal the coupled 3D velocity and coolant mixing from film cooling holes which are of a constant oval cross-section as opposed to round. The oval shaped hole yielded an area-averaged adiabatic effectiveness twice that of the diffusing fan-shaped hole tested. Three component mean velocity measurements within the channel and cooling hole showed the flow features and vorticity fields which explain the improved performance of the oval shaped hole. As compared to the round hole, the oval hole leads to a more complex vorticity field which reduces the strength of the main counter-rotating vortex pair. The counter-rotating vortex pair acts to lift the coolant away from the turbine blade surface and thus strongly reduces the film cooling effectiveness. The weaker vortices allow coolant to stay closer to the blade surface and to remain relatively unmixed with the main flow over a longer distance. Thus, the oval-shaped film cooling hole provides a simpler solution for improving film cooling effectiveness beyond circular hole and diffusing hole designs.Copyright

Magnetic Resonance Imaging Techniques for Measuring Film Cooling Flow Velocity and Effectiveness

Film cooling of gas turbine engine components directly influences the efficiency and lifetime of the engine. Prediction of the film cooling surface effectiveness remains a problem area for engine designers. Magnetic Resonance Imaging (MRI) measurements of the surface film cooling effectiveness can be made using the analogy between temperature and passive scalar concentration in which the concentration of scalar marked cooling fluid is measured as it mixes with the main flow. The present work specifically addresses refinements to MR imaging techniques needed to accurately measure the concentration of a scalar contaminant at a flow-bounding surface. Anecdotal data are presented from experiments in which a single film jet exits into the boundary layer on one wall of a square channel. Data are presented for hole angles α = 30° and 60° and blowing ratios BR = 0.5 and 1.0. The Reynolds number of the main channel based on hydraulic diameter and bulk velocity is 400,000 and the jet Reynolds number at BR = 1.0 is 5300.Copyright

Magnetic Resonance Imaging Studies of Flow and Mixing for Single-Hole Film Cooling

Magnetic resonance imaging (MRI) measurement techniques are used to reveal the coupled 3D velocity and coolant concentration fields for a single film cooling hole with L/D of 4, ejection angle of 60°, and blowing ratios of 0.5 and 1. The jet exits into a boundary layer with momentum thickness of 0.1D. Magnetic resonance velocimetry (MRV) measures 3 component mean velocity everywhere within the channel, cooling hole, and feed plenum. Magnetic resonance concentration (MRC) provides the coolant concentration distribution which is directly analogous to film cooling effectiveness. The coupled velocity and concentration show that high velocity ratios lead to a detached jet which lowers effectiveness. Vorticity from the feed hole creates a streamwise oriented counter rotating vortex pair which lifts the coolant stream from the surface and sweeps in main channel flow inducing a kidney-shape to the coolant jet cross-section. Without the need for optical access, MRV allows study of the flow inside the feed hole including the entrance separation and secondary flows. Cross-stream feeding of the cooling hole shows added spanwise asymmetry at the hole entrance, but this asymmetry is significantly reduced moving up the hole.© 2011 ASME