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Journal Article

Development of a Wind Tunnel Test Section for Evaluation of Heavy Vehicle Aerodynamic Drag at a scale of 1:3

Full scale heavy vehicle aerodynamic testing requires a very large wind tunnel test section, with few wind tunnels having this capacity worldwide. Small scale testing often requires a loss of model detail as well as introducing Reynolds Number and compressibility effects. A ¾ open jet wind tunnel set-up has been developed at Monash University Wind Tunnel that enables testing of 1:3 scale truck-trailer models, of full-scale length up to 18 metres to be tested. The measured drag on longer vehicles is more strongly affected by horizontal buoyancy and long models create additional blockage when yawed. In addition the length of the model means that special care must be taken to ensure that shear layers emanating from the nozzle at the start of the test section are sufficiently separated from the shear layers and wake at the base of the truck.
Journal Article

Contribution of Add-On Components to the Aerodynamic Drag of a Cab-Over Truck-Trailer Combination Vehicle

Results from a wind tunnel testing program of a cab-over truck-trailer combination vehicle are presented. The model is scaled at 1:3, and represents an accurate replica of currently available trucks and trailers in Australia. Cooling intakes have not been modelled. Reynolds number independence is established to the maximum obtainable in the wind tunnel test configuration adopted equating to a full-scale forward speed of 57 km/h. The wind tunnel is a ¾ open jet facility with a nozzle area of 10.9m2. The vehicle is mounted on a turntable to a 6 component force balance. A range of vehicle add-on devices are investigated, including boat-tails, side skirts, cab extenders, air-dams and roof fairings. Drag measurements are presented over a yaw angle range of 10 degrees.
Technical Paper

Experimental Assessment of CFD Predictions of Fascia Performance

A numerical and experimental investigation was undertaken to assess the accuracy and sensitivity of a commercial CFD code when predicting the effect of changes to a car fascia on radiator airflow. The Fluent CFD software program was used to model the external and underhood airflow for the front half of a car allowing the mass flow rate of air through the radiator to be calculated. These CFD predictions were compared with experimental measurements of radiator Specific Dissipation (SD) made after CFD predictions were completed. Twenty-two cases were run with five different fascias possessing air inlets that varied in size and shape. The experimental and numerical results obtained showed a 98.4% correlation coefficient with standard deviation of 2.1% on the difference between the techniques and a prediction interval of ±4.2%. Fourteen of the twenty-two cases were ranked correctly giving a Spearman Rank Coefficient of 0.992.
Technical Paper

Time Averaged and Unsteady Near-Wake Analysis of Cars

From an experimental investigation of a notchback car near-wake, a new topological structure for the wake is proposed. Although experiments were only conducted on notchback vehicles, the topology can be related to other car shapes. The unsteady behavior of the near-wake was investigated. The near-wake frequencies, which can affect ride and steering comfort, were found to be 0.11U∞/xR and 0.42U∞/xR (xR - reattachment length). The lower frequency appears to be a result of large scale vortex shedding (‘hairpin’ vortex) behind the backlight/rear-window. The higher frequency can be attributed to the shear-layer vortices.