Abstract
Regulations on global greenhouse gas emission are driving the development of more energy-efficient passenger vehicles. One of the key factors influencing energy consumption is the aerodynamic drag where a large portion of the drag is associated with the base wake. Environmental conditions such as wind can increase the drag associated with the separated base flow. This paper investigates an optimised yaw-insensitive base cavity on a square-back vehicle in steady crosswind. The test object is a simplified model scale bluff body, the Windsor geometry, with wheels. The model is tested experimentally with a straight cavity and a tapered cavity. The taper angles have been optimised numerically to improve the robustness to side wind in relation to drag. Base pressures and tomographic Particle Image Velocimetry of the full wake were measured in the wind tunnel. The results indicate that a cavity decreases the crossflow within the wake, increasing base pressure, therefore lowering drag. The additional optimised cavity tapering further reduces crossflow and results in a smaller wake with less losses. The overall wake unsteadiness is reduced by the cavity by minimising mixing in the shear layers as well as dampening wake motion. However, the coherent wake motions, indicative of a balanced wake, are increased by the investigated cavities.Graphical abstract
Highlights
There is a demand for more energy-efficient vehicles as greenhouse gas emissions and air quality regulations have become more strict
The aerodynamic drag accounts for more than a quarter of the traction energy required based on the WLTP test cycle (WLTP is the World Light Vehicle Test protocol that is widely used in the certification of vehicle emissions) Pavlovic et al (2016)
All the flow fields and pressure measurements presented are generated from the wind tunnel experiments
Summary
There is a demand for more energy-efficient vehicles as greenhouse gas emissions and air quality regulations have become more strict. One of the key performance indicators of energy efficiency is the aerodynamic drag. The aerodynamic drag accounts for more than a quarter of the traction energy required based on the WLTP test cycle (WLTP is the World Light Vehicle Test protocol that is widely used in the certification of vehicle emissions) Pavlovic et al (2016). Road vehicle flow fields are characterised by large unsteady wakes, and the drag is dominated by pressure drag that accounts for approximately for approximately 90% of the total drag Schuetz (2015). Howell et al (2018) showed that vehicles with similar drag coefficients at 0◦ yaw can have large differences in drag in a crosswind The improvements close to the front wheel deflectors were maintained; the downstream improvements were reduced under turbulent conditions. Howell et al (2018) showed that vehicles with similar drag coefficients at 0◦ yaw can have large differences in drag in a crosswind
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