Coupling road vehicle aerodynamics and dynamics in simulation

A fully coupled system in which a vehicle s aerodynamic and handling responses can be simulated has been designed and evaluated using a severe crosswind test. Simulations of this type provide vehicle manufacturers with a useful alternative to on road tests, which are usually performed at a late stage in the development process with a proto- type vehicle. The proposed simulations could be performed much earlier and help to identify and resolve any aerodynamic sensitivities and safety concerns before significant resources are place in the design. It was shown that for the simulation of an artificial, on-track crosswind event, the use of the fully coupled system was unnecessary. A simplified, one-way coupled system, in which there is no feedback from the vehicle s dynamics to the aerodynamic simulation was sufficient in order to capture the vehicle s path deviation. The realistic properties of the vehicle and accurately calibrated driver model prevented any large attitude changes whilst immersed in the gust, from which variations to the aerodynamics could arise. It was suggested that this system may be more suited to other vehicle geometries more sensitive to yaw motions or applications where a high positional accuracy of the vehicle is required

A drag coefficient for application to the WLTP driving cycle

The aerodynamic drag characteristics of a passenger car have, typically, been defined by a single parameter: the drag coefficient at a yaw angle of 0°. Although this has been acceptable in the past, it does not provide an accurate measure of the effect of aerodynamic drag on fuel consumption because the important influence of the wind has been excluded. The result of using drag coefficients at a yaw angle of 0° produces an underprediction of the aerodynamic component of fuel consumption that does not reflect the on-road conditions. An alternative measure of the aerodynamic drag should take into account the effect of non-zero yaw angles, and a variant of wind-averaged drag is suggested as the best option. A wind-averaged drag coefficient is usually derived for a particular vehicle speed using a representative wind speed distribution. In the particular case where the road speed distribution is specified, such as for a driving cycle to determine fuel economy, a relevant drag coefficient can be derived by using a weighted road speed. An effective drag coefficient is determined with this approach for a range of cars using the proposed test cycle for the Worldwide Harmonised Light Vehicle Test Procedure, WLTP. The wind input acting on the car has been updated for this paper using recent meteorological data and an understanding of the effect of a shear flow on the drag loading obtained from a computational fluid dynamics study. In order to determine the different mean wind velocities acting on the car, a terrain-related wind profile has also been applied to the various phases of the driving cycle. An overall drag coefficient is derived from the work done over the full cycle. This cycle-averaged drag coefficient is shown to be significantly higher than the nominal drag coefficient at a yaw angle of 0°

A study of computational methods for wake structure and base pressure prediction of a generic SUV model with fixed and rotating wheels

This study is an evaluation of computational methods in reproducing experimental data for a generic SUV geometry and an assessment on the influence of fixed and rotating wheels for this geometry. Initially, comparisons are made in wake structure and base pressures between several CFD codes and experimental data. It was shown that steady-state RANS methods are unsuitable for this geometry due to a large scale unsteadiness in the wake caused by separation at the sharp trailing edge and rear wheel wake interactions. URANS offered no improvements in wake prediction despite a significant increase in computational cost. DES and Lattice Boltzmann methods showed the best agreement with experimental results in both wake structure and base pressure, with LBM running in approximately a fifth of the time for DES

Phenylsulfonylacetic acid: condensations onto aryl aldehydes

<div><p>A study involving scope in the condensation reaction of phenylsulfonylacetic acid with a series of carbonyl derivatives has been conducted. Reactivity trends favor formation of the corresponding vinyl sulfones when working with aryl aldehydes. Electron-deficient aryl aldehydes outperform electron-rich aryl aldehydes. Negligible differences were noted when using electron-rich and electron-deficient arylsulfonylacetic acid derivatives. Post-run analyses of the reaction mixture reveal formation of a minor product which resulted from methylidene transfer onto the carbonyl derivative. Support of a Knoevenagel-type condensation followed by decarboxylation is provided.</p></div