Computational simulations of unsteady flow field and spray impingement on a simplified automotive geometry

Accurately predicting vehicle soiling is important for maintaining a clear view for the driver and on board camera and sensor systems. In this work we study the soiling process on a scale model of generic SUV body, which is a vehicle type particularly susceptible to base contamination. The Spalart-Allmaras formulation of the IDDES model is used to compute the continuous phase and the dispersed phase is computed using Lagrangian particle tracking, both concurrently with the flow-field, and also as a post-processing approach using time averaged statistical information of turbulence in a stochastic dispersion model. The results are compared against experimental data and the discrepancies discussed with regard to the predicted and measured flow field and base pressure distribution. Good agreement with experiment is shown for the contamination pattern using the fully unsteady method, but the more economic stochastic model does not recover some important details. This is attributed to the role of spatially correlated flow structures around the wheel in entraining particles into the wake that the stochastic model cannot accurately represent. This leads to the conclusion that base soiling is a function of unsteady modes, elimination of which may potentially reduce spray deposition

Intelligent energy management in hybrid electric vehicles

The modelling and simulation approach is employed to develop an intelligent energy management system for hybrid electric vehicles. The aim is to optimize fuel consumption and reduce emissions. An analysis of the role of drivetrain, energy management control strategy and the associated impacts on the fuel consumption with combined wind/drag, slope, rolling, and accessories loads are included.<br /

Crosswind stability of vehicles under nonstationary wind excitation

This work has studied the crosswind stability of vehicles under nonstationary wind excitation in various scenarios. Railway vehicles running on curved and straight track with varying vehicle speed are studied. Road vehicles are classified into different categories. For each vehicle class, a corresponding worst-case vehicle model has been built. As the wind excitation on the vehicle is a stochastic process, a risk analysis has to be carried out and failure probabilities are computed and analyzed

Aerodynamic CFD Based Optimization of Police Car Using Bezier Curves

This paper investigates the optimization of the aerodynamic design of a police car, BMW 5-series which is popular police force across the UK. A Bezier curve fitting approach is proposed as a tool to improve the existing design of the warning light cluster in order to reduce drag. A formal optimization technique based on Computational Fluid Dynamics (CFD) and moving least squares (MLS) is used to determine the control points for the approximated curve to cover the light-bar and streamline the shape of the roof. The results clearly show that improving the aerodynamic design of the roofs will offer an important opportunity for reducing the fuel consumption and emissions for police vehicles. The optimized police car has 30% less drag than the non-optimized counter-part

On the need for a nonlinear subscale turbulence term in POD models as exemplified for a high Reynolds number flow over an Ahmed body

We investigate a hierarchy of eddy-viscosity terms in POD Galerkin models to account for a large fraction of unresolved fluctuation energy. These Galerkin methods are applied to Large Eddy Simulation data for a flow around the vehicle-like bluff body call Ahmed body. This flow has three challenges for any reduced-order model: a high Reynolds number, coherent structures with broadband frequency dynamics, and meta-stable asymmetric base flow states. The Galerkin models are found to be most accurate with modal eddy viscosities as proposed by Rempfer & Fasel (1994). Robustness of the model solution with respect to initial conditions, eddy viscosity values and model order is only achieved for state-dependent eddy viscosities as proposed by Noack, Morzynski & Tadmor (2011). Only the POD system with state-dependent modal eddy viscosities can address all challenges of the flow characteristics. All parameters are analytically derived from the Navier-Stokes based balance equations with the available data. We arrive at simple general guidelines for robust and accurate POD models which can be expected to hold for a large class of turbulent flows.Comment: Submitted to the Journal of Fluid Mechanic

Crosswind stability of vehicles under nonstationary wind excitation

This work has studied the crosswind stability of vehicles under nonstationary wind excitation in various scenarios. Railway vehicles running on curved and straight track with varying vehicle speed are studied. Road vehicles are classified into different categories. For each vehicle class, a corresponding worst-case vehicle model has been built. As the wind excitation on the vehicle is a stochastic process, a risk analysis has to be carried out and failure probabilities are computed and analyzed

An investigation of road vehicle rear surface contamination and its simulation

Vehicle surface contamination is an important design consideration as it affects aesthetic appearance, driver s vision and the performance of the onboard camera and sensor systems. This work investigates the soiling process and the requirements for credible numerical simulation of the rear surface contamination for two quarter-scale generic car-like bluff bodies, which represent a vehicle type particularly susceptible to this type of contamination. It was shown that the accurate prediction of the mean flow field is a prerequisite for credible soiling estimation. However, modelling the full unsteady behaviour of particle motion with concurrent particle tracking is crucial in order to accurately capture the details of soiling, which is highly unsteady in nature. It was shown that the spray generally entrains into the wake behind the core of the bottom wake vortex and the details of deposition are controlled by the wake structure and the size and orientation of the ring vortex. It was shown that the modelling of secondary spray processes, although computationally expensive, may be important as they tend to change the properties of spray and affect its dynamics. Consideration of realistic boundary conditions, such as the rotating tyres and ground motion was also shown to affect the spray. Wheel rotation increases deposition and the vertical distribution of spray on the base. The ground motion, on the other hand, leads to a wider contamination pattern. An investigation into the tyre spray modelling methods showed that the spray generated behind the contact patch is primarily responsible for the rear surface contamination. Therefore, this study suggested that the tyre spray model currently in use by industrial companies and researchers could potentially be simplified, which would result in a reduced computational effort and would speed up computations of vehicle surface contamination

Condition Monitoring of High-Sided Tractor-Trailer Units under Gusty Crosswind Conditions

It is well established that under gusty crosswind conditions, vehicle aerodynamic forces can lead to sudden changes in vehicle dynamics and stability. Large class vehicles, in particular, are more prone to rollover accidents in strong crosswind situations, especially at cruising speeds. It is therefore essential to conduct detailed investigations on the aerodynamic performance of commercial vehicles under crosswind conditions in order to improve their crosswind stability. This study predicts unsteady aerodynamic forces on a high-sided tractor-trailer unit exposed to gusty crosswind conditions. Although natural wind gusts are highly stochastic phenomena, and have a large variability in types and origins, this investigation suggests using deterministic gust model in combination with Computational Fluid Dynamics (CFD) based approach, using Large Eddy simulation (LES) for modeling air turbulence. Crosswind scenario with gusts of exponential shape, as specified in the Technical Specification for Interoperability (TSI), has been presented in the present study. A series of time-dependent aerodynamic interactions on the tractor-trailer unit have been recorded and investigated through the visualization of instantaneous gust flow structures around the truck-trailer unit. The results show that the TSI gust scenario has significant unsteady effects on the side aerodynamic force and the roll moment of the vehicle. Furthermore, there are significant variations in aerodynamic loads, consistent with the gust’s strength