Experimental and Numerical Study of Parameters Affecting the Wake Dynamics of a Simplified Car: Effects of Roughness - Turbulence - Yaw Angle

Air quality is a major public health issue worldwide.Two origins can be identified for pollutant particles that emanated from road transport vehicles.The dynamics of exhaust and non-exhaust pollutants released into the atmosphere in the wake of passenger cars are still poorly understood. An enhanced understanding of these physical processes involved in the dispersion of pollutants is essential. The flow topology must be accurately described and analysed while both the flow and the interaction of the flow and particles must be better understood. Our ability to find solutions to either limit the infiltration of pollutants into car cabins (and thus reduce the exposure of the occupants) or to identify areas where they can accumulate (areas to be avoided by pedestrians and cyclists) depends on these issues. This is the context of this PhD project. 

Overview

 The PhD student will be testing these hypotheses:

• There is a strong effect of the vehicle shape on the wake flow and aerodynamic drag.

• There is a direct link between the topology of wake flow and dispersion of pollutants.

To test these two hypotheses, the PhD student will:
• Investigate the effects of different parameters on the wake flow such as yaw angle, vehicle shape (more realistic shapes), inflow turbulence, and ground roughness.
• Extend previous results on Ahmed bodies (simplified) to DrivAer models (realistic).
• Combine experiments and simulations based on prior work and initial developments.

Better understanding of how bi-stability flow phenomena could affect the wake flow in the context of pollutant dispersion is required. We do not yet fully understand the bi-stability flow phenomena for DrivAer models. The influence of the geometric scale and ability to transpose from small scale to large scale of the geometry. Prior studies mostly focused on drag reduction rather than pollutant dispersion. This PhD project aims to fill this academic knowledge gap in the field by addressing health and environmental issues.

The intellectual contribution is to:
• Develop methodologies to analyse experimental data from different tools.
• Development/improvement of (new) data processing techniques.
• Get a better understanding of which key factors would affect particle dispersion.
• Share the new knowledge through publications with the wider scientific community.

What will you Learn

The main objectives of this project are:

• Characterisation of the flow developing in the wake of an Ahmed body (reference case). Both steady and unsteady studies will be conducted for different experimental conditions (yaw angles of the model), natures of the incident flow turbulence, and roughness of the ground). The results can be compared to available data in the literature (especially in the framework of the collaboration with Concordia University).

• Characterisation of the flow developing in the wake of a DrivAer model. Both steady and unsteady studies will be conducted for experimental conditions with different yaw angles, natures of the incident flow, and roughness of the ground. The results will be compared with those available in the literature.

• Study of the effect of a rolling road (relative movement of the ground) on the wake. To achieve this goal, measurements will be carried out at Cranfield using experimental conditions studied with a fixed floor at ESTACA. The influence of the car model, ground roughness, incident turbulence and yaw angle will be discussed.

• Characterisation of steady and unsteady flows (determination of the characteristic time and length scales of the flow). For this, we will rely on preliminary results obtained by Edwin Duran-Garcia which will be extended to the proposed PhD project. Additional developments may be made depending on the progress of the work.

• Numerical simulations will be carried out at Cranfield in the continuity of what is done by considering the new experimental developments. For these CFD studies, numerical tools and super computers at Cranfield and Loughborough will be available.

• On-road experimental data will be provided by industry (Emissions Analytics), which will enable us to bridge the gap between wind tunnel and actual road conditions.

Unique Selling Points

At Cranfield University (Shrivenham campus), the student will perform both experimental and computational research. At ESTACA (Bordeaux campus), the student will perform experimental research. The datasets of on-road measurements from Emissions Analytics will be used to bridge the gap between wind tunnel measurements and on-road realistic conditions. These datasets will be helpful to further improve our computational models. Loughborough University will provide access to wind tunnels and super computers. This will be helpful in terms of both experimental and computational work. They will also share their in-house codes and software licenses, which will be helpful to develop high-fidelity computational models that can accurately capture the bi-stability flow phenomena.

To carry out this PhD project, the student will undertake a detailed literature review of the subject (including specific details about the experimental set up and techniques, numerical schemes and simulations, turbulence models, boundary layer treatments, wind tunnels, simplified and realistic vehicle models, advanced data processing of experimental and computational datasets, wake flow unsteadiness, data convergence issues, etc.).

Location of Study

Based at the UK Defence Academy at Shrivenham in Oxfordshire, CDS is the academic provider to the UK Ministry of Defence for postgraduate education at the Defence Academy, training in engineering, science, acquisition, management and leadership.

Funding
This is a fully-funded, 3-year, full-time PhD studentship, which covers tuition fees at a UK level (£4,596 per year for 3 years), stipend (£19,000 per for 3 years), and running costs (£10,000 over a period of 3 years). These running costs include travel and subsistence, conference registration fees, laboratory consumables, and training.