Posted: September 13th, 2017

Vehicle Aerodynamics and Air Management

Vehicle Aerodynamics and Air Management

Assignment Title where appropriate: Optimal design of a cab deflector for a semi-trailer

ASSIGNMENT BRIEF

Introduction
Understanding of aerodynamic and road loads is very important in establishing acceleration and braking characteristics, stability as well as fuel consumption characteristics of vehicles. More and more semi-trailers have started to use cab deflectors to minimise drag and hence fuel consumption. Therefore, aerodynamic characteristics of such deflectors need to be evaluated very carefully.

Specifications:
It is expected that students will develop a computer model of a semi-trailer of their own choice(without a cab deflector)  using CAD Package of their own choice. After developing the computer model students are expected to investigate possibility of using a cab deflector to reduce drag and hence fuel consumption  using CFD package FLUENT.

1) Students are required to analyse the effect of presence of a cab deflector on drag force acting on the vehicle. The design velocity should be 55 MPH should act opposite to the direction of motion of the vehicle. Calculate drag force on all faces of the semi-trailer for both with and without cab deflector simulations.

2) Investigate the response of the vehicle if flowing air approaches the vehicle at an angle. Assuming flow velocity to be same, compute drag, lift and side forces acting on the vehicle for flow angles of 150 and 30o .

4)  Investigate the effect of length of development of flow (take two different upstream lengths 20 x height of the vehicle and 30 x height of the vehicle) on the accuracy of results obtained. This analysis needs to be carried out at 55 MPH with air flow opposite to the semitrailer motion. Only use the model with cab deflector.

5) Investigate the effect of width of flow field around the vehicle (Take two different widths, 3 times the width of the vehicle and 10 times width of the vehicle.) on the accuracy of results. This analysis needs to be carried out at 55 MPH with air flow opposite to the semitrailer motion. Only use the model with cab deflector.

6) Design, develop and execute validation programme for the simulations carried out. For example, you may use Rapid prototype machine for developing a small scale model of the vehicle. This model could be tested in the wind tunnel. The other option may be to use the data published in the literature.

7) Based on the investigations above propose an optimal shape of the cab deflector. Clearly justify your choice.

The Report
The assignment report must have a formal structure and must include appropriate references (internet references may be included) and appendices.  The maximum word limit for the report is 4000 words. This excludes the title page, headers/footers, list of figures/tables etc., summary page and the appendix. The report is to be word processed and an electronic copy must be submitted via turnitin.
Guidance
Higher grades will be associated with reports which:
?    Make effective use of information from a sufficiently broad range of appropriate sources e.g. available prototype, books, journals, technical literature and the internet.  N.B. references should be seen as the evidence, which underpins the discussion and conclusions made in the report and not simply as sections to be copied.
?    Show understanding of the concepts used and explain any assumptions made in the analysis.
?    Follow a logical sequence and show in-depth analysis capability.
?    Include external features of the vehicle in the computer model.
?    Have a standard formal structure which makes good use of an appendix and make a clear distinction between references and bibliography.  Have a tidy, standard approach to layout and presentation (one style rather than several ). Make good use of images and figures.
?    Are original and interesting in their discussion and in their ideas and conclusions.

Figure 1: A typical CAD model of a semitrailer without a cab deflector
Assessment Chart

Item    Unsatisfactory    Satisfactory    Average    Good    Very good
Creation of geometry and Mesh 10%    Inclusion of figure only    Inclusion of figure with description of dimensions    Inclusion of figure with description and justification  of dimensions    Inclusion of figure with description and justification  of dimensions with steps in the creation model    Inclusion of figure with description and justification  of dimensions with steps in the creation model including justification of mesh used
Drag force results 20%    Simulation without explaining various elements    Description of boundary condition with simulation    Justification of boundary conditions with simulation    Justification of boundary conditions with simulation including  flow field analysis    Justification of boundary conditions with simulation including flow field analysis and establishing quantitative relationship among parameters of interest.
Side wind effect 20%    Simulation without explaining various elements    Description of boundary condition with simulation    Justification of boundary conditions with simulation    Justification of boundary conditions with simulation including flow field analysis    Justification of boundary conditions with simulation including  flow field analysis and establishing quantitative relationship among parameters of interest.
Effect of length of development of flow 10%    Simulation without explaining various elements    Description of boundary condition with simulation    Justification of boundary conditions with simulation    Justification of boundary conditions with simulation with flow field analysis    Justification of boundary conditions with simulation including flow field analysis and establishing quantitative relationship among parameters of interest.
Effect of flow field width 10%    Simulation without explaining various elements    Description of boundary condition with simulation    Justification of boundary conditions with simulation    Justification of boundary conditions with simulation with flow field analysis    Justification of boundary conditions with simulation including  flow field analysis and establishing quantitative relationship among parameters of interest
Validation      20 %    Validation without a proper validation strategy    Development of a validation strategy and execution    Development of a validation strategy and its execution including  establishing qualitative similarities    Development of a validation strategy and its execution and including establishing qualitative  and quantitative similarities    Development of a validation strategy and its execution and including establishing qualitative  and quantitative similarities with error estimates
Optimisation analysis 10%    Unstructured optimisation    Structured optimisation based on flow field analysis
Structured optimisation based on flow field analysis
with new flow simulation to show qualitative improvement    Structured optimisation based on flow field analysis
With new flow simulation to show quantitative improvement    Structured optimisation based on flow field analysis
With new flow simulation to show quantitative improvement. Developing a frame work for further optimisation