# Optimal design of a diffuser for a semi-trailer

 Register Blogs Members List Search Today's Posts Mark Forums Read

 May 5, 2016, 09:10 Optimal design of a diffuser for a semi-trailer #1 New Member   StephC Join Date: May 2016 Posts: 1 Rep Power: 0 Hi, i'm a novice in CFD and will really love assistance in this project. I need a freelancer who can do this well and wouldn't mind negotiating a fee for it. Please contact me on stephc4real@gmail.com. Urgently waiting for a feedback 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 diffusers to minimise drag and hence fuel consumption. Therefore, aerodynamic characteristics of such diffusers need to be evaluated very carefully. Specifications: It is expected that you will develop a computer model of a semi-trailer of your own choice (without a diffuser) using CAD Package of your own choice. After developing the computer model you are expected to investigate possibility of using a diffuser to reduce drag and hence fuel consumption using CFD package ANSYS. 1) Required to analyse the effect of presence of a diffuser 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 upto 45 degrees. Choose minimum two side wind angles on both semi-trailers.. 4) Investigate the effect of length of development of flow (take two different upstream lengths 40 x height of the vehicle and 80 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 diffuser. 5) Investigate the effect of width of flow field around the vehicle (Take two different widths, 5 times the width of the vehicle and 20 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 diffuser. 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. You may validate using analytical methods as well. 7) Based on the investigations above propose an optimal shape of the diffuser. Clearly justify your choice.

May 6, 2016, 02:36
#2
Member

Join Date: May 2016
Posts: 55
Rep Power: 10
Hi StephC,

1) the velocity you mentioned 55 miles per hour, turned out as nearly 25 m/s. This velocity is very very less than Mach 0.3, hence this is a case of incompressible flow. Usual formulae for drag can be used for investigation

2) Aerodynamic flow and applied forces has to be measured if angle of attach changes slightly.

3) Details about flow development and (obviously) the grid independent analysis needs to be carried out at 55 MPH with air flow opposite to the semitrailer motion

4) Investigate the effect of width of flow field around the vehicle

5) Optimize the shape of the diffuser.

Further, I would like to mention that, we can surely help you in completing this analysis. A formal introduction about Workshop Technologies has been sent to your email ID. Kindly check and confirm.

You can also visit us at: http://workshopwale.com

Quote:
 Originally Posted by StephC Hi, i'm a novice in CFD and will really love assistance in this project. I need a freelancer who can do this well and wouldn't mind negotiating a fee for it. Please contact me on stephc4real@gmail.com. Urgently waiting for a feedback 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 diffusers to minimise drag and hence fuel consumption. Therefore, aerodynamic characteristics of such diffusers need to be evaluated very carefully. Specifications: It is expected that you will develop a computer model of a semi-trailer of your own choice (without a diffuser) using CAD Package of your own choice. After developing the computer model you are expected to investigate possibility of using a diffuser to reduce drag and hence fuel consumption using CFD package ANSYS. 1) Required to analyse the effect of presence of a diffuser 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 upto 45 degrees. Choose minimum two side wind angles on both semi-trailers.. 4) Investigate the effect of length of development of flow (take two different upstream lengths 40 x height of the vehicle and 80 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 diffuser. 5) Investigate the effect of width of flow field around the vehicle (Take two different widths, 5 times the width of the vehicle and 20 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 diffuser. 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. You may validate using analytical methods as well. 7) Based on the investigations above propose an optimal shape of the diffuser. Clearly justify your choice.

 May 11, 2016, 03:16 Matsyateknik Engineering Solutions for CFD problems #3 New Member     MatsyaTeknik Engineering Solutions Join Date: Sep 2014 Location: Hyderabad Posts: 8 Rep Power: 11 We are "Matsyateknik Engineering Solutions", a private regulatory compliance and CFD solution company with the joint collaboration of "Concurrent Analysis Pvt Ltd", which is a well established Engineering services provider for CFD & FEA analysis. Should you be interested in this cooperation or have any questions in this regard, please feel free to give me a call email at contact@matsyateknik.com. We an expertise in solving various CFD Problems using both CFX and fluent. You can mail us further details regarding your work and we will work on resolving your quires. Regards, Team Matsyateknik Engineering Solutions. __________________ MatsyaTeknik Engineering Solutions