# 'Aerodynamic analysis of a Semi-Truck Trailer vehicle' simulation project by Ali_Arafat

#1

I created a new simulation project called 'Aerodynamic analysis of a Semi-Truck Trailer vehicle':

This project simulates airfow around a Semi-Truck with container trailer.

More of my public projects can be found here.

#2

## Description

Aerodynamics plays a significant role in the performance of heavy automotives. A good aerodynamic design helps augment the g-force and hence, the traction of the vehicle on the road, keeping risk of lift-off, skidding and resultant accidents at bay. Moreover, drag reduction can greatly decrease the specific fuel consumption of the vehicle, thereby reducing the carbon footprint and saving fuel cost in the bargain.

This is where Computational Fluid Dynamics (CFD) steps in. It helps us conduct a simulation of the airflow around the vehicle, computing the regions of high pressure, wind velocity and wake regions encompassing the vehicle under study.

## Project Goals

The project at hand intends to simulate external aerodynamics of a Semi-truck trailer vehicle via steady state turbulent flow analysis with the K-Omega SST model for turbulence modeling.

## Geometry

The source geometry includes a Semi-truck model with trailer and was provided by GrabCAD user Joerg Schmit. The geometry was simplified for external flow analysis and is shown in the figure below. The vehicle has the dimensions: 16.6 m x 3 m x 4 m (l x b x h).

## Meshes

The domain is assigned as 18 m upstream, 35 m downstream and 15 m in positive X and Y directions. To reduce the computational domain, a symmetry condition is taken along the flow direction. The domain is meshed using the Snappy-Hex-Mesh on the SimScale platform. The resulting mesh consists of approximately 6 million cells and is shown in the figure below.

## Simulations

An inlet velocity of 28 m/s is assumed with a pressure boundary condition at the outlet. The simulation jobs are run on 16 computing cores and take around 4.6 hours. The simulation analyzes the mean flow field around the vehicle.

## Results and Conclusions

The results below (processed on ParaView) provide a good insight into the behaviour of the flow around the vehicle body. The figures show high pressure distribution on the front face and a large flow recirculation region behind the trailer.

Velocity contours

Velocity streamlines

Pressure distribution

#3

Hi Ali,

Nice work. Can you let me know the units of the Pressure plot you have shown above ?

Thank you.

Sachet

#4

Hi @sachet,

the units are:

\frac{m^2}{s^2}

You can also open Ali’s project and have a look at the post-processing. The units are always shown when activating the color bar.

Best,

Jousef

#5

Hi, @jousefm . Thanks for that. Actually when i looked at the post processing result evaluation section , it was blank. Can i know the pressure at the back of trailer plot in terms of pascal? Also in the above plot is it a relative pressure ? If it is then what is the reference pressure.

Thank you.

Sachet

#6

Hi @sachet,

could you provide me with a screenshot of this issue?

First of all units for the pressure in OpenFOAM depend on the solver. Incompressible solvers use m^2/s^2 (also known as kinematic pressure). Compressible solvers use Pa [kg/(m*s^2)] as far as I know.

So you could use the Calculator filter in the post-processing and multiply the pressure in m^2/s^2 with the density in order to get Pascal (this POST might be interesting for you).

Concerning your question about the pressure, you might have a look at this thread (Reference Pressure in Numerics)

If you still have questions, feel free to ask anytime!

Happy SimScaling!

Jousef

#7

@jousefm Hi , Thanks for replying. It seems that i need to download Paraview for using the post processor. I wanted to compare the pressure on the back of the truck trailer in this simulation with my simulation results. Is it possible for you to show me screen shot of the back part of the truck-trailer with the values in m^2/s^2 because the screen shot you provided does not show the pressure at the back part which i am mainly interested in.

Thank you.

Sachet

#8

Hi @sachet,

no you do not have to download Paraview necessarily. You can also create plots like I did in the integrated Post-Processing tool on SimScale.