I have been on the road a lot lately, and the weather gods have not been favoring my ventures. Bad weather coupled with monster semi-trucks have been causing a ton of anxiety while overtaking or just keeping up in the adjoining lane. Sharing the highways with many different kinds of semi-trucks made me realize not all of them had the same effects on vehicles around them. This lead me to wonder, “can there be simple changes to existing design? “. Changing design from ground up is simply out of question.
Well I fired up SOLIDWORKS and Flow Simulation to study air-flow around Semi-Trucks. There were two distinct types on the road, one that had side-skirts and one without. I used 65 mph as my test speed and then assumed perfect driving conditions, meaning no Chicago winds can blow side ways.
Now, with the test conditions and geometry established the task ahead was simple, use Flow Simulation to study the effects of side-skirts. I used the compare feature in Flow Simulation to see results side by side.
Image on the left is without side-skirt and image on the right is with side-skirts. You can see the difference, the side-skirts reduce turbulence significantly. Then came the thought of studying air-drag. I built an equation goal using the standard Drag-Coefficient formula.
The Drag Coefficient is defined as:
Cd = 2 x Drag Force / density x (velocity)^2 x Area
Drag Force by definition the force component in the direction of the flow velocity
The reference area depends on what type of drag coefficient is being measured. For automobiles and many other objects, the reference area is the projected frontal area of the vehicle.
Drag Coefficient came to be around 0.93. Please note this is taking into account front projected cabin area of semi-truck.
Ideally, one would like the truck to be the shape of an aerofoil or tear-drop. While extremely cool, it may not be as functional. I turned to the internet for some cool truck models.
What do you think of these cool looking trucks?
Product Manger – Simulation
Computer Aided Technology Inc.