CFD – Workbench

Workbench is a program I was introduced to digitally simulate, In our case, a rocket. This process would be used for both moving objects/viechles and still objects like buildings. This process would be expected for safety, this will collect loads of data to help imrove designs and learn new things. Its useful to learn a simulation like this as most of the time it’s the next best thing to real tests. We started by learning the construction of the rocket and what it needs.

 

Once the rocket is built in this software it can measure the dynamics. There is a huge range of settings that need to be set up. Our first look was Pressure inside the rocket.

Next was the pressure outside the rocket.

And others like velocity and streamline.

 

 

I was introduced to the wind tunnel to simulate aerodynamics. Wind tunnels are machines that provide a controllable flow field to investigate various flow phenomena to study effects of air moving over scaled test models. It is possible to measure velocity, vorticity, aerodynamic forces, moments and pressure acting on the test models, temperature around the models. 

Wind tunnels can be used for; cars on the road, planes in flight, submarines in water and new buildings. Helping measure aerodynamics can help choosing wing sizes on a plane or spoilers on the back of a car.

There are different types of wind tunnels, open and closed circuts, with different flow speeds. A closed circuit means there is a full flow. The flow is clockwise, the contraction section aligns the flow, then the test section has mountable points for model. It will the circle back round.

When looking at the wind tunnel, I could recognise the parts from the diagram, with the contraction, test section, and diffuser. The rest looped underground. I then planned for some testing.

 

There were different shapes to present how would the tunnel react to them. To start up the testing I needed to note down the Temperature and air pressure before and after the testing for quality control. 

Before Tests After Tests
Ambient temperature 20 20
Ambient air pressure  767 767

After the startup observations we then started testing different shapes. These were four tests, this is exampling how them slight differences goes along way. Below is the three profiles I used. My fourth reading with the tunnel in reverse flowing the other way.

 

Calibration (mount only) RPM Flow Velocity Drag Force
0 0 0
200 4.0 0.03
400 9.4 0.24
600 15.2 0.71
800 20.9 1.37
First Profile RPM Flow Velocity Drag Force
0 0 0
200 4.0 0.07
400 9.3 0.44
600 15.3 1.24
800 20.8 2.39
Second Profile RPM Flow Velocity Drag Force
0 0 0
200 3.7 0.05
400 9.4 0.43
600 14.9 1.15
800 20.8 2.27
Third Profile RPM Flow Velocity Drag Force
0 0 0
200 3.9 0.05
400 9.2 0.3
600 15.1 0.84
800 20.1 1.61
Fourth Profile RPM Flow Velocity Drag Force
0 0 0
200 4 0.08
400 9.5 0.35
600 15 0.9
800 20.8 1.72

Determining Center of gravity and pressure

Each component has (some) weight and are located (some) distance from a reference.

The centre of gravity multiplied by the wight is equal to the weight multiplied distance of all the components away from the reference. 

The equation looks like this: cg W = DaWa+DbWb+DcWc+Dd+Wd…

Similar to centre of gravity. Each component has (Some) area located (Some) distance from a reference. The centre of pressure multiplied by the Area is equal to the area times distance for each component from the reference. 

This equation is : cp A = DaAa+DbAb+DcAc+DdAd…

The center of gravity is the point on witch the rocket will turn. And the center of pressure is the point where wind pressure balances out. This would mean that you would want the cg higher than the cp for a stable flight path, done buy adding weight higher up.