Wind flow over simplified mountain - please help me to set it up

Using SimScale Fluid Flow / CFD
1

I have tried to simulate wind flow over a simple hill. Results are not quite what I expected and raised some questions:

  1. Can I use small model of the hill (2000mm) with 5mm/s wind or or should I use full size model 2000m tall with 5m/s wind? If I can use a small model are there any other adjustments to be made (like density of the air etc)
  2. what should be the top boundary condition, wall or pressure outlet?
  3. Should I use non compressible or compressible simulation?
  4. How to include the effects of the gravity and the decreasing pressure at higher altitudes?

My objective is to create close to real flow with updraft on the windy side and down draft on the lee side. I would also expect to see some wave on the lee side which is often used by glider pilots to climb to high altitudes if wind is strong enough.

I have minimal simscale or simulation experience and I would appreciate any help I could get.

2

Hey there!

To answer your questions, with the aim of improving results:

  1. To use a smaller model, the scaling has to be done to maintain the Reynolds number. This is typically done by changing length and flow speed, not density.
  2. The slip wall boundary condition is a good choice, given that the wall is far away from the obstacle. A typical good distance would be 3 times the height of the mountain or more.
  3. Compressible simulation should be used at high speeds. Typically, at 0.3 mach or around 100 m/s wind speed.
  4. In incompressible simulation, gravity is not taken into account, as the density is uniform.

Please try adjusting these aspects and let me know if your desired effects are shown in the results.