Easy to Run FluidX3D

Compute Features

CFD model: Lattice-Boltzmann method

• Streaming (2/2):

  f₀^temp(x,t) = f₀(x, t)
  f_i^temp(x,t) = f_{(t%2 ? i : (i%2 ? i+1 : i-1))}(i%2 ? x : x-e_i, t)   for   i ∈ [1, q-1]

• Collision:

  ρ(x,t) = (Σ_i f_i^temp(x,t)) + 1
  
  u(x,t) = ¹∕_ρ(x,t) Σ_i c_i f_i^temp(x,t)
  
  f_i^eq-shifted(x,t) = w_i ρ · (^(u_°c_i)2∕_(2c⁴) - ^(u_°u)∕_(2c²) + ^(u_°c_i)∕_c²) + w_i (ρ-1)
  
  f_i^temp(x, t+Δt) = f_i^temp(x,t) + Ω_i(f_i^temp(x,t), f_i^eq-shifted(x,t), τ)

• Streaming (1/2):

  f₀(x, t+Δt) = f₀^temp(x, t+Δt)
  f_{(t%2 ? (i%2 ? i+1 : i-1) : i)}(i%2 ? x+e_i : x, t+Δt) = f_i^temp(x, t+Δt)   for   i ∈ [1, q-1]

---

Velocity Sets:

• D2Q9
• D3Q15
• D3Q19 (default)
• D3Q27

Collision Operators:

• Single-relaxation-time (SRT/BGK) (default)
• Two-relaxation-time (TRT)

Only 8 flag bits per lattice point (can be used independently / at the same time):

• TYPE_S (stationary or moving) solid boundaries
• TYPE_E equilibrium boundaries (inflow/outflow)
• TYPE_T temperature boundaries
• TYPE_F free surface (fluid)
• TYPE_I free surface (interface)
• TYPE_G free surface (gas)
• TYPE_X remaining for custom use or further extensions
• TYPE_Y remaining for custom use or further extensions

Setup

Clone this repository:

git clone https://github.com/morkev/FluidX3D-easy-run.git

Go to the stl folder, and add the .stl file (or compatible format) there.

Declare whatever file you what to simulate in void main_setup() located in setup.cpp:

void main_setup() {
	// ######################################################### define simulation box size, viscosity and volume force ############################################################################
	const uint L = 256u;
	const float Re = 1000000.0f;
	const float u = 0.1f;
	LBM lbm(L, L*3u, L/2u, units.nu_from_Re(Re, (float)L, u));
	// #############################################################################################################################################################################################
	const float size = 1.75f*(float)L;
	const float3 center = float3(lbm.center().x, 0.52f*size, lbm.center().z+0.03f*size);
	// #############################################################################################################################################################################################
	// QUICK ROTATION FOR OBJECT ALIGNMENT
	// const float3x3 rotation = float3x3(float3(1, 0, 0), radians(-0.0f))*float3x3(float3(0, 0, 1), radians(270.0f))*float3x3(float3(1, 0, 0), radians(0.0f));
	// #############################################################################################################################################################################################
	const float3x3 rotation = float3x3(float3(1, 0, 0), radians(-10.0f))*float3x3(float3(0, 0, 1), radians(90.0f))*float3x3(float3(1, 0, 0), radians(90.0f));
	lbm.voxelize_stl(get_exe_path()+"../stl/F117.stl", center, rotation, size); // replace F117.stl with your file
	const uint N=lbm.get_N(), Nx=lbm.get_Nx(), Ny=lbm.get_Ny(), Nz=lbm.get_Nz(); for(uint n=0u, x=0u, y=0u, z=0u; n<N; n++, lbm.coordinates(n, x, y, z)) {
		// ########################################################################### define geometry #############################################################################################
		if(lbm.flags[n]!=TYPE_S) lbm.u.y[n] = u;
		if(x==0u||x==Nx-1u||y==0u||y==Ny-1u||z==0u||z==Nz-1u) lbm.flags[n] = TYPE_E; // all non periodic
	}	// #########################################################################################################################################################################################
	key_4 = true;
	lbm.run();
} /**/

Compatibility

• Works in Windows, Linux with C++17
• Supports importing and voxelizing triangle meshes from binary .stl files
• Supports exporting volumetric data as binary .vtk files
• Supports exporting rendered frames as .png/.qoi/.bmp files; time-consuming image encoding is handled in parallel on the CPU while the simulation on GPU can continue without delay

References

• Lehmann, M.: Esoteric Pull and Esoteric Push: Two Simple In-Place Streaming Schemes for the Lattice Boltzmann Method on GPUs. Computation, 10, 92, (2022)
• Lehmann, M., Krause, M., Amati, G., Sega, M., Harting, J. and Gekle, S.: Accuracy and performance of the lattice Boltzmann method with 64-bit, 32-bit, and customized 16-bit number formats. Phys. Rev. E 106, 015308, (2022)
• Lehmann, M.: Combined scientific CFD simulation and interactive raytracing with OpenCL. IWOCL'22: International Workshop on OpenCL, 3, 1-2, (2022)
• Lehmann, M., Oehlschlägel, L.M., Häusl, F., Held, A. and Gekle, S.: Ejection of marine microplastics by raindrops: a computational and experimental study. Micropl.&Nanopl. 1, 18, (2021)
• Lehmann, M.: High Performance Free Surface LBM on GPUs. Master's thesis, (2019)
• Lehmann, M. and Gekle, S.: Analytic Solution to the Piecewise Linear Interface Construction Problem and Its Application in Curvature Calculation for Volume-of-Fluid Simulation Codes. Computation, 10, 21, (2022)

Contact

• This is a fork of FluidX3D, developed by Dr. Moritz Lehmann [email protected].
• This is a ready to run version for those that don't have a heavy coding background, modified by Kevin Mora [email protected].