The propeller is rotating at high speed and the Q cloud obtained shows a lot of red noise areas, what is the reason for this?

[wjsjtu123]

I set the propeller rotational speed to 4145r/min and then the resultant visualization process shows a lot of red noise areas.
The code is shown below, I don't know if the code is wrong or not.

[ProjectPhysX]

Hi @wjsjtu123,

some possible fixes:

• reduce lbm_u from 0.16f to 0.1f or lower - this is the blade tip velocity in LBM units, and it should not be much larger than 0.1f
• make sure that SUBGRID is enabled
• you can also adjust the color scale GRAPHICS_U_MAX to a larger value

Kind regards,
Moritz

[wjsjtu123]

Thank you very much the above problem has been solved and is due to the fact that my propeller tip linear velocity is well above the rendered velocity maximum of 0.25. but I have a new problem.

When performing a propeller rotational motion, I define a rotational motion around the x-axis with a rotational speed of 4145r/min, but in the voxelized motion, instead of following a fixed x-axis, the propeller will rotate periodically off-center, what is the cause of this, and how can I fix it?



My code is as follows

void main_setup() { // NACA X-57 lift propeller; required extensions in defines.hpp: FP16C, EQUILIBRIUM_BOUNDARIES, MOVING_BOUNDARIES, SUBGRID, INTERACTIVE_GRAPHICS or GRAPHICS
// ################################################################## define simulation box size, viscosity and volume force ###################################################################
	const uint3 lbm_N = resolution(float3(2.0f, 1.0f, 1.0f), 4000u); // input: simulation box aspect ratio and VRAM occupation in MB, output: grid resolution
	const float lbm_u = 0.11f;
	const float lbm_length = 0.5f*(float)lbm_N.x;
	const float si_n =4145.0f; //RPM of propeller
	const float si_n_t = 20.0f;
	const float si_T = (60.0f/si_n)si_n_t; // 20 revolutions of the propeller
	const uint lbm_dt = 30u; // revoxelize rotor every dt time steps
	const float si_length=0.984f;
	const float si_J = 0.6f; // Advance ratio
	const float si_D = 0.57592f; //propeller radius
	const float si_u = si_Jsi_D*(si_n/60.0f); //airspeed
	const float si_w_u = (si_npif/30.0f)(si_D0.5f); //propeller linear velocity
	const float si_nu=1.48E-5f, si_rho=1.225f;
	units.set_m_kg_s(lbm_length, lbm_u, 1.0f, si_length, si_u, si_rho);
	print_info("lbm_u="+to_string(units.u(si_u)));
	LBM lbm(lbm_N, 1u, 1u, 1u, units.nu(si_nu));
	// ###################################################################################### define geometry ######################################################################################
	Mesh fuselage = read_stl(get_exe_path()+"../stl/propeller_fuselage_semi.stl"); //
	Mesh* propeller = read_stl(get_exe_path()+"../stl/propeller_semi.stl"); //
	const float scale = lbm_length/fuselage->get_bounding_box_size().x; // scale body and rotors to simulation box size
	fuselage->scale(scale);
	propeller->scale(scale);
	const float3 offset = lbm.center()-fuselage->get_bounding_box_center(); // move body and rotors to simulation box center
	fuselage->translate(offset);
	propeller->translate(offset);
	fuselage->set_center(fuselage->get_bounding_box_center()); // set center of meshes to their bounding box center
	propeller->set_center(propeller->get_bounding_box_center());
	print_info("diameter="+to_string(units.x(si_D)));
	print_info("propeller_max_size="+to_string(propeller->get_max_size()));
	const float propeller_radius=0.5funits.x(si_D), propeller_omega=(units.si_u(si_w_u))/(propeller_radius), propeller_domega=propeller_omega(float)lbm_dt;
	lbm.voxelize_mesh_on_device(fuselage);
	//lbm.voxelize_mesh_on_device(propeller, TYPE_S, propeller->get_center(), float3(0.0f), float3(propeller_omega, 0.0f, 0.0f)); // revoxelize mesh on GPU
	const uint Nx=lbm.get_Nx(), Ny=lbm.get_Ny(), Nz=lbm.get_Nz(); parallel_for(lbm.get_N(), [&](ulong n) { uint x=0u, y=0u, z=0u; lbm.coordinates(n, x, y, z);
	if(lbm.flags[n]!=TYPE_S) lbm.u.x[n] = lbm_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
	}); // ####################################################################### run simulation, export images and data ##########################################################################
	lbm.graphics.visualization_modes = VIS_FLAG_SURFACE|VIS_Q_CRITERION;
	lbm.run(0u); // initialize simulation
	while(lbm.get_t()<=units.t(si_T)) { // main simulation loop
		lbm.voxelize_mesh_on_device(propeller, TYPE_S, propeller->get_center(), float3(0.0f), float3(propeller_omega, 0.0f, 0.0f)); // revoxelize mesh on GPU
		lbm.run(lbm_dt); // run dt time steps
		propeller->rotate(float3x3(float3(1.0f, 0.0f, 0.0f), propeller_domega)); // rotate mesh
#if defined(GRAPHICS) && !defined(INTERACTIVE_GRAPHICS)
		if(lbm.graphics.next_frame(units.t(si_T), 10.0f)) {
			lbm.graphics.set_camera_free(float3(0.528513f*(float)Nx, 0.102095f*(float)Ny, 1.302283f*(float)Nz), 16.0f, 47.0f, 96.0f);
			lbm.graphics.write_frame(get_exe_path()+"export/a/");
			lbm.graphics.set_camera_free(float3(0.0f*(float)Nx, -0.114244f*(float)Ny, 0.543265f*(float)Nz), 90.0f+degrees((float)lbm.get_t()/(float)lbm_dtmain_domega), 36.0f, 120.0f);
			lbm.graphics.write_frame(get_exe_path()+"export/b/");
			lbm.graphics.set_camera_free(float3(0.557719f(float)Nx, -0.503388f*(float)Ny, -0.591976f*(float)Nz), -43.0f, -21.0f, 75.0f);
			lbm.graphics.write_frame(get_exe_path()+"export/c/");
			lbm.graphics.set_camera_centered(58.0f, 9.0f, 88.0f, 1.648722f);
			lbm.graphics.write_frame(get_exe_path()+"export/d/");
			lbm.graphics.set_camera_centered(0.0f, 90.0f, 100.0f, 1.100000f);
			lbm.graphics.write_frame(get_exe_path()+"export/e/");
			lbm.graphics.set_camera_free(float3(0.001612f*(float)Nx, 0.523852f*(float)Ny, 0.992613f*(float)Nz), 90.0f, 37.0f, 94.0f);
			lbm.graphics.write_frame(get_exe_path()+"export/f/");
		}
#endif // GRAPHICS && !INTERACTIVE_GRAPHICS
	}
}

[ProjectPhysX]

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