Add local timestep + CFL as volume output

[j-signorelli]

Proposed Changes

Added local timestep and local CFL as volume output for both the flow and turbulence variables

Related Work

In relation to #2056

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[pcarruscag]

Thanks, please add yourself to AUTHORS.md

[j-signorelli]

Hi @pcarruscag, just wanted to follow up with you on something about this: it looks like to me that the volume output $\Delta t$'s are nondimensional. Would it be worthwhile to mention this in the SU2_CFD -d call? Or even just calculate the actual physical time as the volume output alternatively? This may be confusing.

[pcarruscag]

Our reference for time is always 1 so they should match physical time even if they appear non-dimensional. What area of the code made it look nondimensional?

[j-signorelli]

Oh interesting, just to be fully complete here's what made me think that:

1.I have a well-converged steady-state solution and outputted the minimum DT's for each cell when running with a CFL=1.0, no adaptive. I was unable to restart this for an unsteady one with no changes in BCs without using a DT orders-of-magnitude smaller.

2. When I run /Tutorials/compressible_flow/Turbulent_OneraM6 with MIN_DELTA_TIME set as a screen output, I get orders-of-magnitude different final timestep when I run with REF_DIMENSIONALIZATION= DIMENSIONAL instead of FREESTREAM_VEL_EQ_ONE.

3. When I run SU2_CFD -d on the /Tutorials/compressible_flow/Unsteady_NACA0012 example using FREESTREAM_VEL_EQ_ONE I see the attached image below, which appears to nondimensionalize using length/velocity.

4. I also looked briefly at the code it appeared that the calculations were using nondimensional values; here's what I looked at:

Setting of local timestep:

SU2/SU2_CFD/include/solvers/CFVMFlowSolverBase.hpp

Lines 506 to 522 in b80e4ce

	if (Vol != 0.0) {
	su2double Local_Delta_Time = nodes->GetLocalCFL(iPoint)*Vol / nodes->GetMax_Lambda_Inv(iPoint);
	if(viscous) {
	su2double dt_visc = nodes->GetLocalCFL(iPoint)*K_v*Vol*Vol / nodes->GetMax_Lambda_Visc(iPoint);
	Local_Delta_Time = min(Local_Delta_Time, dt_visc);
	}
	minDt = min(minDt, Local_Delta_Time);
	maxDt = max(maxDt, Local_Delta_Time);
	nodes->SetDelta_Time(iPoint, min(Local_Delta_Time, config->GetMax_DeltaTime()));
	}
	else {
	nodes->SetDelta_Time(iPoint,0.0);
	}
	}

Calculation of Lambda's:

SU2/SU2_CFD/include/solvers/CFVMFlowSolverBase.hpp

Lines 413 to 444 in b80e4ce

	auto jPoint = geometry->nodes->GetPoint(iPoint,iNeigh);
	auto iEdge = geometry->nodes->GetEdge(iPoint,iNeigh);
	auto Normal = geometry->edges->GetNormal(iEdge);
	auto Area2 = GeometryToolbox::SquaredNorm(nDim, Normal);
	/*--- Mean Values ---*/
	su2double Mean_ProjVel = 0.5 * (nodes->GetProjVel(iPoint,Normal) + nodes->GetProjVel(jPoint,Normal));
	su2double Mean_SoundSpeed = soundSpeed(*nodes, iPoint, jPoint) * sqrt(Area2);
	/*--- Adjustment for grid movement ---*/
	if (dynamic_grid) {
	const su2double *GridVel_i = geometry->nodes->GetGridVel(iPoint);
	const su2double *GridVel_j = geometry->nodes->GetGridVel(jPoint);
	for (unsigned short iDim = 0; iDim < nDim; iDim++)
	Mean_ProjVel -= 0.5 * (GridVel_i[iDim] + GridVel_j[iDim]) * Normal[iDim];
	}
	/*--- Inviscid contribution ---*/
	su2double Lambda = fabs(Mean_ProjVel) + Mean_SoundSpeed;
	nodes->AddMax_Lambda_Inv(iPoint,Lambda);
	/*--- Viscous contribution ---*/
	if (!viscous) continue;
	Lambda = lambdaVisc(*nodes, iPoint, jPoint) * Area2;
	nodes->AddMax_Lambda_Visc(iPoint, Lambda);

GetProjVel:

SU2/SU2_CFD/include/variables/CEulerVariable.hpp

Lines 244 to 254 in b80e4ce

	/*!
	* \brief Get the projected velocity in a unitary vector direction (compressible solver).
	* \param[in] val_vector - Direction of projection.
	* \return Value of the projected velocity.
	*/
	inline su2double GetProjVel(unsigned long iPoint, const su2double *val_vector) const final {
	su2double ProjVel = 0.0;
	for (unsigned long iDim = 0; iDim < nDim; iDim++)
	ProjVel += Primitive(iPoint,iDim+indices.Velocity())*val_vector[iDim];
	return ProjVel;
	}

Then at this point admittedly I just assumed that the MatrixType Primitive of CEulerVariable was indeed nondimensional. I am not familiar with where/when data is stored/updated throughout SU2 as nondimensional v dimensional.

[pcarruscag]

You are right, but in nondim mode all outputs are the nondim ones, so this is consistent.

[j-signorelli]

Would it be worthwhile to output the time step reference line for steady simulations in the "Solver Preprocessing" section as well then? This is only done for unsteady simulations.

[pcarruscag]

Sure sounds good