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Fixed orifice with inertia, automatic R value

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grillkol
2026-05-09 14:43:49 +02:00
parent 1489f278dc
commit a9e1c966b5
5 changed files with 223 additions and 173 deletions
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50
Scenarios/HelmholtzScenario.cs
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@@ -38,7 +38,7 @@ namespace FluidSim.Tests
int neckCells = 20;
// --- Volume (cavity) ---
float initialPressure = 1.2f * 101325f; // slight overpressure
float initialPressure = 1.1f * 101325f; // slight overpressure
float initialTemperature = 300f;
cavity = new Volume0D(cavityVolume, initialPressure, initialTemperature);
cavityPort = cavity.CreatePort();
@@ -56,24 +56,16 @@ namespace FluidSim.Tests
float rho0 = 101325f / (287f * 300f);
pipeSystem = new PipeSystem(neckCells, pipeStart, pipeEnd, areas, dxs, rho0, 0f, 101325f);
pipeSystem.DampingMultiplier = 500f;
// --- Boundary system ---
boundaries = new BoundarySystem(pipeSystem, maxOrifices: 1, maxOpenEnds: 1);
float ComputeResistance(float decayTimeSeconds, float rho, float L_eff, float A)
{
// R = 2 * rho * L_eff / (A * decayTimeSeconds)
return 2f * rho * L_eff / (A * MathF.Max(decayTimeSeconds, 1e-6f));
}
// Use steady orifice – the pipe already provides the inertia
// Standard orifice with built‑in minor loss (K = 0.5) – no inertance needed
boundaries.AddOrificeWithInertance(
cavityPort, pipeIndex: 0, isLeftEnd: true,
areaIndex: cavityOrificeIdx,
dischargeCoeff: 0.9f,
effectiveLength: neckLength, // physical length (or L_eff)
lossCoefficient: 7000 // start with this, adjust for decay time
effectiveLength: neckLength // physical neck length
);
// Open end at right side of pipe
@@ -83,8 +75,7 @@ namespace FluidSim.Tests
boundaries.SetOrificeAreas(orificeAreas);
// --- Solver ---
// Slightly higher sub‑step count to ensure stability of the resonant oscillation
solver = new Solver { SubStepCount = 6, EnableProfiling = false };
solver = new Solver { SubStepCount = 8, EnableProfiling = false };
solver.SetTimeStep(dt);
solver.SetPipeSystem(pipeSystem);
solver.SetBoundarySystem(boundaries);
@@ -99,43 +90,12 @@ namespace FluidSim.Tests
public override float Process()
{
stepCount++;
if (stepCount <= 8192) return 0f; // let buffer pre‑fill
solver.Step();
stepCount++;
float flow = boundaries.GetOpenEndMassFlow(openEndIdx);
float sample = soundProcessor.Process(flow);
if (stepCount % 10000 == 0)
{
float cavityP = cavity.Pressure;
float cavityT = cavity.Temperature;
float cavityRho = cavity.Density;
float cCavity = MathF.Sqrt(1.4f * cavityP / MathF.Max(cavityRho, 1e-12f));
// Temperature in the middle of the neck
int midCell = 10;
float pMid = pipeSystem.GetCellPressure(midCell);
float rhoMid = pipeSystem.GetCellDensity(midCell);
float tMid = pMid / MathF.Max(rhoMid * 287f, 1e-12f);
// Neck effective length (physical + end correction)
float neckLen = 0.05f; // physical
float neckDia = 0.02f;
float neckArea = MathF.PI * 0.25f * neckDia * neckDia;
float endCorr = 0.85f * neckDia; // unflanged end
float L_eff = neckLen + endCorr;
// Theoretical Helmholtz frequency from current cavity sound speed
float fHelmholtz = cCavity / (2f * MathF.PI) *
MathF.Sqrt(neckArea / (cavity.Volume * L_eff));
Console.WriteLine(
$"Step {stepCount}: cav P={cavityP / 1e5f:F4} bar, T={cavityT:F1} K, " +
$"pipeMid T={tMid:F1} K, est f={fHelmholtz:F1} Hz");
}
return sample;
}