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Known bad point (unphysical energy loss)

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This commit is contained in:
max
2026-05-02 17:40:43 +02:00
parent 9fc45224af
commit 650b993c2b
6 changed files with 89 additions and 91 deletions
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13
Core/OrificeBoundary.cs
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@@ -55,14 +55,19 @@ namespace FluidSim.Core
bool isLeftBoundary,
out double massFlux, out double momFlux, out double energyFlux)
{
// mass flow from pipe to volume (positive = pipe → volume)
double mdot = MassFlow(pPipe, rhoPipe, pVol, rhoVol, conn);
// ----- Compute STAGNATION pressures -----
double pStagPipe = pPipe + 0.5 * rhoPipe * uPipe * uPipe;
double pStagVol = pVol + 0.5 * rhoVol * uVol * uVol; // uVol is always 0 for your volumes
// Mass flow driven by stagnation pressure difference (positive = pipe→volume)
double mdot = MassFlow(pStagPipe, rhoPipe, pStagVol, rhoVol, conn);
// Limit mass flow to the amount that can leave/enter the pipe cell
double maxMdot = rhoPipe * pipeArea * 343.0;
if (Math.Abs(mdot) > maxMdot) mdot = Math.Sign(mdot) * maxMdot;
bool flowLeavesPipe = mdot > 0;
bool flowLeavesPipe = mdot > 0; // pipe → volume
double uFace, pFace, rhoFace;
double massFluxPerArea;
@@ -83,7 +88,7 @@ namespace FluidSim.Core
{ uFace = uVol; pFace = pVol; rhoFace = rhoVol; }
}
// Total enthalpy of the injected fluid (corrected: mass flux × total enthalpy)
// Total enthalpy of the injected fluid
double specificEnthalpy = (1.4 / (1.4 - 1.0)) * pFace / Math.Max(rhoFace, 1e-12);
double totalEnthalpy = specificEnthalpy + 0.5 * uFace * uFace;

71
Core/Simulation.cs
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@@ -6,58 +6,46 @@ namespace FluidSim.Core
{
public static class Simulation
{
private static Solver solver;
private static Volume0D volA, volB;
private static Pipe1D pipe;
private static Connection leftConn, rightConn; // dummy connections for orifice params
private static Connection connA, connB;
private static int stepCount;
private static double time;
private static double dt;
private static int stepCount;
public static void Initialize(int sampleRate)
{
dt = 1.0 / sampleRate;
double V = 5.0 * Units.L;
volA = new Volume0D(V, 1.1 * Units.atm, Units.Celsius(20), sampleRate);
volB = new Volume0D(V, 1.0 * Units.atm, Units.Celsius(20), sampleRate);
double length = 150 * Units.mm;
double diameter = 25 * Units.mm;
double area = Units.AreaFromDiameter(25, Units.mm);
int nCells = 10;
pipe = new Pipe1D(length, area, nCells, sampleRate);
pipe.SetUniformState(1.2, 0.0, 1.0 * Units.atm); // start at 1 atm
pipe.SetUniformState(volA.Density, 0.0, volA.Pressure);
pipe.FrictionFactor = 0.02;
// Dummy connections – only used for orifice parameters
leftConn = new Connection(null, null) { Area = area, DischargeCoefficient = 1.0, Gamma = 1.4 };
rightConn = new Connection(null, null) { Area = area, DischargeCoefficient = 1.0, Gamma = 1.4 };
// Connections with orifice area equal to pipe area (flange joint)
connA = new Connection(volA.Port, pipe.PortA) { Area = area, DischargeCoefficient = 1.0, Gamma = 1.4 };
connB = new Connection(pipe.PortB, volB.Port) { Area = area, DischargeCoefficient = 1.0, Gamma = 1.4 };
solver = new Solver();
solver.AddVolume(volA);
solver.AddVolume(volB);
solver.AddPipe(pipe);
solver.AddConnection(connA);
solver.AddConnection(connB);
}
public static float Process()
{
// Fixed boundary reservoirs
double pLeft = 1.1 * Units.atm;
double rhoLeft = 1.2;
double uLeft = 0.0;
double pRight = 1.0 * Units.atm;
double rhoRight = 1.2;
double uRight = 0.0;
// Compute boundary fluxes via orifice model
OrificeBoundary.PipeVolumeFlux(
pipe.GetLeftPressure(), pipe.GetLeftDensity(), 0.0,
pLeft, rhoLeft, uLeft,
leftConn, pipe.Area, true,
out double leftMassFlux, out double leftMomFlux, out double leftEnergyFlux);
OrificeBoundary.PipeVolumeFlux(
pipe.GetRightPressure(), pipe.GetRightDensity(), 0.0,
pRight, rhoRight, uRight,
rightConn, pipe.Area, false,
out double rightMassFlux, out double rightMomFlux, out double rightEnergyFlux);
pipe.SetLeftBoundaryFlux(leftMassFlux, leftMomFlux, leftEnergyFlux);
pipe.SetRightBoundaryFlux(rightMassFlux, rightMomFlux, rightEnergyFlux);
pipe.Simulate();
solver.Step();
time += dt;
stepCount++;
Log();
@@ -66,20 +54,13 @@ namespace FluidSim.Core
public static void Log()
{
if (stepCount <= 20 || stepCount % 50 == 0)
if (stepCount <= 50 || stepCount % 200 == 0)
{
Console.WriteLine($"Step {stepCount:D4} t = {time * 1e3:F3} ms");
for (int i = 0; i < pipe.GetCellCount(); i++)
{
double rho = pipe.GetCellDensity(i);
double p = pipe.GetCellPressure(i);
double u = pipe.GetCellVelocity(i);
Console.WriteLine($" Cell {i}: ρ={rho:F4} kg/m³ p={p / 1e5:F6} bar u={u:F3} m/s");
}
double leftFlow = pipe.PortA.MassFlowRate;
double rightFlow = pipe.PortB.MassFlowRate;
Console.WriteLine($" Left flow = {leftFlow * 1e3:F4} g/s Right flow = {rightFlow * 1e3:F4} g/s");
Console.WriteLine();
Console.WriteLine(
$"t = {time * 1e3:F3} ms Step {stepCount:D4}: " +
$"PA = {volA.Pressure / 1e5:F6} bar, " +
$"PB = {volB.Pressure / 1e5:F6} bar, " +
$"FlowA = {pipe.PortA.MassFlowRate * 1e3:F2} g/s");
}
}
}

54
Core/Solver.cs
View File

@@ -20,7 +20,7 @@ namespace FluidSim.Core
foreach (var v in _volumes)
v.PushStateToPort();
// 2. Apply orifice boundaries to pipes
// 2. Compute boundary fluxes (orifice model)
foreach (var conn in _connections)
{
if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
@@ -31,20 +31,20 @@ namespace FluidSim.Core
VolumeToVolume(conn);
}
// 3. Pipes simulate
// 3. Pipe simulation step
foreach (var p in _pipes)
p.Simulate();
// 4. Transfer pipe flows to connected volumes
// 4. Transfer pipe‑port data to volumes
foreach (var conn in _connections)
{
if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
Transfer(conn.PortA, conn.PortB);
TransferPipeToVolume(conn.PortA, conn.PortB);
else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
Transfer(conn.PortB, conn.PortA);
TransferPipeToVolume(conn.PortB, conn.PortA);
}
// 5. Volumes integrate
// 5. Integrate volumes
foreach (var v in _volumes)
v.Integrate();
}
@@ -61,34 +61,56 @@ namespace FluidSim.Core
double pP = isLeft ? pipe.GetLeftPressure() : pipe.GetRightPressure();
double rhoP = isLeft ? pipe.GetLeftDensity() : pipe.GetRightDensity();
double uP = 0.0;
double pV = volPort.Pressure, rhoV = volPort.Density, uV = 0.0;
double uP = isLeft ? pipe.GetCellVelocity(0)
: pipe.GetCellVelocity(pipe.GetCellCount() - 1);
double pV = volPort.Pressure;
double rhoV = volPort.Density;
double uV = 0.0; // volume has zero organized velocity
OrificeBoundary.PipeVolumeFlux(
pP, rhoP, uP,
pV, rhoV, uV,
conn, pipe.Area, isLeft,
out double massFlux, out double momFlux, out double energyFlux);
OrificeBoundary.PipeVolumeFlux(pP, rhoP, uP, pV, rhoV, uV, conn, pipe.Area,
isLeft, out double mf, out double pf, out double ef);
if (isLeft)
pipe.SetLeftBoundaryFlux(mf, pf, ef);
pipe.SetLeftBoundaryFlux(massFlux, momFlux, energyFlux);
else
pipe.SetRightBoundaryFlux(mf, pf, ef);
pipe.SetRightBoundaryFlux(massFlux, momFlux, energyFlux);
}
void VolumeToVolume(Connection conn)
{
double mdot = OrificeBoundary.MassFlow(conn.PortA.Pressure, conn.PortA.Density,
conn.PortB.Pressure, conn.PortB.Density, conn);
double mdot = OrificeBoundary.MassFlow(
conn.PortA.Pressure, conn.PortA.Density,
conn.PortB.Pressure, conn.PortB.Density, conn);
conn.PortA.MassFlowRate = -mdot;
conn.PortB.MassFlowRate = mdot;
if (mdot > 0)
conn.PortB.SpecificEnthalpy = conn.PortA.SpecificEnthalpy;
else if (mdot < 0)
conn.PortA.SpecificEnthalpy = conn.PortB.SpecificEnthalpy;
}
void Transfer(Port pipePort, Port volPort)
void TransferPipeToVolume(Port pipePort, Port volPort)
{
double mdot = pipePort.MassFlowRate;
// mdot > 0 → fluid enters pipe from volume
// mdot < 0 → fluid leaves pipe and enters volume
// Volume mass flow sign is opposite (positive into volume)
volPort.MassFlowRate = -mdot;
volPort.SpecificEnthalpy = pipePort.SpecificEnthalpy;
if (mdot < 0) // pipe → volume
{
// ★ pipePort.SpecificEnthalpy now contains TOTAL enthalpy
volPort.SpecificEnthalpy = pipePort.SpecificEnthalpy;
}
// else: fluid goes volume → pipe → volume owns its own (static) enthalpy,
// which is already correct.
}
}
}