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orifice confirmed working

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This commit is contained in:
grillkol
2026-05-07 13:28:41 +02:00
parent 685b48b577
commit f79cf6b7eb
5 changed files with 143 additions and 150 deletions
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33
Components/Volume0D.cs
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@@ -4,23 +4,17 @@ using FluidSim.Interfaces;
namespace FluidSim.Components
{
/// <summary>
/// Zero‑dimensional control volume with arbitrary number of ports.
/// Integrates mass and energy fluxes from all ports.
/// Safeguards keep a tiny amount of gas to avoid negative states.
/// </summary>
public class Volume0D : IComponent
{
public List<Port> Ports { get; } = new List<Port>();
public double Mass { get; private set; }
public double InternalEnergy { get; private set; }
public double Mass { get; set; } // made public setter
public double InternalEnergy { get; set; } // made public setter
public double Volume { get; set; }
public double Dvdt { get; set; }
public double Gamma { get; set; } = 1.4;
public double GasConstant { get; set; } = 287.0;
// Ambient pressure used for emergency refill – default 101325 Pa
public double AmbientPressure { get; set; } = 101325.0;
// Derived quantities
@@ -42,11 +36,9 @@ namespace FluidSim.Components
InternalEnergy = (initialPressure * Volume) / (Gamma - 1.0);
}
/// <summary>Add a new port and initialise it to the volume's current state.</summary>
public Port CreatePort()
{
var port = new Port { Owner = this };
// Set the port state immediately to avoid a mismatch before the first integration
port.Pressure = Pressure;
port.Density = Density;
port.Temperature = Temperature;
@@ -56,9 +48,18 @@ namespace FluidSim.Components
}
/// <summary>
/// Integrate over dt using the MassFlowRate and SpecificEnthalpy
/// that have been set on each port during the coupling resolution phase.
/// Set the pressure to a specific value while keeping the current temperature constant.
/// Updates Mass and InternalEnergy accordingly.
/// </summary>
public void SetPressure(double pressure)
{
double V = Math.Max(Volume, 1e-12);
double currentT = Temperature; // current temperature before changes
double rho = pressure / (GasConstant * currentT);
Mass = rho * V;
InternalEnergy = pressure * V / (Gamma - 1.0);
}
public void UpdateState(double dt)
{
double totalMdot = 0.0;
@@ -67,17 +68,15 @@ namespace FluidSim.Components
foreach (var port in Ports)
{
totalMdot += port.MassFlowRate;
// mdot * h gives energy flow: positive mdot = inflow, negative = outflow
totalEdot += port.MassFlowRate * port.SpecificEnthalpy;
}
double dm = totalMdot * dt;
double dE = totalEdot * dt - Pressure * Dvdt * dt; // piston work
double dE = totalEdot * dt - Pressure * Dvdt * dt;
Mass += dm;
InternalEnergy += dE;
// Safeguards: keep at least 1 µg of gas at a small pressure
double V = Math.Max(Volume, 1e-12);
if (Mass < 1e-9)
{
@@ -89,18 +88,16 @@ namespace FluidSim.Components
InternalEnergy = AmbientPressure * V / (Gamma - 1.0);
}
// Final non‑negative clamps (should not be needed after above)
if (Mass < 0.0) Mass = 1e-9;
if (InternalEnergy < 0.0) InternalEnergy = AmbientPressure * V / (Gamma - 1.0);
// Push updated state back to all ports
double p = Pressure, rho = Density, T = Temperature, h = SpecificEnthalpy;
foreach (var port in Ports)
{
port.Pressure = p;
port.Density = rho;
port.Temperature = T;
port.SpecificEnthalpy = h; // will be overwritten by couplings for inflow, but this is the default
port.SpecificEnthalpy = h;
}
}

83
Core/OpenEndLink.cs
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@@ -3,14 +3,19 @@ using FluidSim.Components;
namespace FluidSim.Core
{
/// <summary>
/// Characteristic open‑end boundary condition after Jones (1978).
/// For all subsonic flow (outflow and inflow), the ghost state is derived
/// from the isentropic expansion to ambient pressure, using the pipe's entropy,
/// and the outgoing Riemann invariant. This avoids a density jump at flow reversal.
/// Supersonic outflow extrapolates the interior state.
/// </summary>
public class OpenEndLink
{
public Pipe1D Pipe { get; }
public bool IsLeftEnd { get; }
public double AmbientPressure { get; set; } = 101325.0;
public double Gamma { get; set; } = 1.4;
public double GasConstant { get; set; } = 287.0;
public double AmbientTemperature { get; set; } = 300.0;
public double LastMassFlowRate { get; private set; }
public double LastFaceDensity { get; private set; }
@@ -33,61 +38,63 @@ namespace FluidSim.Core
double gm1 = gamma - 1.0;
double cInt = Math.Sqrt(gamma * pInt / Math.Max(rhoInt, 1e-12));
double pAmb = AmbientPressure;
double rhoAmb = pAmb / (GasConstant * AmbientTemperature);
double aAmb = Math.Sqrt(gamma * pAmb / rhoAmb);
// Riemann invariants
double J_plus = uInt + 2.0 * cInt / gm1;
double J_minus = uInt - 2.0 * cInt / gm1;
double rhoGhost, uGhost, pGhost;
// ----- Supersonic outflow: extrapolate interior -----
bool supersonicOut = IsLeftEnd ? (uInt <= -cInt) : (uInt >= cInt);
if (supersonicOut)
// ---- Subsonic branch (used for both outflow and inflow) ----
// Isentropic expansion to ambient pressure using pipe's entropy
double s = pInt / Math.Pow(rhoInt, gamma); // entropy constant
double rhoIso = Math.Pow(pAmb / s, 1.0 / gamma);
double cIso = Math.Sqrt(gamma * pAmb / Math.Max(rhoIso, 1e-12));
double uIso = IsLeftEnd
? (J_minus + 2.0 * cIso / gm1)
: (J_plus - 2.0 * cIso / gm1);
// Check for supersonic outflow: if the isentropic velocity exceeds the speed of sound,
// the flow is supersonic and we extrapolate the interior state.
bool supersonic = IsLeftEnd
? (uInt <= -cInt) // left end: outflow is when u < -c
: (uInt >= cInt); // right end: outflow is when u > c
// Extra check: if the isentropic velocity is supersonic in the outflow direction,
// also treat as supersonic (this can happen when the interior pressure is very high).
if (!supersonic)
{
if (IsLeftEnd)
supersonic = uIso <= -cIso;
else
supersonic = uIso >= cIso;
}
if (supersonic)
{
// Supersonic outflow – extrapolate interior
rhoGhost = rhoInt;
uGhost = uInt;
pGhost = pInt;
}
else
{
// Riemann invariants
double J_plus = uInt + 2.0 * cInt / gm1;
double J_minus = uInt - 2.0 * cInt / gm1;
// Trial subsonic outflow ghost state
double s = pInt / Math.Pow(rhoInt, gamma);
double rhoOut = Math.Pow(pAmb / s, 1.0 / gamma);
double cOut = Math.Sqrt(gamma * pAmb / rhoOut);
double uOut = IsLeftEnd
? (J_minus + 2.0 * cOut / gm1)
: (J_plus - 2.0 * cOut / gm1);
bool outflowPossible = IsLeftEnd ? (uOut <= 0) : (uOut >= 0);
if (outflowPossible)
{
// Subsonic outflow
pGhost = pAmb;
rhoGhost = rhoOut;
uGhost = uOut;
}
else
{
// Subsonic inflow (ambient reservoir model)
pGhost = pAmb;
rhoGhost = rhoAmb;
uGhost = IsLeftEnd
? (J_minus + 2.0 * aAmb / gm1)
: (J_plus - 2.0 * aAmb / gm1);
}
// Subsonic flow – use the isentropic state
rhoGhost = rhoIso;
uGhost = uIso;
pGhost = pAmb;
}
// Apply ghost to pipe
if (IsLeftEnd)
Pipe.SetGhostLeft(rhoGhost, uGhost, pGhost);
else
Pipe.SetGhostRight(rhoGhost, uGhost, pGhost);
// Mass flow out of the pipe (positive = leaving)
double area = Pipe.Area;
double mdot = rhoGhost * uGhost * area;
if (IsLeftEnd) mdot = -mdot;
if (IsLeftEnd) mdot = -mdot; // left end: positive u is into pipe, so out is -u
LastMassFlowRate = mdot;
LastFaceDensity = rhoGhost;
LastFaceVelocity = uGhost;

42
Core/Solver.cs
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@@ -6,10 +6,6 @@ using FluidSim.Interfaces;
namespace FluidSim.Core
{
/// <summary>
/// Top‑level solver that owns all components and couplings,
/// orchestrates sub‑stepping, and exposes states for audio.
/// </summary>
public class Solver
{
private readonly List<IComponent> _components = new();
@@ -19,6 +15,9 @@ namespace FluidSim.Core
private double _dt;
/// <summary>CFL target for sub‑stepping (0.3‑0.8). Lower values are safer for shocks.</summary>
public double CflTarget { get; set; } = 0.8;
public void SetTimeStep(double dt) => _dt = dt;
public void AddComponent(IComponent component) => _components.Add(component);
@@ -26,57 +25,38 @@ namespace FluidSim.Core
public void AddJunction(Junction junction) => _junctions.Add(junction);
public void AddOpenEndLink(OpenEndLink link) => _openEndLinks.Add(link);
// Convenience: first pipe’s port B mass flow (often the exhaust)
public double ExhaustMassFlow
{
get
{
var pipes = _components.OfType<Pipe1D>().ToList();
if (pipes.Count > 0)
return Math.Abs(pipes[0].PortB.MassFlowRate);
return 0.0;
}
}
/// <summary>
/// Advance the whole system by one global time step.
/// </summary>
public void Step()
{
var pipes = _components.OfType<Pipe1D>().ToList();
if (pipes.Count == 0) return;
// 1. Determine sub‑step count (max CFL over all pipes)
int nSub = 1;
foreach (var p in pipes)
nSub = Math.Max(nSub, p.GetRequiredSubSteps(_dt));
nSub = Math.Max(nSub, p.GetRequiredSubSteps(_dt, CflTarget));
double dtSub = _dt / nSub;
// 2. Sub‑step loop
const int maxSubSteps = 10000;
if (nSub > maxSubSteps)
{
Console.WriteLine($"Warning: required sub‑steps {nSub} exceeds limit. Simulation stopped.");
return;
}
for (int sub = 0; sub < nSub; sub++)
{
// a) Resolve all orifice links (volume ↔ pipe)
foreach (var link in _orificeLinks)
link.Resolve(dtSub);
// b) Resolve all open‑end links (pipe → atmosphere)
foreach (var link in _openEndLinks)
link.Resolve(dtSub);
// c) Resolve all junctions (pipe ↔ pipe)
foreach (var junc in _junctions)
junc.Resolve(dtSub);
// d) Advance all pipes
foreach (var p in pipes)
p.SimulateSingleStep(dtSub);
}
// 3. Clear ghost flags
foreach (var p in pipes)
p.ClearGhostFlags();
// 4. Integrate non‑pipe components (volumes, atmosphere, etc.)
foreach (var comp in _components)
comp.UpdateState(_dt);
}

2
Program.cs
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@@ -14,7 +14,7 @@ public class Program
private static Scenario scenario;
// Speed control (existing + new throttle)
private static double desiredSpeed = 0.001;
private static double desiredSpeed = 0.01;
//private static double desiredSpeed = 1.0;
private static double currentSpeed = desiredSpeed;
private const double MinSpeed = 0.0001;

133
Scenarios/TestScenario.cs
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@@ -3,60 +3,74 @@ using SFML.Graphics;
using SFML.System;
using FluidSim.Components;
using FluidSim.Core;
using FluidSim.Utils;
namespace FluidSim.Tests
{
public class TestScenario : Scenario
{
private Solver solver;
private Volume0D volume;
private Pipe1D pipe;
private OrificeLink closedEnd; // left end – closed wall
private OpenEndLink openEndLink; // right end – atmosphere
private OrificeLink orifice; // volume → pipe left
private OpenEndLink openEnd; // pipe right → atmosphere
private SoundProcessor soundProcessor;
private OutdoorExhaustReverb reverb;
private int stepCount;
private double simTime; // elapsed simulation time (seconds)
private double pulseInterval = 0.1; // seconds between pulses
private double nextPulseTime;
// Pressure reset scheduling
private double simTime;
private double dt;
private double resetInterval = 0.2; // seconds between resets
private double nextResetTime;
private double targetPressure = 10 * Units.atm;
private double rampDuration = 0.002; // 2 ms ramp
private double rampStartTime;
private double rampStartPressure; // pressure when ramp started
private bool ramping;
public override void Initialize(int sampleRate)
{
dt = 1.0 / sampleRate;
soundProcessor = new SoundProcessor(sampleRate, 1);
soundProcessor.Gain = 10;
reverb = new OutdoorExhaustReverb(sampleRate);
soundProcessor.Gain = 2.0f; // lower gain to avoid clipping
solver = new Solver();
solver.SetTimeStep(dt);
solver.CflTarget = 0.4;
// Pipe: 2 m long, 1 cm² area, 200 cells
pipe = new Pipe1D(length: 2, area: 1e-4, cellCount: 100);
volume = new Volume0D(1e-3, targetPressure, 300.0);
solver.AddComponent(volume);
pipe = new Pipe1D(1.0, 1e-4, 200);
pipe.EnergyRelaxationRate = 10;
solver.AddComponent(pipe);
// Initially pipe at ambient conditions
pipe.SetUniformState(1.225, 0.0, 101325.0);
var volPort = volume.CreatePort();
double orificeArea = 1e-5;
orifice = new OrificeLink(volPort, pipe, isPipeLeftEnd: true,
areaProvider: () => orificeArea)
{
DischargeCoefficient = 0.62,
UseInertance = true,
EffectiveLength = 0.001
};
solver.AddOrificeLink(orifice);
// Left end: closed wall (area = 0 → reflective)
closedEnd = new OrificeLink(null, pipe, isPipeLeftEnd: true, areaProvider: () => 0.0);
solver.AddOrificeLink(closedEnd);
// Right end: open to atmosphere
openEndLink = new OpenEndLink(pipe, isLeftEnd: false)
openEnd = new OpenEndLink(pipe, isLeftEnd: false)
{
AmbientPressure = 101325.0,
Gamma = 1.4
};
solver.AddOpenEndLink(openEndLink);
solver.AddOpenEndLink(openEnd);
stepCount = 0;
simTime = 0.0;
nextPulseTime = pulseInterval; // first pulse at 100 ms
nextResetTime = resetInterval;
ramping = false;
Console.WriteLine("Pulse reflection test – closed left, open right");
Console.WriteLine("Pulse injected every 100 ms at left end (cell 0)");
Console.WriteLine("Pressure reset test with smooth ramp");
Console.WriteLine($"Volume 1L, reset to {targetPressure} Pa every {resetInterval*1000} ms, ramp {rampDuration*1000} ms");
}
public override float Process()
@@ -65,59 +79,54 @@ namespace FluidSim.Tests
stepCount++;
simTime += dt;
// ---- Inject a pressure pulse at the closed end every 100 ms ----
if (simTime >= nextPulseTime)
// ---- Smooth pressure ramp ----
if (ramping)
{
// Apply a Gaussian pulse to the first few cells
double ambientPressure = 101325.0;
double pulseAmplitude = 20 * ambientPressure; // 0.5 atm overpressure
double pulseWidth = 0.05; // m (spread over a few cells)
int n = pipe.CellCount;
double dx = 2.0 / n;
// Only modify cells within 2*pulseWidth from the left end
int maxCell = Math.Min(5, n - 1); // at most the first 5 cells
for (int i = 0; i <= maxCell; i++)
double elapsed = simTime - rampStartTime;
if (elapsed >= rampDuration)
{
double x = (i + 0.5) * dx;
double P = pulseAmplitude * Math.Exp(-x * x / (pulseWidth * pulseWidth));
double currentP = pipe.GetCellPressure(i);
double newP = P;
// Update pressure, keeping density and velocity unchanged
// We recompute total energy accordingly
double rho = pipe.GetCellDensity(i);
double u = pipe.GetCellVelocity(i);
double e = newP / ((1.4 - 1.0) * rho);
double E = rho * e + 0.5 * rho * u * u;
pipe.SetCellState(i, rho, u, newP);
// Ramp finished, set exactly to target
volume.SetPressure(targetPressure);
ramping = false;
}
else
{
double frac = elapsed / rampDuration;
double currentTarget = rampStartPressure + (targetPressure - rampStartPressure) * frac;
volume.SetPressure(currentTarget);
}
Console.WriteLine($"Pulse injected at t = {simTime:F3} s");
nextPulseTime += pulseInterval;
}
// Audio from open‑end mass flow
float sample = soundProcessor.Process(openEndLink);
// Log every 200 steps
if (stepCount % 1000 == 0)
// ---- Trigger a new reset ----
if (!ramping && simTime >= nextResetTime)
{
int leftIdx = 0;
int midIdx = pipe.CellCount / 2;
int rightIdx = pipe.CellCount - 1;
double pL = pipe.GetCellPressure(leftIdx);
double pM = pipe.GetCellPressure(midIdx);
double pR = pipe.GetCellPressure(rightIdx);
rampStartPressure = volume.Pressure; // current pressure before reset
rampStartTime = simTime;
ramping = true;
nextResetTime += resetInterval;
}
Console.WriteLine($"Step {stepCount}: P_left={pL:F1} Pa, P_mid={pM:F1} Pa, P_right={pR:F1} Pa");
// Log every 500 steps
if (stepCount % 500 == 0)
{
double volP = volume.Pressure;
double pipeL = pipe.GetCellPressure(0);
double pipeR = pipe.GetCellPressure(pipe.CellCount - 1);
double mdotOrif = orifice.LastMassFlowRate;
double mdotOpen = openEnd.LastMassFlowRate;
Console.WriteLine($"Step {stepCount}: " +
$"VolP={volP:F1} Pa, PipeL={pipeL:F1}, PipeR={pipeR:F1}, " +
$"mdot_orif={mdotOrif:E4} kg/s, mdot_open={mdotOpen:E4} kg/s");
}
if (double.IsNaN(pipe.GetCellPressure(0)))
{
Console.WriteLine("NaN detected – stopping simulation.");
Console.WriteLine("NaN detected – stopping.");
return 0f;
}
return reverb.Process(sample);
return soundProcessor.Process(openEnd);
}
public override void Draw(RenderWindow target)