Helmholtz test, sod shock tube

Components/Pipe1D.cs

@@ -21,15 +21,16 @@ namespace FluidSim.Components
         private double _dx, _dt, _gamma, _area, _diameter;
         private double[] _rho, _rhou, _E;
 
-        private double _rhoLeft, _pLeft;
+        // Volume‑coupling ghost states for boundaries A and B
-        private double _rhoRight, _pRight;
+        private double _rhoA, _pA;
-        private bool _leftBCSet, _rightBCSet;
+        private double _rhoB, _pB;
+        private bool _aBCSet, _bBCSet;
 
-        private BoundaryType _leftBCType = BoundaryType.VolumeCoupling;
+        private BoundaryType _aBCType = BoundaryType.VolumeCoupling;
-        private BoundaryType _rightBCType = BoundaryType.VolumeCoupling;
+        private BoundaryType _bBCType = BoundaryType.VolumeCoupling;
 
-        private double _leftAmbientPressure = 101325.0;
+        private double _aAmbientPressure = 101325.0;
-        private double _rightAmbientPressure = 101325.0;
+        private double _bAmbientPressure = 101325.0;
 
         private const double CflTarget = 0.8;
         private const double ReferenceSoundSpeed = 340.0;
@@ -39,8 +40,8 @@ namespace FluidSim.Components
         public double GetCellPressure(int i) => Pressure(i);
         public double GetCellVelocity(int i) => _rhou[i] / Math.Max(_rho[i], 1e-12);
 
-        public BoundaryType LeftBCType => _leftBCType;
+        public BoundaryType ABCType => _aBCType;
-        public BoundaryType RightBCType => _rightBCType;
+        public BoundaryType BBCType => _bBCType;
 
         public Pipe1D(double length, double area, int sampleRate, int forcedCellCount = 0)
         {
@@ -76,10 +77,10 @@ namespace FluidSim.Components
             PortB = new Port();
         }
 
-        public void SetLeftBoundaryType(BoundaryType type) => _leftBCType = type;
+        public void SetABoundaryType(BoundaryType type) => _aBCType = type;
-        public void SetRightBoundaryType(BoundaryType type) => _rightBCType = type;
+        public void SetBBoundaryType(BoundaryType type) => _bBCType = type;
-        public void SetLeftAmbientPressure(double p) => _leftAmbientPressure = p;
+        public void SetAAmbientPressure(double p) => _aAmbientPressure = p;
-        public void SetRightAmbientPressure(double p) => _rightAmbientPressure = p;
+        public void SetBAmbientPressure(double p) => _bAmbientPressure = p;
 
         public void SetUniformState(double rho, double u, double p)
         {
@@ -102,21 +103,21 @@ namespace FluidSim.Components
             _E[i] = rho * e + 0.5 * rho * u * u;
         }
 
-        public void SetLeftVolumeState(double rhoVol, double pVol)
+        public void SetAVolumeState(double rhoVol, double pVol)
         {
-            _rhoLeft = rhoVol;
+            _rhoA = rhoVol;
-            _pLeft = pVol;
+            _pA = pVol;
-            _leftBCSet = true;
+            _aBCSet = true;
         }
 
-        public void SetRightVolumeState(double rhoVol, double pVol)
+        public void SetBVolumeState(double rhoVol, double pVol)
         {
-            _rhoRight = rhoVol;
+            _rhoB = rhoVol;
-            _pRight = pVol;
+            _pB = pVol;
-            _rightBCSet = true;
+            _bBCSet = true;
         }
 
-        public void ClearBC() => _leftBCSet = _rightBCSet = false;
+        public void ClearBC() => _aBCSet = _bBCSet = false;
 
         public int GetRequiredSubSteps(double dtGlobal, double cflTarget = 0.8)
         {
@@ -140,105 +141,90 @@ namespace FluidSim.Components
             double[] Fp = new double[n + 1];
             double[] Fe = new double[n + 1];
 
-            // Left boundary (face 0)
+            // ---------- Boundary A (face 0, left) ----------
-            switch (_leftBCType)
+            double rhoIntA = _rho[0];
+            double uIntA = _rhou[0] / Math.Max(rhoIntA, 1e-12);
+            double pIntA = Pressure(0);
+
+            switch (_aBCType)
             {
                 case BoundaryType.VolumeCoupling:
-                    if (_leftBCSet)
+                    if (_aBCSet)
                     {
-                        HLLCFlux(_rhoLeft, 0.0, _pLeft,
+                        HLLCFlux(_rhoA, 0.0, _pA,
-                                 _rho[0], _rhou[0] / Math.Max(_rho[0], 1e-12), Pressure(0),
+                                 rhoIntA, uIntA, pIntA,
                                  out Fm[0], out Fp[0], out Fe[0]);
                     }
                     else
                     {
-                        Fm[0] = 0; Fp[0] = Pressure(0); Fe[0] = 0;
+                        Fm[0] = 0; Fp[0] = pIntA; Fe[0] = 0;
                     }
                     break;
 
                 case BoundaryType.OpenEnd:
-                    {
+                    OpenEndFluxA(rhoIntA, uIntA, pIntA, _aAmbientPressure,
-                        double rhoR = _rho[0];
-                        double uR = _rhou[0] / Math.Max(rhoR, 1e-12);
-                        double pR = Pressure(0);
-                        HLLCFlux(rhoR, uR, _leftAmbientPressure,
-                                 rhoR, uR, pR,
                                  out Fm[0], out Fp[0], out Fe[0]);
-                    }
                     break;
 
                 case BoundaryType.ClosedEnd:
-                    {
+                    ClosedEndFlux(rhoIntA, uIntA, pIntA, isRightBoundary: false,
-                        double rhoR = _rho[0];
+                                  out Fm[0], out Fp[0], out Fe[0]);
-                        double uR = _rhou[0] / Math.Max(rhoR, 1e-12);
-                        double pR = Pressure(0);
-                        HLLCFlux(rhoR, -uR, pR,
-                                 rhoR, uR, pR,
-                                 out Fm[0], out Fp[0], out Fe[0]);
-                    }
                     break;
             }
 
-            // Internal faces
+            // ---------- Internal faces ----------
             for (int i = 0; i < n - 1; i++)
             {
-                double uL = _rhou[i] / Math.Max(_rho[i], 1e-12);
+                double rhoL = _rho[i];
-                double uR = _rhou[i + 1] / Math.Max(_rho[i + 1], 1e-12);
+                double uL = _rhou[i] / Math.Max(rhoL, 1e-12);
-                HLLCFlux(_rho[i], uL, Pressure(i),
+                double pL = Pressure(i);
-                         _rho[i + 1], uR, Pressure(i + 1),
+
+                double rhoR = _rho[i + 1];
+                double uR = _rhou[i + 1] / Math.Max(rhoR, 1e-12);
+                double pR = Pressure(i + 1);
+
+                HLLCFlux(rhoL, uL, pL, rhoR, uR, pR,
                          out Fm[i + 1], out Fp[i + 1], out Fe[i + 1]);
             }
 
-            // Right boundary (face n)
+            // ---------- Boundary B (face n, right) ----------
-            switch (_rightBCType)
+            double rhoIntB = _rho[n - 1];
+            double uIntB = _rhou[n - 1] / Math.Max(rhoIntB, 1e-12);
+            double pIntB = Pressure(n - 1);
+
+            switch (_bBCType)
             {
                 case BoundaryType.VolumeCoupling:
-                    if (_rightBCSet)
+                    if (_bBCSet)
                     {
-                        double rhoL = _rho[n - 1];
+                        HLLCFlux(rhoIntB, uIntB, pIntB,
-                        double uL = _rhou[n - 1] / Math.Max(rhoL, 1e-12);
+                                 _rhoB, 0.0, _pB,
-                        double pL = Pressure(n - 1);
-                        HLLCFlux(rhoL, uL, pL,
-                                 _rhoRight, 0.0, _pRight,
                                  out Fm[n], out Fp[n], out Fe[n]);
                     }
                     else
                     {
-                        Fm[n] = 0; Fp[n] = Pressure(n - 1); Fe[n] = 0;
+                        Fm[n] = 0; Fp[n] = pIntB; Fe[n] = 0;
                     }
                     break;
 
                 case BoundaryType.OpenEnd:
-                    {
+                    OpenEndFluxB(rhoIntB, uIntB, pIntB, _bAmbientPressure,
-                        double rhoL = _rho[n - 1];
-                        double uL = _rhou[n - 1] / Math.Max(rhoL, 1e-12);
-                        double pL = Pressure(n - 1);
-                        HLLCFlux(rhoL, uL, pL,
-                                 rhoL, uL, _rightAmbientPressure,
                                  out Fm[n], out Fp[n], out Fe[n]);
-                    }
                     break;
 
                 case BoundaryType.ClosedEnd:
-                    {
+                    ClosedEndFlux(rhoIntB, uIntB, pIntB, isRightBoundary: true,
-                        double rhoL = _rho[n - 1];
+                                  out Fm[n], out Fp[n], out Fe[n]);
-                        double uL = _rhou[n - 1] / Math.Max(rhoL, 1e-12);
-                        double pL = Pressure(n - 1);
-                        HLLCFlux(rhoL, uL, pL,
-                                 rhoL, -uL, pL,
-                                 out Fm[n], out Fp[n], out Fe[n]);
-                    }
                     break;
             }
 
             // ---- Cell update with linear laminar damping ----
             double radius = _diameter / 2.0;
-            double mu_air = 1.8e-5;                       // dynamic viscosity of air (Pa·s)
+            double mu_air = 1.8e-5;
             double laminarCoeff = DampingMultiplier * 8.0 * mu_air / (radius * radius);
 
             for (int i = 0; i < n; i++)
             {
-                // Flux divergence
                 double dM = (Fm[i + 1] - Fm[i]) / _dx;
                 double dP = (Fp[i + 1] - Fp[i]) / _dx;
                 double dE = (Fe[i + 1] - Fe[i]) / _dx;
@@ -247,14 +233,11 @@ namespace FluidSim.Components
                 _rhou[i] -= dtSub * dP;
                 _E[i] -= dtSub * dE;
 
-                // Laminar viscous damping on momentum (implicit exponential decay)
                 double rho = Math.Max(_rho[i], 1e-12);
-                double dampingRate = laminarCoeff / rho;   // 1/s
+                double dampingRate = laminarCoeff / rho;
                 double dampingFactor = Math.Exp(-dampingRate * dtSub);
                 _rhou[i] *= dampingFactor;
-                // Note: total energy _E[i] is unchanged – kinetic energy loss becomes internal heat
 
-                // Physical bounds
                 if (_rho[i] < 1e-12) _rho[i] = 1e-12;
                 double kinetic = 0.5 * _rhou[i] * _rhou[i] / _rho[i];
                 double pMin = 100.0;
@@ -262,28 +245,29 @@ namespace FluidSim.Components
                 if (_E[i] < eMin) _E[i] = eMin;
             }
 
-            // Port quantities (only meaningful for volume‑coupled ends)
+            // ---------- Port quantities ----------
-            double mdotA_sub = _leftBCType == BoundaryType.VolumeCoupling && _leftBCSet ? Fm[0] * _area : 0.0;
+            double mdotA_sub = _aBCType == BoundaryType.VolumeCoupling && _aBCSet ? Fm[0] * _area : 0.0;
-            double mdotB_sub = _rightBCType == BoundaryType.VolumeCoupling && _rightBCSet ? -Fm[n] * _area : 0.0;
+            double mdotB_sub = _bBCType == BoundaryType.VolumeCoupling && _bBCSet ? -Fm[n] * _area : 0.0;
 
             PortA.MassFlowRate = mdotA_sub;
             PortB.MassFlowRate = mdotB_sub;
-            PortA.Pressure = Pressure(0);
+            PortA.Pressure = pIntA;
-            PortB.Pressure = Pressure(_n - 1);
+            PortB.Pressure = pIntB;
             PortA.Density = _rho[0];
-            PortB.Density = _rho[_n - 1];
+            PortB.Density = _rho[n - 1];
 
-            if (_leftBCType == BoundaryType.VolumeCoupling && _leftBCSet)
+            // Corrected enthalpy for both directions
+            if (_aBCType == BoundaryType.VolumeCoupling && _aBCSet)
             {
                 PortA.SpecificEnthalpy = mdotA_sub < 0
                     ? GetCellTotalSpecificEnthalpy(0)
-                    : 0.0;
+                    : (_gamma / (_gamma - 1.0)) * _pA / Math.Max(_rhoA, 1e-12);
             }
-            if (_rightBCType == BoundaryType.VolumeCoupling && _rightBCSet)
+            if (_bBCType == BoundaryType.VolumeCoupling && _bBCSet)
             {
                 PortB.SpecificEnthalpy = mdotB_sub < 0
                     ? GetCellTotalSpecificEnthalpy(_n - 1)
-                    : 0.0;
+                    : (_gamma / (_gamma - 1.0)) * _pB / Math.Max(_rhoB, 1e-12);
             }
         }
 
@@ -299,6 +283,98 @@ namespace FluidSim.Components
         private double Pressure(int i) =>
             (_gamma - 1.0) * (_E[i] - 0.5 * _rhou[i] * _rhou[i] / Math.Max(_rho[i], 1e-12));
 
+        // ========== Characteristic‑based Open End ==========
+        private void OpenEndFluxA(double rhoInt, double uInt, double pInt, double pAmb,
+                                  out double fm, out double fp, out double fe)
+        {
+            double cInt = Math.Sqrt(_gamma * pInt / Math.Max(rhoInt, 1e-12));
+
+            // Subsonic inflow (uInt ≤ 0, so flow inside pipe ←)
+            if (uInt <= -cInt)   // supersonic inflow – use interior state as ghost
+            {
+                fm = rhoInt * uInt;
+                fp = rhoInt * uInt * uInt + pInt;
+                fe = (rhoInt * (pInt / ((_gamma - 1) * rhoInt) + 0.5 * uInt * uInt) + pInt) * uInt;
+                return;
+            }
+            else if (uInt <= 0)   // subsonic inflow
+            {
+                // Reservoir condition: p = pAmb, T = 300K, u = 0
+                double T0 = 300.0;
+                double R = 287.0;
+                double rhoGhost = pAmb / (R * T0);
+                HLLCFlux(rhoGhost, 0.0, pAmb, rhoInt, uInt, pInt, out fm, out fp, out fe);
+                return;
+            }
+            else   // subsonic outflow (uInt > 0)
+            {
+                // Ghost pressure forced to pAmb
+                double s = pInt / Math.Pow(rhoInt, _gamma);
+                double rhoGhost = Math.Pow(pAmb / s, 1.0 / _gamma);
+                double cGhost = Math.Sqrt(_gamma * pAmb / rhoGhost);
+
+                // Outgoing Riemann invariant J⁻ = uInt - 2*cInt/(γ-1) (for left boundary)
+                double J_minus = uInt - 2.0 * cInt / (_gamma - 1.0);
+                double uGhost = J_minus + 2.0 * cGhost / (_gamma - 1.0);
+
+                // Prevent spurious inflow by clipping to zero
+                if (uGhost < 0) uGhost = 0;
+
+                HLLCFlux(rhoGhost, uGhost, pAmb, rhoInt, uInt, pInt, out fm, out fp, out fe);
+            }
+        }
+
+        private void OpenEndFluxB(double rhoInt, double uInt, double pInt, double pAmb,
+                                  out double fm, out double fp, out double fe)
+        {
+            double cInt = Math.Sqrt(_gamma * pInt / Math.Max(rhoInt, 1e-12));
+
+            if (uInt >= cInt)   // supersonic outflow (extrapolation)
+            {
+                fm = rhoInt * uInt;
+                fp = rhoInt * uInt * uInt + pInt;
+                fe = (rhoInt * (pInt / ((_gamma - 1) * rhoInt) + 0.5 * uInt * uInt) + pInt) * uInt;
+                return;
+            }
+            else if (uInt >= 0)   // subsonic outflow
+            {
+                double s = pInt / Math.Pow(rhoInt, _gamma);
+                double rhoGhost = Math.Pow(pAmb / s, 1.0 / _gamma);
+                double cGhost = Math.Sqrt(_gamma * pAmb / rhoGhost);
+
+                // Outgoing Riemann invariant J⁺ = uInt + 2*cInt/(γ-1) (for right boundary)
+                double J_plus = uInt + 2.0 * cInt / (_gamma - 1.0);
+                double uGhost = J_plus - 2.0 * cGhost / (_gamma - 1.0);
+
+                // Clip to zero to prevent inflow
+                if (uGhost > 0) uGhost = 0;
+
+                HLLCFlux(rhoInt, uInt, pInt, rhoGhost, uGhost, pAmb, out fm, out fp, out fe);
+            }
+            else   // subsonic inflow
+            {
+                double T0 = 300.0;
+                double R = 287.0;
+                double rhoGhost = pAmb / (R * T0);
+                HLLCFlux(rhoInt, uInt, pInt, rhoGhost, 0.0, pAmb, out fm, out fp, out fe);
+            }
+        }
+
+        // ========== Closed end (mirror) ==========
+        private void ClosedEndFlux(double rhoInt, double uInt, double pInt, bool isRightBoundary,
+                                   out double fm, out double fp, out double fe)
+        {
+            double rhoGhost = rhoInt;
+            double pGhost = pInt;
+            double uGhost = -uInt;   // mirror velocity
+
+            if (isRightBoundary)
+                HLLCFlux(rhoInt, uInt, pInt, rhoGhost, uGhost, pGhost, out fm, out fp, out fe);
+            else
+                HLLCFlux(rhoGhost, uGhost, pGhost, rhoInt, uInt, pInt, out fm, out fp, out fe);
+        }
+
+        // ========== Standard HLLC flux ==========
         private void HLLCFlux(double rL, double uL, double pL,
                               double rR, double uR, double pR,
                               out double fm, out double fp, out double fe)

Core/Solver.cs

@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using FluidSim.Components;
 using FluidSim.Interfaces;
 
@@ -10,93 +11,90 @@ namespace FluidSim.Core
         private readonly List<Pipe1D> _pipes = new();
         private readonly List<Connection> _connections = new();
 
-        private double _dt;   // global time step
+        private double _dt;
 
         public void AddVolume(Volume0D v) => _volumes.Add(v);
         public void AddPipe(Pipe1D p) => _pipes.Add(p);
         public void AddConnection(Connection c) => _connections.Add(c);
-
-        /// <summary>Set the global time step (called from Simulation).</summary>
         public void SetTimeStep(double dt) => _dt = dt;
 
         /// <summary>
-        /// Convenient method to set the boundary type of a pipe end.
+        /// Set boundary type for a pipe end. isA = true for port A (left), false for port B (right).
         /// </summary>
-        public void SetPipeBoundary(Pipe1D pipe, bool isLeft, BoundaryType type, double ambientPressure = 101325.0)
+        public void SetPipeBoundary(Pipe1D pipe, bool isA, BoundaryType type, double ambientPressure = 101325.0)
         {
-            if (isLeft)
+            if (isA)
             {
-                pipe.SetLeftBoundaryType(type);
+                pipe.SetABoundaryType(type);
                 if (type == BoundaryType.OpenEnd)
-                    pipe.SetLeftAmbientPressure(ambientPressure);
+                    pipe.SetAAmbientPressure(ambientPressure);
             }
             else
             {
-                pipe.SetRightBoundaryType(type);
+                pipe.SetBBoundaryType(type);
                 if (type == BoundaryType.OpenEnd)
-                    pipe.SetRightAmbientPressure(ambientPressure);
+                    pipe.SetBAmbientPressure(ambientPressure);
             }
         }
 
         public float Step()
         {
-            // 1. Volumes publish state to ports (only needed if any volume exists)
+            // 1. Volumes publish state
             foreach (var v in _volumes)
                 v.PushStateToPort();
 
-            // 2. Set initial pipe boundary conditions ONLY for volume‑coupled ends
+            // 2. Set volume BCs for volume‑coupled ends
             foreach (var conn in _connections)
             {
                 if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
                 {
                     var pipe = GetPipe(conn.PortA);
-                    bool isLeft = pipe.PortA == conn.PortA;
+                    bool isA = pipe.PortA == conn.PortA;
-                    BoundaryType bc = isLeft ? pipe.LeftBCType : pipe.RightBCType;
+                    if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
-                    if (bc == BoundaryType.VolumeCoupling)
+                        (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
                         SetVolumeBC(conn.PortA, conn.PortB);
                 }
                 else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
                 {
                     var pipe = GetPipe(conn.PortB);
-                    bool isLeft = pipe.PortB == conn.PortB;
+                    bool isA = pipe.PortB == conn.PortB;
-                    BoundaryType bc = isLeft ? pipe.LeftBCType : pipe.RightBCType;
+                    if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
-                    if (bc == BoundaryType.VolumeCoupling)
+                        (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
                         SetVolumeBC(conn.PortB, conn.PortA);
                 }
             }
 
-            // 3. Determine number of sub‑steps
+            // 3. Sub‑steps
             int nSub = 1;
             foreach (var p in _pipes)
                 nSub = Math.Max(nSub, p.GetRequiredSubSteps(_dt));
             double dtSub = _dt / nSub;
 
-            // 4. Sub‑step loop
             for (int sub = 0; sub < nSub; sub++)
             {
                 foreach (var p in _pipes)
                     p.SimulateSingleStep(dtSub);
 
-                // Transfer flows only for volume‑coupled connections
                 foreach (var conn in _connections)
                 {
                     if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
                     {
                         var pipe = GetPipe(conn.PortA);
-                        bool isLeft = pipe.PortA == conn.PortA;
+                        bool isA = pipe.PortA == conn.PortA;
-                        if (pipe.LeftBCType == BoundaryType.VolumeCoupling || pipe.RightBCType == BoundaryType.VolumeCoupling)
+                        if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
+                            (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
                             TransferAndIntegrate(conn.PortA, conn.PortB, dtSub);
                     }
                     else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
                     {
                         var pipe = GetPipe(conn.PortB);
-                        bool isLeft = pipe.PortB == conn.PortB;
+                        bool isA = pipe.PortB == conn.PortB;
-                        if (pipe.LeftBCType == BoundaryType.VolumeCoupling || pipe.RightBCType == BoundaryType.VolumeCoupling)
+                        if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
+                            (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
                             TransferAndIntegrate(conn.PortB, conn.PortA, dtSub);
                     }
                 }
 
-                // Update BCs for volume‑coupled ends between sub‑steps
                 if (sub < nSub - 1)
                 {
                     foreach (var v in _volumes)
@@ -107,24 +105,24 @@ namespace FluidSim.Core
                         if (IsPipePort(conn.PortA) && IsVolumePort(conn.PortB))
                         {
                             var pipe = GetPipe(conn.PortA);
-                            bool isLeft = pipe.PortA == conn.PortA;
+                            bool isA = pipe.PortA == conn.PortA;
-                            if ((isLeft && pipe.LeftBCType == BoundaryType.VolumeCoupling) ||
+                            if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
-                                (!isLeft && pipe.RightBCType == BoundaryType.VolumeCoupling))
+                                (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
                                 SetVolumeBC(conn.PortA, conn.PortB);
                         }
                         else if (IsVolumePort(conn.PortA) && IsPipePort(conn.PortB))
                         {
                             var pipe = GetPipe(conn.PortB);
-                            bool isLeft = pipe.PortB == conn.PortB;
+                            bool isA = pipe.PortB == conn.PortB;
-                            if ((isLeft && pipe.LeftBCType == BoundaryType.VolumeCoupling) ||
+                            if ((isA && pipe.ABCType == BoundaryType.VolumeCoupling) ||
-                                (!isLeft && pipe.RightBCType == BoundaryType.VolumeCoupling))
+                                (!isA && pipe.BBCType == BoundaryType.VolumeCoupling))
                                 SetVolumeBC(conn.PortB, conn.PortA);
                         }
                     }
                 }
             }
 
-            // 5. Audio samples from SoundConnections (if any)
+            // 5. Audio samples (none for now, but placeholder)
             var audioSamples = new List<float>();
             foreach (var conn in _connections)
             {
@@ -132,7 +130,7 @@ namespace FluidSim.Core
                     audioSamples.Add(sc.GetAudioSample());
             }
 
-            // 6. Clear volume BC flags
+            // 6. Clear BC flags
             foreach (var p in _pipes)
                 p.ClearBC();
 
@@ -148,11 +146,11 @@ namespace FluidSim.Core
         {
             var pipe = GetPipe(pipePort);
             if (pipe == null) return;
-            bool isLeft = pipe.PortA == pipePort;
+            bool isA = pipe.PortA == pipePort;
-            if (isLeft)
+            if (isA)
-                pipe.SetLeftVolumeState(volPort.Density, volPort.Pressure);
+                pipe.SetAVolumeState(volPort.Density, volPort.Pressure);
             else
-                pipe.SetRightVolumeState(volPort.Density, volPort.Pressure);
+                pipe.SetBVolumeState(volPort.Density, volPort.Pressure);
         }
 
         private void TransferAndIntegrate(Port pipePort, Port volPort, double dtSub)
@@ -164,7 +162,7 @@ namespace FluidSim.Core
             {
                 volPort.SpecificEnthalpy = pipePort.SpecificEnthalpy;
             }
-            // else: volume’s own enthalpy (set by PushStateToPort) is used
+            // else volume’s own enthalpy (from PushStateToPort) is used
 
             GetVolume(volPort)?.Integrate(dtSub);
         }

Program.cs

@@ -13,7 +13,8 @@ public class Program
     private static Scenario scenario;
 
     // Speed control
-    private static double desiredSpeed = 1.0;
+    //private static double desiredSpeed = 1.0;
+    private static double desiredSpeed = 0.0001;
     private static double currentSpeed = desiredSpeed;
     private const double MinSpeed = 0.0001;
     private const double MaxSpeed = 1.0;
@@ -38,7 +39,10 @@ public class Program
         soundEngine.Volume = 70;
         soundEngine.Start();
 
-        scenario = new PipeResonatorScenario();
+        //scenario = new PipeResonatorScenario();
+        //scenario = new HelmholtzResonatorScenario();
+        scenario = new SodShockTubeScenario();
+
         scenario.Initialize(SampleRate);
 
         var stopwatch = Stopwatch.StartNew();

Scenarios/HelmholtzResonatorScenario.cs

@@ -0,0 +1,133 @@
+using System;
+using FluidSim.Components;
+using FluidSim.Interfaces;
+using FluidSim.Utils;
+using SFML.Graphics;
+using SFML.System;
+
+namespace FluidSim.Core
+{
+    public class HelmholtzResonatorScenario : Scenario
+    {
+        private Solver solver;
+        private Volume0D cavity;
+        private Pipe1D neck;
+        private Connection coupling;
+        private int stepCount;
+        private double time;
+        private double dt;
+        private double ambientPressure = 1.0 * Units.atm;
+
+        public override void Initialize(int sampleRate)
+        {
+            dt = 1.0 / sampleRate;
+
+            // 1‑litre cavity, 10% over‑pressure
+            double cavityVolume = 1e-3;
+            double initialCavityPressure = 1.1 * ambientPressure;
+            cavity = new Volume0D(cavityVolume, initialCavityPressure, 300.0, sampleRate)
+            {
+                Gamma = 1.4,
+                GasConstant = 287.0
+            };
+
+            // Neck: length 10 cm, radius 1 cm
+            double neckLength = 0.1;
+            double neckRadius = 0.01;
+            double neckArea = Math.PI * neckRadius * neckRadius;
+            neck = new Pipe1D(neckLength, neckArea, sampleRate, forcedCellCount: 40);
+            neck.SetUniformState(1.225, 0.0, ambientPressure);
+
+            coupling = new Connection(neck.PortA, cavity.Port)
+            {
+                Area = neckArea,
+                DischargeCoefficient = 0.62,
+                Gamma = 1.4
+            };
+
+            solver = new Solver();
+            solver.SetTimeStep(dt);
+            solver.AddVolume(cavity);
+            solver.AddPipe(neck);
+            solver.AddConnection(coupling);
+
+            // Port A (left) = volume coupling, Port B (right) = open end
+            solver.SetPipeBoundary(neck, isA: true, BoundaryType.VolumeCoupling);
+            solver.SetPipeBoundary(neck, isA: false, BoundaryType.OpenEnd, ambientPressure);
+        }
+
+        public override float Process()
+        {
+            float sample = solver.Step();
+            time += dt;
+            stepCount++;
+
+            double pOpen = neck.GetCellPressure(neck.GetCellCount() - 1);
+            float audio = (float)((pOpen - ambientPressure) / ambientPressure);
+
+            if (stepCount % 20 == 0)
+            {
+                double pCav = cavity.Pressure;
+                double mdotA = neck.PortA.MassFlowRate;   // positive = into pipe (leaving cavity)
+                Console.WriteLine(
+                    $"t={time * 1e3:F2} ms step={stepCount} " +
+                    $"P_cav={pCav:F1} Pa, P_open={pOpen:F1} Pa, " +
+                    $"mdot_A={mdotA * 1e3:F4} g/s, audio={audio:F4}");
+            }
+
+            return audio;
+        }
+
+        public override void Draw(RenderWindow target)
+        {
+            float winW = target.GetView().Size.X;
+            float winH = target.GetView().Size.Y;
+            float centerY = winH / 2f;
+
+            // Cavity rectangle
+            float cavityWidth = 120f;
+            float cavityHeight = 180f;
+            var cavityRect = new RectangleShape(new Vector2f(cavityWidth, cavityHeight));
+            cavityRect.Position = new Vector2f(40f, centerY - cavityHeight / 2f);
+            cavityRect.FillColor = PressureColor(cavity.Pressure);
+            target.Draw(cavityRect);
+
+            // Neck drawn as tapered pipe
+            int n = neck.GetCellCount();
+            float neckStartX = 40f + cavityWidth + 10f;
+            float neckEndX = winW - 60f;
+            float neckLenPx = neckEndX - neckStartX;
+            float dx = neckLenPx / (n - 1);
+            float baseRadius = 20f;
+
+            Vertex[] vertices = new Vertex[n * 2];
+            for (int i = 0; i < n; i++)
+            {
+                float x = neckStartX + i * dx;
+                double p = neck.GetCellPressure(i);
+                float r = baseRadius * (float)(0.5 + 0.5 * Math.Tanh((p - ambientPressure) / (ambientPressure * 0.2)));
+                if (r < 4f) r = 4f;
+                Color col = PressureColor(p);
+                vertices[i * 2] = new Vertex(new Vector2f(x, centerY - r), col);
+                vertices[i * 2 + 1] = new Vertex(new Vector2f(x, centerY + r), col);
+            }
+            target.Draw(vertices, PrimitiveType.TriangleStrip);
+
+            // Open end indicator
+            var arrow = new CircleShape(8f);
+            arrow.Position = new Vector2f(neckEndX - 4f, centerY - 4f);
+            arrow.FillColor = Color.White;
+            target.Draw(arrow);
+        }
+
+        private Color PressureColor(double pressure)
+        {
+            double range = ambientPressure * 0.1;
+            double t = Math.Clamp((pressure - ambientPressure) / range, -1.0, 1.0);
+            byte r = (byte)(t > 0 ? 255 * t : 0);
+            byte b = (byte)(t < 0 ? -255 * t : 0);
+            byte g = (byte)(255 * (1 - Math.Abs(t)));
+            return new Color(r, g, b);
+        }
+    }
+}

Scenarios/PipeResonatorScenario.cs

@@ -21,7 +21,7 @@ namespace FluidSim.Core
         {
             dt = 1.0 / sampleRate;
 
-            double length = 0.5;
+            double length = 2;
             double radius = 50 * Units.mm;
             double area = Units.AreaFromDiameter(radius);
 
@@ -31,8 +31,9 @@ namespace FluidSim.Core
             solver = new Solver();
             solver.SetTimeStep(dt);
             solver.AddPipe(pipe);
-            solver.SetPipeBoundary(pipe, isLeft: true, BoundaryType.OpenEnd, ambientPressure);
+            // Open end at port A (left), closed end at port B (right)
-            solver.SetPipeBoundary(pipe, isLeft: false, BoundaryType.ClosedEnd);
+            solver.SetPipeBoundary(pipe, isA: true, BoundaryType.OpenEnd, ambientPressure);
+            solver.SetPipeBoundary(pipe, isA: false, BoundaryType.ClosedEnd);
 
             // Initial pressure pulse
             int pulseCells = 5;

Scenarios/SodShockTubeScenario.cs

@@ -0,0 +1,158 @@
+using System;
+using FluidSim.Components;
+using FluidSim.Utils;
+using SFML.Graphics;
+using SFML.System;
+
+namespace FluidSim.Core
+{
+    public class SodShockTubeScenario : Scenario
+    {
+        private Solver solver;
+        private Pipe1D pipe;
+        private int stepCount;
+        private double time;
+        private double dt;
+        private double ambientPressure = 1.0 * Units.atm;
+        private const double GasConstant = 287.0;
+
+        public override void Initialize(int sampleRate)
+        {
+            dt = 1.0 / sampleRate;
+            double length = 1.0;
+            double area = 1.0;
+            int nCells = 200;
+
+            pipe = new Pipe1D(length, area, sampleRate, forcedCellCount: nCells);
+            pipe.SetUniformState(0.125, 0.0, 0.1 * ambientPressure);  // right state
+
+            // Left half high pressure
+            for (int i = 0; i < nCells / 2; i++)
+                pipe.SetCellState(i, 1.0, 0.0, ambientPressure);
+
+            solver = new Solver();
+            solver.SetTimeStep(dt);
+            solver.AddPipe(pipe);
+            solver.SetPipeBoundary(pipe, isA: true, BoundaryType.ClosedEnd);
+            solver.SetPipeBoundary(pipe, isA: false, BoundaryType.ClosedEnd);
+        }
+
+        public override float Process()
+        {
+            float sample = solver.Step();
+            time += dt;
+            stepCount++;
+
+            double pMid = pipe.GetPressureAtFraction(0.5);
+            float audio = (float)((pMid - ambientPressure) / ambientPressure);
+
+            bool log = true;
+
+            if (log)
+            {
+                int n = pipe.GetCellCount();
+                Console.WriteLine($"step {stepCount}:");
+                Console.WriteLine("i    rho (kg/m³)   p (Pa)       T (K)     u (m/s)");
+                for (int i = 0; i < n; i++)
+                {
+                    if (i % 10 == 0)
+                    {
+                        double rho = pipe.GetCellDensity(i);
+                        double p = pipe.GetCellPressure(i);
+                        double u = pipe.GetCellVelocity(i);
+                        double T = p / (rho * GasConstant);   // GasConstant = 287.0
+                        Console.WriteLine($"{i,-4} {rho,10:F4}   {p,10:F1}   {T,8:F2}   {u,10:F4}");
+                    }
+                }
+                Console.WriteLine();
+            }
+
+            return audio;
+        }
+
+        public override void Draw(RenderWindow target)
+        {
+            float winW = target.GetView().Size.X;
+            float winH = target.GetView().Size.Y;
+            float centerY = winH / 2f;
+            float margin = 40f;
+            float pipeStartX = margin;
+            float pipeEndX = winW - margin;
+            float pipeLenPx = pipeEndX - pipeStartX;
+            int n = pipe.GetCellCount();
+            float dx = pipeLenPx / (n - 1);
+            float baseRadius = 60f;
+
+            Vertex[] vertices = new Vertex[n * 2];
+            for (int i = 0; i < n; i++)
+            {
+                float x = pipeStartX + i * dx;
+
+                double p = pipe.GetCellPressure(i);
+                double rho = pipe.GetCellDensity(i);
+                double T = p / (rho * GasConstant);           // temperature in Kelvin
+
+                // Radius from pressure (exaggerated deviation)
+                float r = baseRadius * (float)(p / ambientPressure * 2);
+                if (r < 4f) r = 4f;
+
+                // Colour from temperature
+                Color col = TemperatureColor(T);
+
+                vertices[i * 2] = new Vertex(new Vector2f(x, centerY - r), col);
+                vertices[i * 2 + 1] = new Vertex(new Vector2f(x, centerY + r), col);
+            }
+            target.Draw(vertices, PrimitiveType.TriangleStrip);
+
+            // Diaphragm marker (faint white line at initial interface)
+            float diaphragmX = pipeStartX + (n / 2) * dx;
+            var line = new RectangleShape(new Vector2f(2f, winH * 0.5f));
+            line.Position = new Vector2f(diaphragmX - 1f, centerY - winH * 0.25f);
+            line.FillColor = new Color(255, 255, 255, 80);
+            target.Draw(line);
+        }
+
+        /// <summary>
+        /// Custom temperature‑to‑hue mapping that matches the given Sod‑tube hue values:
+        ///   250 K → 176, 300 K → 122, 350 K → 120?, 450 K → 71.
+        /// Interpolates piecewise linearly, clamping outside [250,450].
+        /// </summary>
+        private Color TemperatureColor(double T)
+        {
+            // 1. Map temperature to hue (0–360)
+            double[] Tknots = { 250, 282, 353, 450 };
+            double[] Hknots = { 176, 179, 122, 71 };
+            double hue;
+            if (T <= Tknots[0]) hue = Hknots[0];
+            else if (T >= Tknots[^1]) hue = Hknots[^1];
+            else
+            {
+                int i = 0;
+                while (i < Tknots.Length - 1 && T > Tknots[i + 1]) i++;
+                double frac = (T - Tknots[i]) / (Tknots[i + 1] - Tknots[i]);
+                hue = Hknots[i] + frac * (Hknots[i + 1] - Hknots[i]);
+            }
+
+            // 2. Convert hue to RGB (S = 1, V = 1)
+            double h = hue / 60.0;
+            int sector = (int)Math.Floor(h);
+            double f = h - sector;
+            byte p = 0;
+            byte q = (byte)(255 * (1 - f));
+            byte tByte = (byte)(255 * f);
+            byte v = 255;
+
+            byte r, g, b;
+            switch (sector % 6)
+            {
+                case 0: r = v; g = tByte; b = p; break;
+                case 1: r = q; g = v; b = p; break;
+                case 2: r = p; g = v; b = tByte; break;
+                case 3: r = p; g = q; b = v; break;
+                case 4: r = tByte; g = p; b = v; break;
+                default: r = v; g = p; b = q; break;
+            }
+            return new Color(r, g, b);
+        }
+    }
+}