Add turbocharged twin scenario and cross-platform test harness

include/FluidSim/TwoStrokeConfig.hpp

@@ -0,0 +1,38 @@
+#pragma once
+#include "FluidSim/PipeProfile.hpp"
+#include <array>
+
+namespace fluidsim::port {
+enum class TwoStrokeExhaust { Racing, Straight };
+
+// YZ125-sized baseline. Port/chamber/combustion dimensions are explicit design
+// estimates, not a measured Yamaha cylinder or factory exhaust/ignition map.
+struct TwoStrokeConfig {
+    TwoStrokeExhaust exhaust{TwoStrokeExhaust::Racing};
+    float bore{.054f}, stroke{.0545f}, rod{.110f};
+    float trapped_compression{8.2f}; // exhaust-closure volume / clearance volume
+    float transfer_duration{130}, exhaust_duration{190};
+    float transfer_width{.050f}, exhaust_width{.036f}; // summed effective window widths
+    float carburetor_diameter{.0381f};
+    float minimum_burn_seconds{.0008f};
+    // Empirical mechanical FMEP = A + B*mean_piston_speed + C*speed^2.
+    // Generic correlation estimates, not a measured YZ125 coast-down fit.
+    float friction_bar{.4f}, friction_bar_per_mps{.09f}, friction_bar_per_mps2{.0009f};
+    float exhaust_cell_length{.01f};
+    std::array<PipeSection, 6> racing_pipe{{
+        {.160f, .036f, .036f}, // header
+        {.180f, .036f, .060f}, // shallow first diffuser
+        {.190f, .060f, .105f}, // second diffuser
+        {.130f, .105f, .105f}, // belly
+        {.210f, .105f, .022f}, // convergent / baffle cone
+        {.240f, .022f, .022f}  // stinger
+    }};
+    float geometric_compression() const {
+        const float theta = (180 + exhaust_duration * .5f) * pi / 180;
+        const float radius = stroke * .5f, sine = std::sin(theta);
+        const float travel = radius * (1 - std::cos(theta)) + rod -
+                             std::sqrt(rod*rod - radius*radius*sine*sine);
+        return 1 + (trapped_compression - 1) * stroke / travel;
+    }
+};
+} // namespace fluidsim::port