Add turbocharged twin scenario and cross-platform test harness

include/FluidSim/AudioProcessing.hpp

@@ -10,21 +10,21 @@ struct Vec3 { float x{}, y{}, z{}; };
 // Flow-derivative sound source used by the C# two-stroke and pulse scenarios.
 class SoundProcessor {
 public:
-    float gain{1.0f};
+    float gain{0.005f};
     explicit SoundProcessor(int sample_rate = 44100, float listener_distance = 1.0f);
     float process(float mass_flow_out);
 private:
-    float dt_{}, scale_factor_{}, lowpass_alpha_{}, derivative_alpha_{};
-    float flow_lowpass_{}, previous_flow_{}, smooth_derivative_{};
+    float dt_{}, scale_factor_{}, previous_flow_{};
 };
 
 class RadiationSource {
 public:
-    float flow_tau{0.005f}, smooth_tau{0.020f}, gain{15.0f};
+    // Optional diagnostic filters; disabled for the linear radiation path.
+    float flow_tau{0.0f}, smooth_tau{0.0f}, gain{0.005f};
     Vec3 pipe_end{}, pipe_axis{1.0f, 0.0f, 0.0f};
     Vec3 listener{0.0f, 0.0f, 1.5f}, listener_right{1.0f, 0.0f, 0.0f};
-    float ear_spacing{0.18f}, head_shadow_cutoff{4000.0f}, speed_of_sound{343.0f};
-    float directivity_balance{0.30f}, air_absorption_exponent{0.002f}, min_air_cutoff{1500.0f};
+    float ear_spacing{0.18f}, head_shadow_cutoff{0.0f}, speed_of_sound{343.0f};
+    float directivity_balance{0.0f}, air_absorption_exponent{0.0f}, min_air_cutoff{1500.0f};
 
     explicit RadiationSource(int sample_rate = 44100);
     AudioFrame process(float mass_flow);