Heat flux as a key to predicting optical turbulence: experimental validation of a scaling constant in Rayleigh-Bénard turbulence.

Optical turbulence caused by refractive index fluctuations poses a major challenge for imaging, free-space communication, and directed-energy systems. Rayleigh-Bénard (RB) convection offers a controlled laboratory analog for studying buoyancy-driven turbulence and its optical effects. Building on theoretical predictions that link turbulence strength to heat flux, we experimentally determine the scaling constant γ by simultaneously measuring the refractive index structure constant (Cn2) and heat flux in an RB environment. Using a variable turbulence generator (VTG), we validate RB conditions through Nusselt-Rayleigh scaling and direct numerical simulations (DNS). Three independent optical diagnostics were employed to estimate Cn2 (scintillation, beam wander, and long-term beam spot size), while embedded sensors captured heat flux. This scaling constant validation is confined to the experimental conditions described. Results confirm the predicted Cn2∝Q4/3 relationship, with γ=8.79±0.61 closely matching simulations (8.65). This strong agreement demonstrates the robustness of the heat-flux-based scaling relationship and establishes RB systems as effective testbeds for turbulence characterization. These findings provide a practical framework for predicting optical performance in complex environments and advancing turbulence mitigation strategies.