Generating rain conditions using spray nozzles to meet standardized test specifications

Simulated rain conditions are essential for testing and validating industrial equipment, automated systems, sensors, and drones. The U.S. Department of Defense Test Method Standard MIL-STD-810H Section 506.6 specifies rainfall rates (1.7–14.0 mm/min) and droplet sizes (500–4500 μm) required to replicate real-world precipitation. This study presents methods to generate rain conditions that meet these specifications while maximizing coverage uniformity.

Various spray nozzles were evaluated to achieve the desired drop size distributions and rain rates. Key parameters such as nozzle type, operating pressure & flow rate, and nozzle-to-nozzle overlap lead to a complex balance of resulting rain characteristics including the effective rain rate, drop size distribution, and spray coverage uniformity. Pulse Width Modulation (PWM) technology enabled precise control of rain rates without altering the droplet size distribution, providing scalable test condition solutions. Using advanced imaging and analysis tools, we identified spray configurations capable of producing uniform coverage and compliant droplet size distributions across low, moderate, and high rain intensities.