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Road accidents caused by heavy rain have become a frightening issue in recent years requiring investigation. In this regard, an aerodynamic comparative and experimental rain study is carried out to observe the flow phenomena change around a generic ground vehicle (Ahmed Body at a scale) and the utility truck. In this paper, a Discrete Phase Model (DPM) based computational methodology is used to estimate the effect of rain on aerodynamic performance. First, an experimental rain study of the Ahmed body at a scale that is representative of a car or light truck was conducted at the Wall of Wind (WOW) large-scale testing facility using force measurement equipment. In addition, the experiment allowed drag, lift, and side-force coefficients to be measured at yaw angles up to 55 degrees. Next, experimental results are presented for the Ahmed Body back angle of 35 degrees, then compared to validate the computational model for ground vehicle aerodynamics. Afterwards, we investigated the effect of heavy rainfall (LWC = 30 g/m3) on the external aerodynamics of the utility truck with the morphing boom equipment using the validated computational fluid dynamics method, and the external flow is presented using a computer visualization. Finally, force & moment coefficients and velocity distributions around the utility truck are computed for each case, and the results are compared. Keywords: Experimental Wind-Driven Rain Wind Tunnel Testing, Heavy Rainfall, The Ahmed Body, Utility Truck, Morphing Boom Equipment, Discrete Phase Model (DPM), Automotive Aerodynamics, Computational Fluid Dynamics (CFD) 

Global climate change has affected the human race for decades. As a result, severe weather changes and more substantial hurricane impact have become a typical scenario. Utility trucks with the morphing boom equipment are the first responders to access these disaster areas in bad weather conditions and restore the damages caused by the disaster. The stability of the utility trucks while driving in a heavy wind scenario is an essential aspect for the safety of the rescue crew, and aerodynamic forces caused by the wind flow constitute a significant factor that influences the stability of the utility truck. In this paper, the aerodynamic performance of the utility truck is modeled using the incompressible unsteady Reynolds Averaged Navier Stokes (URANS) model. The Ahmed body, a well-recognized benchmark test case used by the computational fluid dynamics (CFD) community for the aerodynamic model validation of automobiles, is used to validate this aerodynamic model. The validated aerodynamic model investigates the impact of heavy wind on the utility truck with the morphing boom equipment. The visualization of the flow field around the utility truck with the force and moment coefficients at various side slip angles are presented in this paper. 

Flow around the Ahmed body is a well-recognized benchmark test case used by the computational fluid dynamics (CFD) community for model validation of automobiles. Even though the geometry of the Ahmed body is simple, the flow field around the object is complex due to flow separation and vortex shedding. In this paper, a Discrete Phase Model (DPM) based computational methodology is presented to estimate the effect of rain on aerodynamic performance and is validated with the experimental data that is available in the literature for the NACA64-210 wing section under different rain intensities. With this validated model, we have investigated the Ahmed body under low and high rain intensities for base slant angles of 25 and 35 degrees. The computed drag coefficient for the Ahmed body under rain conditions, are compared with the experimental data from aerodynamic analysis of the Ahmed body without rain, to evaluate the rain effect.