Flow Visualization and Particle Dispersion Measurements Inside an Ambulance Rear Saloon while Stationary and in Motion

Abstract

The following article presents flow field and particle dispersion data from a United Kingdom (UK) National Health Service (NHS) ambulance, under static and dynamic driving conditions and when using different ventilation modes. Data were recorded using laser sheet flow visualization, particle image velocimetry (PIV), and hot wire anemometry from a common plane positioned about the patient centerline. Results indicated a significant influence of the ceiling fan ventilation system on gross flow field behavior, with the ventilation fan on extract or intake mode. With either ventilation mode, flow velocities in the patient region were found to double from a quiescent condition to around 50-100 mm/s. Particle dispersion data also showed dispersion decay rates over five times faster when using the ceiling fan extraction system. All these results were consistent when the vehicle was stationary or driving at a constant speed of 60 mph. However, with the vehicle under dynamic driving conditions, such as acceleration or braking, the regular flow patterns were substantially disrupted, with the bulk movement of the flow in the direction of the acceleration or braking action. Under these dynamic conditions, the magnitude of the net velocity change on the fluid exceeded any flow generated from the ceiling ventilation system.