Flow visualization and particle dispersion measurements inside an ambulance rear saloon while stationary and in motion

The following paper presents flow field and particle dispersion data from a UK National Health Service (NHS) ambulance, under static and dynamic driving conditions and when using different ventilation modes. Data was recorded using laser sheet flow visualisation, particle image velocimetry and hot wire anemometry, from a common plane positioned about the patient centreline. Results indicated a significant influence of the ceiling fan ventilation system on gross flow field behaviour, 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 50mm/s – 100mm/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 60mph. However, with the vehicle under dynamic driving conditions, such as acceleration or braking, the regular flow patterns were substantially disrupted, with 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.