Turbulent Air Flow Characteristics in a Ventilated Hospital Railway Coach

The aim of this work is to investigate turbulent air flows, through measurements inside railway coaches employed for the transport of sick persons. In this kind of environment, assuring occupant comfort and eliminating potentially annoying draught is necessary for safeguarding patients inside the train. As it is known, air velocity is not uniform but, instead, it fluctuates. It is these fluctuations that are the origin of local discomfort. This can result in a draught, which is defined as a local undesired cooling of the body. Since draught is one of the most common causes of complaint in a ventilated or air-conditioned space, understanding the turbulent air flow in these spaces and the impact of this flow on the sensation of draught is very important. The characteristics of turbulent air flow have been investigated through experimental measurements inside a railway coach provided with stretchers. In particular, in order to characterise these air flows, some parameters have been used, including mean velocity, standard deviation of velocity, turbulence intensity, and energy spectrum, etc. These parameters have been introduced by making use of the statistical analysis of instantaneous velocity measurements performed at several points. These were taken to be representative of the whole space actually occupied. This analysis showed that micro-nozzle diffusers gave optimum comfort conditions for patients in this type of hospital train.