Research on the Effect of Natural Ventilation on Buses in Summer Based on CFD Numerical Simulation Method

Abstract

Because of the relatively narrow space and high density distribution of the passengers, the bus interior environment deteriorates in summer. Natural ventilating introduces a fresh natural freeze, provides the bus interior with appropriate distribution of air supply temperature and velocity field. Making good use of natural ventilation is an operating strategy ideal for improving passengers’ satisfaction, which is considered as an environmental friendly and cost effective approach. Based on CFD numerical simulation, with a whole-domain approach, this paper predicts air flow and thermal comfort in naturally ventilated bus. The outside and inside airflow is modelled simultaneously and within the same computational domain. The thermal environment in different parts of the bus interior is compared. Different vehicle velocities and conditions of windows are taken into account, analysis are made regarding to the effect of both of them on the interior thermal comfort. The result shows, air disturbance at the bus rear parts are intenser than the other parts with better thermal satisfaction; the quality of air flow in different parts makes the temperature difference in bus achieve as high as 3°C; the use of roof openings distributes the temperature more evenly.

A frontal air intake may improve the natural ventilation in urban buses

“…In this situation, the position of air entries and exhausts, together with the amount of recirculated air or amount of fresh air added to the mixture, can be considered as design variables to test different ventilation modes and improve the expulsion of internal emitted aerosols. On the other hand, a second set of studies have simulated in-cabin turbulent flows formed at the expenses of the exterior air flowing through the open windows of the bus, or having no air conditioning system, as happens in many Latin American, Asian and African countries; these papers 8,[16][17][18][19] conform the main background of the present report. First of all, the majority of these studies have revealed a characteristic flow inside urban buses that may not be obvious at first glance: contrary to what we may expect, when a bus is moving at a certain speed having a fixed number of open windows, the exterior air enters from the back windows and then travels towards the front pushing or sweeping the aerosols from back to front, on average.…”

“…* email: jrvelez@ifisica.uaslp.mx contaminants generated by different arrangements of open windows; importantly, they remarked that opening the driver's window together with the windows located at the middle of the bus can led to an observable "pumping effect" which transports air form back to front, as already mentioned. Li's papers as well as other works 16,20,21 have focused mainly in the transport of pollutants generated outside the bus, such as engine exhaust gases, which can then infiltrate towards the interior of the bus, or in the temperature distribution inside the bus generated by the flow field and its impact on thermal comfort levels 17,19 . Only Zhang et al 8 have explicitly considered the problem of aerosols emitted and transported inside a bus but without following their expulsion to the exterior (also consult the work of Mesgarpour 22 on the spread of droplets inside a closed bus).…”

Natural Ventilation in Urban Buses: From Negative Pressure To Velocity-Driven Dispersion of Aerosols

“…In a first group of papers we can find those that considered turbulent flows inside a bus generated by an air conditioning system 8,[13][14][15] In this situation, the position of air entries and exhausts together with the amount of recirculated air or amount of fresh air added to the mixture can be considered as design variables to test different ventilation modes and improve the expulsion of internal emitted aerosols. There are other papers which, on the other hand, have simulated in-cabin turbulent flows at the expenses of the exterior air flowing through open windows (having no air conditioning systems, as in Latin American, Asian and African countries); these papers 8,[16][17][18][19] conform the main background of the present report. First of all, the majority of these studies have revealed a characteristic flow inside urban buses that may not be obvious at first glance: contrary to what we may expect, when a bus is moving at a certain speed having a fixed number of open windows, the exterior air flow is observed to enter from the back windows and then travels towards the front pushing or sweeping the aerosols from back to front, on average.…”

“…Li's papers as well as other works 16,20,21 have focused mainly on the transport of pollutants generated outside the bus, such as engine exhaust gases, which can then infiltrate to the interior of the bus, or on the temperature distribution inside the bus generated by the flow field and its impact on thermal comfort levels. 17,19 Only Zhang 8 have explicitly considered the problem of aerosols emitted and transported inside a bus but without following its expulsion to the exterior (also consult the work of Mesgarpour 22 on the spread of droplets inside a closed bus). It is therefore necessary to conduct a new study on the transport and expulsion of aerosols occurring across the open windows of an urban bus by solving the external and internal flows simultaneously.…”