Investigating the aerodynamic effect of rooftop cargo compartment – a case of modified intercity bus

Abstract

Abstract Buses are one mode of mass transportation but they are inefficient in terms of fuel consumption and ergonomically poor when loaded. Thus to decrease the fuel consumption, an improvement on the aerodynamic shape of the bus is required. This paper mainly focused on locally modified ISUZU buses which are serving as an intercity bus in Ethiopia. These buses are inefficient in terms of fuel consumption because of their body design and other add-on devices. One of the add-on devices which spoil the aerodynamic profile of this bus is the luggage loaded on the roof rack. Therefore, in this paper aerodynamically efficient rooftop luggage compartment is designed for these buses. The performance test is carried out for a scaled-down ISUZU bus model numerically using ANSYS Fluent CFD software and experimentally using wind tunnel testing. The numerical results are validated by an experimental test which is carried out using HM 170 open wind tunnel set-up. According to the numerical result, the modified bus reduced the drag coefficient by 34%, 34.5% and 34%, when compared to the clean roof baseline bus, the baseline bus with roof rack and the loaded baseline bus respectively. Similarly, the drag force is reduced by 12%, 14% and 32% respectively. In addition, the fuel consumption is reduced by 2.15 l h −1, 4.17 l h −1 and 7.24 l h −1 respectively. It is also found that the numerical results are in good agreement with the experimental results. Overall, the modified bus is found to be more fuel saving and ergonomically better design.