Investigation of Aerodynamic Effect of Rooftop Cargo Compartment for Locally Modified Intercity Bus Both Numerically and Experimentally

Abstract

Buses are the foremost important mode of mass transportation but they are inefficient in terms of fuel consumption. Thus to decrease the fuel consumption, improvement with in the aerodynamics of the bus shape is needed. This thesis mainly concerned about locally modified ISUZU buses which served as an intercity bus. These buses help the country in terms of transportation and knowledge transfer but they 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 roof rack which is used to load the passengers’ luggage. Most modern intercity buses have a separate luggage hold mounted below the passenger compartment. But, these locally modified buses are low floor buses in which it is very difficult to design a luggage compartment under the body. Therefore, using roof racks is the only alternative to transport the luggage. Unfortunately, the luggage loaded on the roof rack increased the aerodynamic drag; hence the fuel efficiency is affected. Therefore, in this thesis aerodynamically efficient rooftop luggage compartment is designed for locally modified intercity bus. The Aerodynamic analysis is carried out numerically using Computational Fluid Dynamics (CFD) and experimentally by wind tunnel testing. The CFD analysis is done on ANSYS Fluent using a scaled-down Isuzu Bus model which is modeled using CATIA V5. The experiment is carried out in Adama Science and Technology University using HM 170 open wind tunnel. According to the numerical result, the modified bus improved the drag coefficient by 34%, 34.5% and 34%, when compared to the clean roof baseline bus, the baseline bus without roof rack and the loaded baseline bus respectively, whereas the drag force is improved by 12%, 14% and 32% respectively. When comparing the modified bus with the loaded baseline bus the power requirement at 80 km/hr, 100 km/hr and 120 km/hr is reduced by 7655.23W, 14825.07W and 25741W respectively. In addition to that, the fuel consumption is improved by 2.15 L/hr, 4.17 L/hr and 7.24 L/hr respectively. The experimental result showed that, the drag coefficient of the modified bus is 0.487, 0.468, 0.461 and 0.452 at a speed of 5.6m/s, 11.2m/s, 16.8m/s and 22.4m/s respectively. The drag coefficient of the experimental result deviates from the numerical result by 8.64%, 7.83%, 7.45 and 6.35% respectively. However, according to many researches the percentage of the deviation is permissible.