Unsteady Interior Climate Simulation of Electric Buses

Examensarbete för masterexamen
Ravindra, Nithin Bharadwaj
In today’s world buses are one of the most popular means of transport for commuters in an urban setting. To maintain the thermal comfort of passengers inside the bus the heating, ventilation and air condition (HVAC) systems are used. These systems consume a large part of the total power consumption in the bus especially when working in extreme weather conditions. In urban areas, the energy lost to the external atmosphere is not only through the walls of the bus but also when the doors are opened for passengers to board or depart. The recent shift towards electrification of buses, especially in cities, makes analysing and reducing the power consumption of HVAC system ever so important. This study uses Computational Fluid Dynamics(CFD) to frame a methodology for simulating the interior climate of bus. Simulations offer a way to test various cases at relatively lower cost and faster rate when compared to experiments. In this study initially a steady state model is built using Reynolds Averaged Navier Stokes(RANS) equations and realizable k 􀀀 turbulence model with all the necessary HVAC system boundary conditions. The model is calibrated against the experiments by sweeping a scaling factor to find the heat transfer coefficient(HTC) of the exterior parts of the bus such as floor, roof, windows, walls etc. The calibrated model is then converted into an unsteady model using steady state simulation results as an initial solution. The unsteady model is built to simulate one standard door opening cycle, i.e, 20 seconds of opened door followed by 2 minutes of closed door simulation. The motion of the doors in the simulation is obtained by using overset mesh methodology. The model is built with one extreme weather condition of -8.3 C. The results from steady state describing the flow behaviour of the interior climate and the effect of door opening cycle on the interior climate from unsteady simulation are discussed in this study.
Interior Climate, HVAC, CFD, Overset mesh, Electric bus, Unsteady simulation
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