With the emphasis lying on increasing fuel efficiency of vehicles in order to combat rising fuel prices and environmental challenges the manufacturers are thinking beyond the conventional vehicle systems by focusing on its aerodynamics. Aerodynamic drag exceeds 50 per cent of the total resistance to motion at speeds above 70km/hr, and above 100 km/hr it is the most important factor. The review is done to identify the various shortcomings of the automotive designers when it is in regards to flow separation of air at the rear of the vehicle which causes most of the losses. This paper focuses on the work already done in the field of aerodynamics starting with Ahmed Body. It is a bluff body with adjustable rear slant angle and the basis upon which the aerodynamicists test their models. And then, moving onto passive aerodynamic enhancements for automobiles like vortex generators and diffusers whose various dimensional modulations were discussed with several steps leading to its advancement in vehicle body design. This brings to the simulation, Computational Fluid Dynamics (CFD) and its role in this analysis was covered. CFD has been modified a lot from the beginning to increase the accuracy of its predictions. So the paper lists various simulation techniques studied by the previous researchers in order to understand the wake region behind the car which has been notoriously difficult to predict till date. Several aspects of aerodynamic drag that need further analysis to improve the aerodynamic were highlighted.

In this paper, a critical mass flow rate (CMFR) has been obtained for three different steam generators (i.e. two marine-type and one commercial) at different inlet void fractions using the CFD method to study the sustainability of natural circulation (NC) due to depressurization in two-phase NC mode. Because of depressurization, the transients in the inlet void fraction have been considered as multiple steady-state inputs, and the range of safe operating mass flow rate has been obtained. The results show that the characteristics curves shift with inlet void fraction thus limiting the operating mass flow rate range between 0.046 kg/s to 0.050 kg/s for M_SG1 and 0.051 kg/s to 0.055 kg/s for M_SG2. The effect of pipe roughness on CMFR has also been studied. The results can be used for the optimized design of the U-tube steam generator (UTSG) that will safely perform the heat removal operation during a small break loss of coolant accident (SBLOCA).