Assessment of the hypersonic intake isolator and performance evaluation at various flight conditions

The major problem with the Scramjet engine is the starting and unstarting conditions, which depend on intake performance. Although the engine starts efficiently at designed conditions without any problem, at off-design conditions, due to misalignment of shocks, not satisfying either shock on the lip or shock on the shoulder and this leads to spillage flow and loss of total pressure. The intake design is modified to satisfy shock on shoulder condition to improve the operating range of the scramjet engine. Using ANSYS Fluent, Inviscid flow simulations are carried on modified design, it satisfied the shock-on-shoulder requirement, but in viscous simulations, the flow leads to unstarting conditions because of shock wave interaction with the boundary layer. Thus, shock on shoulder can be neglected in the design of hypersonic intake for scramjet engines. This paper analyzes a two-ramp, two-dimensional scramjet intake design using ANSYS Fluent. An elaborative CFD analysis was performed to estimate the efficiency of the hypersonic intake isolator because of changes in the flight conditions concerning free-stream conditions such as Mach number, angle of attack, and real-flow atmospheric conditions concerning altitude. This analysis shows that performance parameters such as total pressure recovery decreases during off design conditions. However, the normalized pressure ratio increases from 19 at Mach 4 to 72 at Mach 8. Due to an increase in the angle of attack, there is a increase in the pressure ratio and decrease in total pressure recovery. The flow separation bubble size increases as the Mach number increases leading to unstarting condition and increases as the angle of attack increases. An injection technique is used to suppress the flow separation. Out of the various orifices analysed the research concludes diamond shape injectors at 45° angle with total Nine injectors for mass flow rate not greater than 4% of intake mass flow satisfying all the performance parameters has reduced the flow separation bubble size from 4 mm to 0.95 mm in hypersonic intakes of Scramjet Engine at Mach 5.