Investigation of the isolator flow of scramjet engines

摘要

This thesis focuses on the isolator of a Scramjet engine. The influence of wall and total temperature on the flow field is investigated with the help of different wind tunnel models. The wall temperature is varied from 300 K to 1000 K and the total temperature between 1150 K and 2200 K. The free stream Mach number is Ma∞ = 7.5. The experiments are supported by numerical flow simulations. In a typical Scramjet isolator with inlet the shock train as well as a shock boundary layer interaction are investigated. The experiments show that the relation between wall and total temperature is a good similarity parameter here. At constant back pressure the shock train grows upstream into the isolator with increasing wall to total temperature ratio. The flow field that enters the isolator is influenced by the inlet e.g. by the wall temperature. Also the investigated inlet produces an asymmetric profile entering the isolator. A model with rectangular cross section and homogenous inflow is investigated. The entering flow profile is also not influenced by any wall temperature. The isolator inlet Mach number is varied between 2 and 3.5. Here for constant back pressure the shock train length is decreasing with increasing wall temperature. This effect is most prominent when the wall temperature is getting close to the recovery temperature. Therefore the wall to total temperature ratio is not a similarity parameter here. The existing correlation by Waltrup and Billig cannot describe the observed effect quantitatively. It is modified based on the results and does now include the influence of the wall heat transfer. The influence of the flow channel width on the flow field is investigated with an additional model. In that model the isolator width can be varied. At a constant overall pressure rise the additional compression by the leading edge shocks of the side walls leads to a decrease of the shock train length. With increasing ratio between wall area and cross section (closing in on a quadratic cross section) the losses caused by the boundary layer increase and the shock train length is increasing.