Theoretical Modelling of Aeroheating on Sharpened Noses Under Rarefied Gas Effects and Nonequilibrium Real Gas Effects

In the first chapter, it has been mentioned that the utmost critical points concerning thermal protection are the stagnation point of the leading edge and the reattachment point behind a separation flow region. The wall surfaces near these points suffer from peak heat fluxes, and thus the surface temperature is relatively higher than elsewhere. These most dangerous regions are likely to be ablated first, and should be specially protected by UHTC materials. Therefore, our target is currently focused on the prediction of aeroheating performance of the typical stagnation point region, although the methodology and some conclusions are universal to an extent. In fact, we have found that the engineering theory established at the stagnation point region is also useful for analogy analysis of other regions.

The nonequilibrium flow behind a strong normal shock wave is a typical and classical topic for discussion. In theoretical research, Lighthill [1, 2] and Freeman [3], etc. have introduced the landmark ideal dissociating gas (IDG) model in 1950–1960s. By introducing the concept of the degree of dissociation in a dissociation-recombination reaction, they built the conservation equations and the state equation for a nonequilibrium dissociating gas, which greatly simplified the analysis and calculation on the nonequilibrium flow field behind a shock wave. Freeman also approximately analyzed the equilibrium degree of dissociation and characteristic nonequilibrium scale by using the semi-analytical semi-numerical method. Subsequently, based on this theoretical model, many other scholars [4‐7] have carried on further or more in-depth analyses on the related flow problems.

In the Chap. 2, we discussed the pure rarefied gas effects on aeroheating of sharpened leading edges of vehicles, assuming that the real gas effects are relatively unimportant. Afterwards, in the Chap. 3, we discussed the pure nonequilibrium real gas effects on flows behind strong normal shock waves. Since there is no characteristic scale of the macroscopic post-shock flow, the rarefied gas effects do not appear. In this chapter, we deal with the nonequilibrium real gas effects on the flow and heat transfer along the stagnation streamline toward a slightly blunted nose. In this flow problem is involved three characteristic length (or time) scales, i.e., the characteristic scale of the macroscopic flow, the characteristic nonequilibrium scale of the chemical reaction, and the MFP of molecules in the gas flow. Thus, it is probable that the rarefied gas effects and the nonequilibrium real gas effects arise simultaneously, and the coupling effects between them could also be significant, which makes it more difficult to understand the complex flow and heat transfer mechanism and to predict the aeroheating performance.

In order to solve one of the key problems in the TPS design of new generation vehicles, the theoretical modeling method was used in this thesis to study the aeroheating characteristics of sharpened leading edges under coupling rarefied gas effects and nonequilibrium real gas effects, and to establish a corresponding engineering theory framework.