Numerical analysis of water phase transition effects in combustion-heated wind tunnels

Numerical analysis of water phase transition in combustion-heated wind tunnel is presented. In the numerical method used, high-temperature gas effect is combined within the inviscid flow. Source terms due to non-equilibrium condensation and evaporation are constructed with the homogeneous nucleation and droplet growth-shrink theory. Two cases are investigated in the present study. First, condensation of the water vapor, the by-product of combustion, in the expansion section of a very long nozzle with a designed exit Mach number 6, is analyzed. Eight cases with different total temperatures and different components of work gas resulting from different fuels combusted are simulated. Condensation takes place within a total temperature lower than 1700K. In these condensation cases, it is found that flow parameters at the nozzle exit deviate largely from condensed cases due to the release of the latent heat from condensation. The existence of condensation shock greatly deteriorates the uniformity of the flow at the nozzle exit. The results also indicate that condensation cannot be avoidable in simulating the flow condition of hypersonic flight at 220K temperature in a M6 nozzle. Then, droplet evaporation after compression by an oblique shock wave induced by a wedge placed in the tunnel's test section is considered. The inflow conditions such as Mach number, the static temperature and pressure, the liquid droplet number density, liquid mass fraction and droplet radius are taken from the outflow conditions of the M6 nozzle with condensation. The results reveal that flow properties after evaporation cannot recover to the flow without phase transition, which makes the model experiments in tunnel more uncontrollable. These all prove that water phase transition plays an important role in combustion-heated wind tunnel and should be studied intensively.