Transient conjugate heat transfer in critical flow nozzles

The body temperature of critical flow nozzle is cooled by expanding cold gas. Subsequently, the thermal boundary layer and throat area are influenced by the conjugate heat transfer at the solid-fluid interface which is called thermal effect. This conjugate heat transfer process in nozzle flow with shock-induced separation were investigated experimentally and numerically, involving three-dimensional wall conduction and fluid convection. Numerical computations solved Reynolds-averaged equations based on SST k-ω model coupling with solid-phase heat conduction equation and were validated by some experiments. Three-dimensional separation criteria and the asymmetry of body temperature were investigated. The maximum asymmetry of body temperature appears at d = 5.25 mm and p0 = 4.5 bar. For this asymmetric flow, the experimental isotherm upstream of separation point obtained by twelve temperature points in different sides is accuracy which is enough to study the thermal effect and downstream isotherm with a maximum error of 0.5 °C is mapped merely for reference. At steady-state, minimum temperature point is close to separation point rather than nozzle exit. The body temperature gradually drops with the increase of throat diameter and inlet pressure. The maximum body temperature drop can reach to 15.0 °C. The detailed process of conjugate heat transfer was analyzed by Mach contour in fluid region, and isotherm, heatline in solid region. Finally, the dynamic response characteristics, especially thermal time constant of the body temperature were discussed.