Mechanism of unsteady aerodynamic heating with sudden change in surface temperature

Abstract

The characteristics and mechanism of unsteady aerodynamic heating of a transient hypersonic boundary layer caused by a sudden change in surface temperature are studied. The complete time history of wall heat flux is presented with both analytical and numerical approaches. With the analytical method, the unsteady compressible boundary layer equation is solved. In the neighborhood of the initial and final steady states, the transient responses can be expressed with a steady-state solution plus a perturbation series. By combining these two solutions, a complete solution in the entire time domain is achieved. In the region in which the analytical approach is applicable, numerical results are in good agreement with the analytical results, showing reliability of the methods. The result shows two distinct features of the unsteady response. In a short period just after a sudden increase in the wall temperature, the direction of the wall heat flux is reverted, and a new inflexion near the wall occurs in the profile of the thermal boundary layer. This is a typical unsteady characteristic. However, these unsteady responses only exist in a very short period in hypersonic flows, meaning that, in a long-term aerodynamic heating process considering only unsteady surface temperature, the unsteady characteristics of the flow can be ignored, and the traditional quasi-steady aerodynamic heating prediction methods are still valid.

Study on the Unsteady Aerodynamic Heating of the Oscillating Model

“…8 we can see that the pressure of the physical stagnation point has little difference with the steady state, and the heat flux of the physical stagnation point has a little difference with the steady state.…”

A theoretical study on the unsteady aerothermodynamics for attached flow models

“…The flow on a flat plate of a dimensionless length 10 was simulated, with the grid and time step verified. For the details of the numerical method, please refer to [15]. To evaluate the strength of flow unsteadiness, we compared the results computed by the unsteady approach to the corresponding results computed by the steady approach.…”

“…For instance, refs. [12][13][14] are some of the representative works, and the authors also have done some analytical work [15]. Indeed, due to the rapid development of the computational techniques, numerical simulation has become the most direct approach to specific problems, but for the sake of understanding the physical nature of the problems, theoretical works are essential.…”