Aerospace Flight Modeling and Experimental Testing

Validation processes for aerospace flight modeling require to articulate uncertainty quantification methods with the experimental approach. On this note, the specific strategies for the reproduction of re-entry flow conditions in ground-based facilities are reviewed. It shows how it combines high-speed flow physics with the hypersonic wind tunnel capabilities.

Computational studies to determine the design of prototype heater for a hypersonic wind tunnel

During the modernization of the TsAGI hypersonic wind tunnel, which implies an increase in the limiting values of the flow stagnation parameters, and in the thermal load, consequently, computational studies were realized for the existing design of the electric arc heater and new geometry options for the central electrode and the cooling duct of the external electrode and nozzle. The distribution of the heat flux density to the surfaces of the main elements of the wind tunnel was obtained based on the calculations for the air duct of wind tunnel. The qualitative data of the flow formation both in the pre-heater and the pre-chamber served as the basis for changing the geometry of the central electrode. In this study, a numerical modelling approach was implemented for a through calculation of the flow and heat transfer in all areas of the wind tunnel circuit (heater, pre-chamber, nozzle, test section, diffuser). The ANSYS FLUENT software package was used to solve the axisymmetric Navier-Stokes equations for a five-component chemically reacting gas mixture: O2; N2; O; N; NO using the Spalart-Allmaras turbulence model. To study the hydrodynamics and thermal state of the structure of the external and central electrodes, the possibility of the ANSYS FLUENT complex for solving conjugate problems was used (the complete Navier-Stokes equations and the energy balance equation were solved in a fluid, and the heat conduction equation was solved in a solid). In this case, at the interface between the media, the conditions for the continuity of temperature and heat flux were satisfied.

Developing and applying Mach 4.5 nozzle in hypersonic wind tunnel

Mach 4.5 tests in a conventional trans-supersonic wind tunnel are often accompanied by the air liquefaction phenomenon, resulting in the low reliability of test data. The Mach 4.5 nozzle developed in a hypersonic wind tunnel is able to heat airflow and provide more accurate test data. At present, China does not have the capability to test the Mach 4.5 nozzle in the 0.5-meter hypersonic wind tunnel. This gap may be filled by developing the Mach 4.5 nozzle in the hypersonic wind tunnel. The axisymmetric nozzle profile was calculated by the inviscid flow calculation method, and the boundary layer was modified by the Sivells-Payne method. Then, the numerical simulation was carried out, and the simulation results prove that the nozzle profile thus calculated meets the design requirements of the Mach number. For its structural design, a three-section design method is adopted to ensure the continuity and smoothness of the inner surface so as to better calibrate the flow field. Standard model tests were also carried out. The test results show that the velocity field of the Mach 4.5 nozzle we developed meets technical requirements. The standard model test data provide data reliable support for the development of aircraft.

A novel method to realize a non-uniform heat flux distribution through the variable-speed scanning of an electron beam

Quartz lamp heaters and hypersonic wind tunnel are currently applied in thermal assessment of heat resistant materials and surface of aircraft. However, it is difficult to achieve precise heat flux distribution by quartz lamp heaters, while enormous energy is required by a large scale hypersonic wind tunnel. Electron beam can be focused into a beam spot of millimeter scale by an electromagnetic lens and electron-magnetically deflected to achieve a rapid scanning over a workpiece. Moreover, it is of high energy utilization efficiency when applying an electron beam to heat a metal workpiece. Therefore, we propose to apply an electron beam with a variable speed to establish a novel method to realize various non-uniform heat flux boundary conditions. Besides, an electron beam thermal assessment equipment is devised. To analyze the feasibility of this method, an approach to calculate the heat flux distribution formed by an electron beam with variable-speed scanning is constructed with beam power, diameter of the beam spot and dwell duration of the electron beam at various locations as the key parameters. To realize a desired non-uniform heat flux distribution of the maximum gradient of 1.1 MW/m3, a variable-speed scanning strategy is constructed on basis of the conservation of energy. Compared with the desired heat flux, the maximum deviation of the scanned heat flux is 4.5% and the deviation in the main thermal assessment area is less than 3%. To verify the method, taking the time-average scanned heat flux as the boundary condition, a heat transfer model is constructed and temperature results are calculated. The experiment of variable-speed scanning of an electron beam according to the scanning strategy has been carried out. The measured temperatures are in good agreement with the predicted results at various locations. Temperature fluctuation during the scanning process is analyzed, and it is found to be proportional to the scanned heat flux divided by volumetric heat capacity, which is applicable for different materials up to 3.35 MW/m2. This study provides a novel and effective method for precise realization of various non-uniform heat flux boundary conditions.