With the rapid development of wide-speed-range aircraft development technology, there is an urgent demand for ground test equipment capable of simulating different flight speeds. As a key ground test facility, the variable Mach number wind tunnel can effectively realize the change of flow field parameters without replacing the nozzle, which not only enables the acquisition of experimental flow fields with different Mach numbers but also can be used to simulate the acceleration and deceleration processes of wide-speed-range aircraft. Traditional continuous variable Mach number supersonic wind tunnels usually operate in the Mach number range of 3 to 4, and increasing their upper operating limit to 4.5 can significantly expand the working speed range of such wind tunnels. This improvement is of great academic research and engineering application value, as it can better meet the test needs of advanced wide-speed-range aircraft. Currently, developing a variable Mach number wind tunnel with a low-complexity adjustment mechanism and capable of achieving continuous wave elimination in a wide speed range has become an important research direction and a core technical breakthrough goal in the field of aerodynamic test equipment.

To achieve the above research objectives, a combination of aerodynamic design, numerical simulation, and Mach number measurement experiments was adopted as the main research methods. First, the overall aerodynamic design of the variable Mach number wind tunnel was carried out, focusing on the optimization design of key components to ensure the rationality of the wind tunnel structure and the stability of flow field parameters. Then, numerical simulation was used to simulate the flow field characteristics of the wind tunnel under different Mach number conditions, verify the design scheme, and provide a theoretical basis for the physical construction of the test section. Finally, Mach number measurement experiments were conducted on the built wind tunnel prototype to test the actual performance of the wind tunnel, verify the accuracy of the numerical simulation results, and analyze the factors affecting the test results.

The research results show that a supersonic continuous variable Mach number wind tunnel with single-degree-of-freedom adjustment was designed, with a Mach number working range of 3 to 4.5. The wind tunnel system adopts an air-breathing layout, which effectively improves the stability and efficiency of the flow field. The core component, the nozzle structure, uses a rotation-type adjustable wall, and the design content includes the contraction section, the expansion section, and viscous correction. Numerical simulation results accurately provide the size of the effective area at the nozzle exit under different Mach number conditions, and it is verified that the flow field at the test section is uniform and free of shock waves when the Mach number is in the range of 3 to 4.5. Mach number calibration experiments show that the Mach number uniformity of the spanwise centerline at the nozzle exit is high, and the measured Mach number values are consistent with the Prandtl-Meyer expansion theory in the range of 3 to 4.5. In addition, the causes of Mach number errors in the experiment were analyzed, mainly including the influence of viscous effects at the nozzle wall.

In conclusion, the supersonic continuous variable Mach number wind tunnel with single-degree-of-freedom adjustment successfully expands the Mach number range from the traditional 3-4 to 3-4.5. The flow field in the effective area of the wind tunnel test section is uniform and stable, without shock wave interference, which meets the basic requirements of aerodynamic tests. The Mach number at the nozzle exit is in good agreement with the Prandtl-Meyer expansion theory, which verifies the rationality of the aerodynamic design of the nozzle. The wind tunnel adopts a single-degree-of-freedom adjustment mechanism, which effectively reduces the complexity of the equipment and realizes the function of continuous variable Mach number in a wide speed range. Overall, the wind tunnel meets the designed goals of simple operation and wide-speed-range continuous variable Mach number, which can provide reliable test support for the research and development of wide-speed-range aircraft and promote the progress of related academic research and engineering application.