For studying the complex flow structure of a high speed cavity, including shear layer, separation, reattachment and vortex, the single-color fluorescent oil flow visualization system in the 0.6m×0.6m trisonic wind tunnel of China Aerodynamic Research Development Centre was enhanced. Different portions of the cavity such as its bottom wall, left and right side walls, front and rear walls and area outside the cavity utilized different oil films with different fluorescent particles to visualize the flow mixing more effectively in the cavity. Specialized ultraviolet light sources are used to enhance the oil flow image contrast. Additionally, to ensure the oil film follows the surface streamlines and indicates the skin friction lines more accurately, the thickness and viscosity of the oil film are well controlled. A high-speed cavity wind tunnel test was conducted to validate the improved oil flow visualization system at Mach number ranging from 0.6 to 2.0. The experimental result shows that the improved oil flow system can effectively visualize complex flow patterns of the cavity flow at all Mach numbers. Colour fluorescent oil flow visualization system established in the present study provides a capability to visualize the flow mixing phenomenon in cavity flows with a high image contrast.

This paper presents a new-concept aircraft with a diamond joined-wing morphing configuration, which simultaneously adjusts the sweep angles of both the front wing and rear wings by a telescopic support rod. The compressible Navier-Stokes equations in the conservative form are solved to analyze the configuration characteristics and the aerodynamic benefits of this aircraft with different values of sweep angle (15°, 60°) and Mach number. The maximum lift-to-drag ratio is about 13.5 at M = 0.5 and α = 4 ° , 12.8 at M = 0.75 and α = 4 ° , and 3.4 at M = 1.5 and α = 6 ° , respectively. Compared with traditional morphing aircraft, the main advantages of this configuration include better transonic and supersonic performance, better lift characteristics in the state of a high-aspect ratio, and lower zero-lift drag in the supersonic state. The lift ratio of the front and rear wings shows a good similarity at different Mach numbers, especially for the 15° model, and the value eventually tends to be 1.3 at α = 12 ° . Meanwhile, the flow field characteristics and interference characteristics of the front and rear wings are studied. The increase in the angle of attack, incoming flow velocity, and distance between the front and rear wings can reduce the interference between front and rear wings. The influence from upstream components is proven to improve the aerodynamic characteristics of the rear wing, especially at α = 8 ° .

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