Advances in the research of ultra-compact transition between high and low pressure turbine stages in the Engineering Thermophysics Institute

In order to pursue higher economic efficiency (high propulsion efficiency, low fuel consumption rate, etc.) and environmental friendliness (low pollution emission, low noise, etc.), modern high-performance civil turbofan engines generally adopt higher bypass ratios. The low-pressure turbine is coaxial with the fan. Because of the limitation of the tip speed of the fan (import shock, noise, and strength), the low-pressure rotation speed often cannot be designed too high. Taking into account the requirements of the output power of the low-pressure turbine, the reduction of the rotational speed will bring difficulties to the aerodynamic design of the low-pressure turbine. In order to solve this contradiction, it is usually necessary to increase the radial position of the low pressure turbine rotor, resulting in an increase in the radial height difference between the high and low pressure turbine rotors, and switching between the high pressure turbine and the low pressure turbine by means of a transition section with a large change in curvature. .

The researchers of the Light Power Laboratory of the Institute of Engineering Thermophysics, Chinese Academy of Sciences focused on the flow field coupling analysis of the high-expansion S-shaped transition section and the curved wide-chord-long low-pressure turbine guide, and was built with the light power key laboratory of the Chinese Academy of Sciences. The large-scale (low-speed) annular wind tunnel experimental platform (Fig. 1) adopts seven-hole probes and the dynamics of multi-section aerodynamic parameters under the condition of low Reynolds number and pre-rotary flow inlet and outlet conditions to simulate the real environment of the engine. The data acquisition method analyzes the flow field structure in the S-shaped transitional channel and downstream of the guider; uses the multi-channel surface hot film dynamic experimental data test analysis method to grasp the surface of the wide chord-length low pressure turbine guide built in the S-type transitional section. The dynamic transfer characteristics of the boundary layer; and under specific conditions, according to actual needs in the experimental process using three-dimensional hot-wire and oil flow display method for flow field testing.

Through experimental measurements and numerical simulation methods, the following progresses have been made: 1. The transition section of the integrated ultra-compact S-type high-low pressure turbine uses a wide chord-length guide coupling design, which is an effective alternative to conventional high-low pressure turbine transition sections. With the help of the wide chord guide vane, the passage area in the transition section is improved, the three-dimensional separation due to the vortex caused by the casing in the ultra-compact transition section is alleviated, and the flow loss in the ultra-compact transition section is facilitated; 2. The wide chord guide is eliminated. In the latter half of the tunnel, the radial radial pressure gradients of the tunnel rims are affected by the radial pressure gradients of the rotors toward the hub. At the outlet of the deflector, the impact range moves to approximately 45% of the leaf height (Fig. 2). Induced eddies are formed between the vortexes of the hub and the hub, resulting in an increase in the total pressure loss. 3. To reduce the flow loss of the wide chord-length guides, the guide vanes can be modified by the leaf-shape stacking method, including: (1) Moderate blade deflection Tilt, anti-dip through the blade can reduce the circumferential pressure gradient of the end wall of the casing, which is beneficial to weaken the vortex strength of the top channel, but with the increase of the tilt angle, the radial pressure gradient of the second half of the guide from the casing to the hub is enhanced. , leading to vortex radial migration of the top of the leaf channel, which is not conducive to reducing the secondary flow loss; (2) blade bending. The vortex of the top chord of the wide chord-length guide in the region of the outlet leaf interacts with the induced vortex to increase the secondary flow loss, and the radial pressure gradient of the main flow direction toward the end wall is constructed by the reverse bending of the leaf blade, and the vortex leaf of the leaf top channel is suppressed. The development of the medium direction can reduce the secondary flow loss of the wide chord guide channel.

The above research was supported by the National Natural Science Foundation of China. The relevant research results were published in Science China and Thermal Science.

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