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For the coincidence degree, the NACA0012 combined cascade is taken as an example. The experimental results of the coincidence (positive) B=0%, 30%, 50%, and 100% were studied. When the trailing cascade is fully inserted into the front cascade, B=100%. In order to meet the joint working conditions, the inlet flow field must be in the area 1, and the flow rate is distributed, so that the front inlet angle of the blade is reduced, and the function is reduced. The inlet angle of the trailing blades is increased, and the function is improved. Since the trailing cascade cascades toward the tail of the blade, the boundary layer cannot quickly bear the load due to the increased angle of attack, and the separation occurs first at the leading edge of the blade. The separation of the trailing vane airflow rapidly deteriorates the flow field of the entire combined cascade. Since the front row cascade is completely inserted into the front cascade, the mutual interference and induction between adjacent blades are maximized. Therefore, the airflow of the trailing blades is separated, so that the back-arc gas flow of the front blades is also quickly encountered. damage. When AN is equal to 12.7b, the combined cascade has completely stalled, and at this time, the front cascade is far from the angle of attack of its maximum lift, and the front cascade is far from playing its due role, and the result ultimately leads to CN. +Rymax, AN+RCymax drop.
In short, when B is too large, the separation of the trailing blades prematurely, which seriously affects the flow conditions of the front cascade, greatly reduces the amount of airflow around the airfoil, and not only reduces the lift level of the combined cascade, but also It also increases the resistance of the wing. When B=0%, there is no flow field coincidence between the two rows of cascades before and after the combined cascade, and the outlet of the front cascade directly becomes the inlet of the trailing cascade. The airflow carries a large number of wake vortices into the trailing cascade, and the flow field of the entire trailing cascade is filled with eddy currents. When AN is equal to 13.6b, 95% of the boundary layer on the airfoil of the trailing blades becomes almost turbulent. At this time, due to the flow of the trailing cascade, the exit condition of the front cascade is deteriorated, so that the flow of the front side of the blade is destroyed, causing the front blade to separate the airflow in advance, and the amount of the airfoil decreases and the lift decreases. . When BU 30% is 50%, the aerodynamic performance of the combined cascade is significantly improved. The separation point of the front arc surface of the front row is obviously rearward, and the induction between adjacent blades will vary along the chord length. In the region, the influence of the trailing blades on the preceding blades will be reduced, while in the region, the induction between the front and rear cascades is enhanced.
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