Авіаційно-космічна техніка та технологія (Aug 2021)
Simulation of flow in a tandem fan of a turbofan engine
Abstract
Modern trends in the global aircraft industry are prompting aircraft engine engineers to create and develop various methods to improve the aerodynamic characteristics of turbomachines. The urgent need to improve the efficiency of new generation engines leads to a rapid increase in the bypass ratio of engines, which requires the development of fans with large diametrical dimensions and high aerodynamic perfection. Boundary layer control in turbomachines using tandem blade rows is one of the most promising ways to improve the aerodynamic characteristics of aircraft engine fans with a high bypass ratio. The work aims to evaluate the aerodynamic characteristics of a fan with a tandem impeller for a turbofan engine. Two fan impellers were investigated: a single-row and an equivalent tandem-row (the equivalence was ensured by the equality of the structural angles of the flow inlet and outlet and the equality of the chord of the profiles). The blade row consisted of 33 blades, the tip diameter at the inlet to the impeller was 2.37 m, the hub diameter was 0.652 m. The flow was simulated in the range of axial velocity at the inlet from 80 to 200 m/s at a relative rotor speed of 0.65, 0.85, and 0.9. For the investigated tandem fan impeller, the chord of the first row was 60% of the total chord of the profile, the length of the slotted channel was 10% of the total chord. The flow was simulated using a numerical experiment. When closing the system of Navier-Stokes equations, Menter's SST turbulence model was used. The computational grid is unstructured, with an adaptation of the boundary layer. The work shows that the use of a tandem impeller will improve the aerodynamic characteristics of the fan. As a result of the study, it was found that the pressure ratio in a fan with tandem impeller increases from 0.32 to 20% for an operating mode at a relative rotor speed of n=0.65, n=0.85, and n=0.9 in the range of values of the gas-dynamic flow rate function q (λ)=0.4...1. The greatest growth is observed on the left branches of the pressure lines. The obtained data on the efficiency of a fan with a tandem impeller showed that in the range of values of the gas-dynamic flow rate function q(λ)=0.4...0.6 and q(λ)=0.76...0.98 a tandem impeller is higher than the efficiency of a fan with a single-row impeller, for values of the gas-dynamic flow function q(λ)=0.64...0.76 - the efficiency of a fan with a tandem impeller is 4% less than the efficiency of a fan with a single-row impeller.
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