Three-dimensional Blade Flutter Associated With Leaf Design

The flutter is one of the main obstacles in the development of turbomachinery. There are many of blade fracture accidents, which are due to the flutter of blade. The modern turbomachinery design trend of higher power, higher load and higher performance, the blade design trend of higher length and lighter weight, which has made current blade rigidity lower and lower. So the blade aeroelastic instability—flutter is likely occurred. Therefore, in the research of turbomachinery aeroelastics, it is more and more important to predict blade flutter and to avoid blade flutter. Based on the Computational Fluid Dynamics and Structural Dynamics methods, a numerical analysis and prediction system for the 3D blade flutter in turbomachinery was established. Applying this numerical flutter analysis and prediction system, a straight cascade and a 3D fan cascade were tested. Then, through changed design parameters of the two kinds of blade shape, the relevancy of 3D cascade flutter and cascade design was studied.Third order accuracy non-oscillatory and non-free-parameter dissipation difference scheme (NND) were adopted to solve the Navier-Stokes equation in the three-dimensional vibrating cascade unsteady viscous flow calculation. Thus, the high spatial resolution and the correctness of shape and location of the shock in transonic flow were taken into consideration. The Baldwin-Lomax turbulent model was adopted, which is an algebra model, and does not increase the number of equations and easy to solve. With respect of the unsteady flow, an implicit dual-time stepping method was employed, which can greatly decrease the calculating time of the three-dimensional unsteady flow in vibrating cascades to satisfy the engineering practice requirement.The value of unsteady aerodynamics on the blade was computed throughthe three-dimensional numerical simulation of the vibrating cascade flow combined with the structural dynamics analysis of vibrating blade. Finally, the probability of blade flutter was evaluated by energy method. Then, the numerical analysis and prediction system for the 3D blade flutter was established. By using the numerical flutter analysis and prediction system, a straight cascade and a 3D fan cascade was evaluated.Based on the straight cascade and the fan cascade, the design parameter of aspect ratio, maximum relative thickness and solidity were remodeled by programmed design method. And the intrinsic relation between cascade flutter and cascade design was studied by using the numerical flutter analysis and prediction system.Furthermore, the fan blade was stacked renewedly. And then, the influence of blade sweepforward, sweepback and bend on the cascade flutter was discussion. The results show that the efficiency of cascade would be more or less improved by the blade sweepforward, sweepback and bend, but the influence of them on the cascade flutter is various.