RESEARCH ON THE HYDRODYNAMIC CHARACTERISTICS OF CAVITATING GRID FINS

A two-phase mixture model based on the solution for the Navier-Stokes equations has been utilized in calculating the hydrodynamic characteristics of cavitating honeycomb grid fins with different configurations. The calculation results of lift, drag, and hinge moment coefficients are presented in various cavitation numbers and angles of attack, and its hydrodynamic features are also analyzed. The calculation results indicate that cavitation will reduce the lift/drag ratio of grid fins. The increment of horizontal blades as lift surface cannot unendingly improve lift because of the disturbance between the blades.

RESEARCH ON HYDRODYNAMIC FORCES OF CAVITATING GRID FINS

Hydrodynamic forces and flow pattern of four kinds of cavitating grid fins with cavitation number from 2.5 to 0.25 were simulated numerically with a bubble two-phase flow model embodied in the commercial CFD code Fluent 6.0. Comparison with experimental datum showed that rules of hydrodynamic forces changing with cavitation number were coordinated with experiment, and cavitation made the ratio of lift to resistance decrease. Calculated axial force and chordal pressure center in all-wetted condition or those at cavitation number less than 0.75 agreed well with experiments. Normal force in all-wetted condition was less by 20 per cent. The differences between computation and experiment in the total range of cavitation number were mainly because that the incipient cavitation number in computation was less than that at experiment.

Navier-Stokes Computation of Grid Fin Missile Using Hybrid Structured-Unstructured Grids

Viscous CFD computations are performed to predict the aerodynamic coefficients and flowfield for a missile with grid fins by using hybrid grids. The computations arc made at Math numbvrs of 0.7 and 2.0. Full N-S equations arc discretized into finite volume form and solved by an algorithm in LU-SGS. The comparisons between computation and experimental data are made, and the detailed flow structure near grid fin is shown and examined.

The research analysis of aerodynamic numerical simulation of grid fin

This paper presents the results of an investigation to use arc-length mesh generation and finite volume TVD scheme to calculate Euler equations for predicting the effect of geometry parameters in reducing the drag force and improving the lift-drag ratio of grid fin in the supersonic flow regime. The effects of frame and web, whose cross section shape and thickness and spacing,on the aerodynamic character of the grid fin were studied. Calculations were made at Mach 2.5 and several angles of attack. The results were validated by comparing the computed aerodynamic coefficients against wind tunnel experimental data. Good agreement was found between computed and experimental results. The computed results suggest that parameters of the grid fin's frame have the greatest effect on the grid fin aerodynamic character, especially on its drag force. It was concluded proper choice of appropriate grid fin geometry parameters could reduce the drag force and improve the lift-drag ratios.

Numerical studies of static aeroelastic effects on grid fin aerodynamic performances

The grid fin is an unconventional control surface used on missiles and rockets. Although aerodynamics of grid fin has been studied by many researchers, few considers the aeroelastic effects.In this paper, the static aeroelastic simulations are performed by the coupled viscous computational fluid dynamics with structural flexibility method in transonic and supersonic regimes. The developed coupling strategy including fluid–structure interpolation and volume mesh motion schemes is based on radial basis functions. Results are presented for a vertical and a horizontal grid fin mounted on a body. Horizontal fin results show that the deformed fin is swept backward and the axial force is increased. The deformations also induce the movement of center of pressure, causing the reduction and reversal in hinge moment for the transonic flow and the supersonic flow,respectively. For the vertical fin, the local effective incidences are increased due to the deformations so that the deformed normal force is greater than the original one. At high angles of attack, both the deformed and original normal forces experience a sudden reduction due to the interference of leeward separated vortices on the fin. Additionally, the increment in axial force is shown to correlate strongly with the increment in the square of normal force.