A high speed camera was used for interferometry visualization (in di®erent phases of the motion) of the°uttering NACA0015 pro¯le supported in a translational and rotational manner. First, the simpli¯ed mathematical model of the support of investigated pro¯le was identi¯ed from minimum least squares di®erences between modeled and measured system responses. A special graphical Matlab procedure was proposed for evaluation of interferograms. Kinematic analysis de¯ning motion of the pro¯le as a function of time was obtained by a regression using the least squares method. Numerical integration of pressure functions around the airfoil surface allows for calculation of the resulting aerodynamic forces and moments.
Experimental facility situated in the test section of the wind tunnel suction type was adjusted both in the total construction and in the construction of the fluttering body, the methodology of the measurement and evaluation of the flow and dynamic parameters during flutter were also changed. Preserved was the conception of the NACA0015 profile with two degrees of freedom, rotational and translational. Torque elasticity was now realized by the coil spring and changed by different length of this spring or by different diameter of the spring wire. The pitch angle of the profile was now measured by the magnetic rotary encoder. The translational position was indicated by the magnetic linear encoder and was centered by plane springs situated on both ends of the shiftable frame. With this model the testing measurement was realized by its self-excited vibration of flutter type in the range of Mach numbers M=0.20-0.215 and Reynolds numbers 263 000 – 283 000. Results obtained with M=0.21 and Re=276 000 are presented.
Natural frequencies and the thresholds for loosing the stability of thin-walled cylindrical shell conveying by flowing fluid are theoretically studied. Potential flow theory for fluid and 3D theory for thin shells are used. The shells of finite length are considered for the different case of boundary conditions at the edges of the shell, and their influence on the critical flow velocities for flutter are demonstrated. The fundamental importance of boundary conditions considered for fixing the edges of the cylindrical shell of finite length is shown. When the clamped - simply supported boundary conditions are assumed, the critical flow velocity for flutter is very low, even if the energy dissipation due to the fluid viscosity was taken into account.
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