Flutter of Flexible Hydrofoil Struts 



DISCUSSION 



John P. Breslin 



Stevens Institute of Technology 

 Hoboken 3 New Jersey t U.S.A. 



If I understood correctly, Mr. Besch said that for the bending 

 type of flutter the correlation achieved was much better when one 

 used two-dimensional hydrodynamics than when one used three-dimen- 

 sional. If that is so, it is surprising to me, and I wonder if he could 

 tell us briefly what the three dimensional calculation included and what 

 it excluded ? 



REPLY TO DISCUSSION 



Peter K. Besch 



Naval Ship Research and Development Center 

 Bethesda 3 Maryland^ U.S.A. 



First of all, the two dimensional calculation consisted of 

 Theodorsen loading with a modification to allow for coupling between 

 bending and torsion due to the sweep angle. This is the NACA swept 

 wing flutter theory ; it was further developed by Yates at NASA to in- 

 clude spanwise variation in the two-dimensional lift slope and in the 

 two-dimensional aerodynamic centre location at each local position. 

 The calculation was further extended by us to include the modification 

 for spanwise variation of non-circulatory loading. So we have three 

 quantities varying in a spanwise direction to permit simulation of 

 three-dimensional flow. It seems that the first large improvement in 

 accuracy is obtained by including sweep angle. Further modification 

 which includes the load parameters I have just mentioned does not 

 produce generally accurate results. 



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