The instability of rod arrays due to impinging jet flow is investigated. The objective is to provide the basis for development of design guidelines to avoid detrimental vibrations of nuclear fuel rod arrays in a PWR induced by baffle jet. The arrays are of the in-line type with a pitch ratio of 1.33, and the fuel rod is simulated as a single span simply supported beam.
Similarity parameters for valid model tests are discussed. The criterion for the stability of a rod array is given by these dimensionless parameters in the form of
$\frac{V_c}{f_nD} = K \sqrt{(\frac{D}{h})(\frac{m_oδ_o}{\rhoD^2})}$
The value of proportionality constant K which characterizes the stability boundary is determined by measuring dynamic responses of the rod array for various values of each system parameter. By adopting two kinds of rod material (aluminum and brass), natural frequency $f_n$ and damping parameter change their values. And testing apparatus is so designed that the slit width h can be varied arbitrarily. Based on the data obtained during the experiments, the value of K is estimated as 2.78 with its lowest value of 2.59.
