Experimental research on fluid elastic instability in tube bundles subjected to single-phase water cross-flow

The majority of failures in steam generators in the nuclear power plant can be attributed to flow-induced vibrations (FIV) resulting from the cross-flow on the shell side. Understanding the FIV characteristics of the tube bundle plays a significant key in engineering issues, such as the design of tube bundle arrangements and safety verification of equipment. This paper conducts a detailed investigation into the FIV characteristics of three types of arrays with normal triangular, parallel triangular, and rotated non-regular triangle in the cross flow. The effects of the array configuration, pitch ratio, and stiffness of surrounding tubes on FIV were analyzed. The theoretical model was modified based on the experimental data. The reduced velocity (V_p) was increased in a stepped manner during the experiment until the tube bundle was damaged, which led to the termination of the experiment. The range of V_p is 0–3.5. This study analyzed the frequency-domain and time-domain characteristics of three stages: turbulence excitation, vortex shedding, and fluid-elastic instability (FEI). The results indicate that within the range of 1.6 to 2.5, as the pitch ratio increases, the allowable inlet flow velocity becomes larger, and the tube bundle becomes more stable. Under small pitch ratios (less than 1.6), FEI is more likely to occur in the central tube. When the pitch ratio is larger (greater than 2.5), the FEI occurs simultaneously in the central tube and the downstream tube. It is also shown that there is a weak correlation between the V_pcr of transverse FEI and the pitch ratio. There is a strong correlation between the V_pcr of streamwise FEI and the pitch ratio. The coupling between tubes has a significant impact on the occurrence of streamwise FEI. Arranging rigid tubes around the tube is more stable than arranging flexible tubes. Based on the experimental data, the new theoretical model considers the specific variation of the V_pcr with the pitch ratio for rotating non-regular triangular structures. The instability constant is 2.54, and the exponent constant is 0.5.