Pressure field propagation and mechanical vibration in a subchannel rig driven by a centrifugal blower

A six rod rig was built to study the structure of turbulent velocity and pressure fluctuations in a closely spaced square-pitched array of rods. An investigation was made of the spectra of the dynamic pressure and the structure vibration for the 45 kW centrifugal air blower; calming entry drum to the rig; and test section, as a function of Reybolds number, for the range of 104 to 2.4x105. The spectra showed that some of the lower frequency pressure components of the blower were propagating through 15 metre of 20 cm diameter ducting to the drum and test section, and exciting mechanical vibration of the test section. Approximate calculations of the possible flexural mechanical resonances of the system indicated that the frequencies contained in the pressure field were near some of the resonances, which would enhance the flow induced vibration. This far field pressure effect was most evident at the lower Reynolds numbers. As the Reynolds number was increased above 1.1x105, a large low frequency peak developed on the pressure spectra of the test section. (Auth.)