Experimental Studies on Twelve Bladed Fan Vibration Considering Flexibility of Shaft Shashank Shekhar Singh and Ahmad Ali Khan Abstract A fan rotor system can generate a large amplitude blade-passing frequency (BPF) component if the gap between rotating fans and stationary diffusers is not equal. A series of experiments was conducted in this study using Spectra Quest’s Machinery Fault Simulator (MFS) to observe the behavioral changes of the BPF and its harmonics before and after installing an obstruction nearby an axial fan. In order to incorporate the flexibility of the shaft a modification in the existing setup (MFS- LITE) has been designed and fabricated. The whole study is divided into two parts: in the first part readings were taken without considering the effect of flexibility of shaft and for performing this, the shaft of smaller length is taken; and in the second part readings were taken with a longer shaft in order to incorporate the effect of flexibility during experimentation. The result shows that the obstruction had an obvious and consistent effect on the 1BPF and 2BPF components for the axial fan rotor system. Keywords Blade-passing frequency (BPF) · Machinery Fault Simulator (MFS) · Flexibility · Fan 1 Introduction During the operation of fluid turbo-machinery, such as pumps, fans, or turbines, fluid-dynamic perturbations are produced and can lead to vibration and noise emis- sion. Typical fluid-dynamic excitations in such machines are generally associated with pure-tone (rotation frequency, blade-passing frequency) [1], and broadband frequency components. The rotation frequency is due to small misalignments, unbal- ance, or manufacturing imperfections of the impeller. The broadband phenomena are usually caused by flow turbulence and cavitation. In some cases, excitation at the S. S. Singh (B) Department of Mechanical Engineering, JECRC, Jaipur 302005, Rajasthan, India e-mail: shashank.me@jecrc.ac.in A. A. Khan Department of Mechanical Engineering, ZHCET, AMU, Aligarh 202002, Uttar Pradesh, India © Springer Nature Singapore Pte Ltd. 2021 M. Singh and Y. Rafat (eds.), Recent Developments in Acoustics, Lecture Notes in Mechanical Engineering, https://doi.org/10.1007/978-981-15-5776-7_17 185