UTS FEIT Dynamics Lab vibration measurements from a rotating three-bladed fan with Simcenter Testlab

In this longer video, I demonstrate, using Siemens Simcenter Testlab, how to make meaningful measurements from a rotating, three-bladed fan. The fan is instrumented with an IEPE accelerometer (for measuring the vibration) and an IEPE tachometer (for determining the rotating speed of the fan). I also have in my armoury a modally tuned impact hammer which incorporates a force transducer. I have numerous other videos describing how to use the accel. and impact hammer for modal impact testing (primarily using Simcenter) as well as other associated tasks such as (relative) sensitivity checking and data post-processing. The focus of this video, however, is on the integration of the tachometer for completing rotating machinery testing where vibration information can be collected and processed as a function of the RPM of the rotating machine. In an earlier video (   • UTS FEIT Dynamics Lab rotating machinery s...  ), I showed the use of the tachometer for determination of the mean speed of the fan using an oscilloscope to interpret the pulsetrain which it produces. In this video, I extend on that by incorporating the accelerometer to measure vibration. I quickly noticed when starting and stopping the fan that, as for all machines which are inevitably unbalanced (this fan is quite bad, due to previous blade damage), there are rotating speeds at which the vibration is amplified. Since there is little load, the fan passes through these so-called critical speeds quite quickly when powered up but more gradually when turned off. I therefore chose to use a run-down methodology to collect frequency spectra at evenly incremented RPMs to demonstrate the phenomenon of the fan-induced forcing function coinciding with the structural natural frequencies. Firstly, however, I determine the locations of the natural frequencies of the structure using a quick modal impact measurement. Selecting a single excitation point on the fan stand with the accel. located on the opposite side, I quickly set-up and Impact Testing project and generate an FRF using in which some peaks can be readily seen. While the FRF is not as easy to interpret for this complex assembly as it would be for a beam, the COHerence function over the frequency range of interest (up to ~500 Hz) is excellent so these data are reliable. Subsequently, using Signature Testing - Advance and the tachometer to determine the rotating speed, I complete a 1250 to 100 rpm run-down with increments in RPM of 50, where the fan speed interact with the natural frequencies creating higher vibration at certain RPMs. Having collected the waterfall data with 24 FFTs therein, these are easily displayed on Waterfall and Colormap displays in post-processing within Testlab. Order cursors are plotted on the displays at 1x, 3x especially (key orders for such a system - 1x due to the unbalance and 3x due to the three blades - as well as cursors at fixed frequencies where the natural frequencies were found from the modal analysis (11, ~33 and ~153 Hz in particular). It is readily observed that the 1x is always exhibits strong vibration but that it is particularly high where it coincides with the 11 Hz natural frequency. Similarly, the 2x and 3x orders can be seen to interact with the 33 Hz natural frequency at the corresponding RPMs and so on. While this video is primarily aimed at mechanical engineering candidates on the UTS 43018 Dynamic Systems and Control B subject, it is hoped and expected that it can also be of interest and us to other vibration engineering practitioners. If it was useful to you, please like and subscribe to keep up to date with my other videos on this and other similar topics.