An Experimental and Computational Investigation of a Pulsed Air-Jet Excitation System on a Rotating Bladed Disk

Nonsynchronous vibrations are a difficult problem to address for turbomachines due to the complex nature of the forcing. Such vibrations can be caused by vortex shedding, flow instabilities, stall cells, or flutter. Testing a design with such excitations can be difficult in practice due to the required forcing. This work demonstrates an experimental excitation method using pulsed air jet excitation to create nonsynchronous vibrations in engine hardware rotating at nominal design speeds. Experimental runs were conducted to excite a number of engine orders (EOs). Blade tip timing was used to measure the blade response without interfering with the blade dynamics. The bladed disk was held at a constant rotational speed while the air jets were pulsed at a sweeping frequency to simulate rotating forcing. Computational models of the physical system were constructed using parametric reduced order models that incorporate the effects of rotational speed and small mistuning. The computational model was used in simulations that mimic the experiment; the forcing was swept across the blades while being pulsed. This results in a system response that cannot be captured using traditional harmonic analyses. The computational and experimental datasets were compared through mistuning values, amplitudes, and the nodal diameter (ND) content in the system response.