Pulsation and Vibration Measurement on Stator Side for Turbocharger Turbine Blade Vibration Monitoring

Abstract

Mechanically robust turbine design with respect to blade vibration is challenging when dealing with nozzle-ring fouling and wear. Especially for engines operating with heavy fuel oil (HFO), the nozzle rings of the turbocharger turbines are prone to severe degradation in terms of contamination with unburned fuel deposits. This contamination will lead to an increased excitation of blade resonances in comparison to the nominal design. Due to the statistical character of contamination, long-term monitoring of blade vibration amplitudes would be beneficial. In the harsh environment of HFO operation, however, conventional blade vibration measurement techniques, such as those using strain gauges or blade tip timing, cannot work reliably for a long period. Thus, the objective of this research is to develop a method that enables the monitoring of turbine blades using pulsation or vibration sensors installed on the stator side. Almost a dozen turbines, both radial and axial, have been examined in order to determine a proper measurement chain/position and analytical method. Even though the challenges specific to the turbocharger turbine application—that high-frequency (up to 50 kHz) acoustic radiation from turbine blades has to be detected by a sensor on the stator side—were demanding, in the course of the investigations several clear examples of turbine blades engine-order resonance detection were gathered. Finally, the proposed method has been tested successfully in a power plant for over one year.

Effect of Mistuning and Blade Passing Frequencies on a Turbine’s Integral Mode Blade Vibration Detection Using a Pulsation Probe

“…C) displays the same trend, which is already presented in[1], but with additional information on individual blade trends. The pulsation amplitude trend along EOpuls=13, obtained by FFT and order tracking analysis, matches almost perfectly the BTT 𝑘 ̅ = −4 trace trend.…”

“…Concerning the experimental setup, refer to [1]. A piezoresistive pulsation sensor was placed approximately 1.5 times of the blade chord length away from the trailing edge on the downstream side.…”

“…A previous study [1], in addition to providing sound experimental evidence of turbocharger turbine integral mode detection using a pulsation sensor installed on the stator side away from the turbine trailing edge, also provided theoretical backgrounds, mainly based on the work conducted by [2]. During further investigations, however, it was recognized that the theories developed in the last 20 years of the 20th century, for example [2][3][4], handle mainly flutters in axial compressor stages and cannot apply directly to a turbocharger's turbine integral mode resonance.…”

“…The second topic relates to interference between classical BPFs (blade passing frequencies, pulsation peaks appearing at 𝐵 • 𝑛 𝑇𝐶 and its harmonics, with 𝐵 as blade count and 𝑛 𝑇𝐶 as rotor revolution frequency when blades are not vibrating) and the integral mode blade vibration-originating sound radiation. The low engine order fundamental mode resonance discussed in [1] or shown in Figure 1 occurs at around 70% of maximal rotor speed, at which the blade tip velocity is well below 𝑀 = 1 (M: Mach number). At a higher rotor speed, BPF airborne modes start to propagate undiminished in the axial direction, and pulsation amplitudes originating from BPFs will far exceed those coming from a blade vibration so that the detection of the blade vibration using a pulsation signal will become generally difficult.…”