Anatole P. Kurkov

Integrated fiber optic light probe: Measurement of static deflections in rotating turbomachinery

This paper describes the design, fabrication, and testing of an integrated fiber optic light probe system for monitoring blade tip deflections, vibrational modes, and changes in blade tip clearances in the compressor stage of rotating turbomachinery. The system comprises a set of integrated fiber optic light probes which are positioned to detect the passing blade tip at the leading and the trailing edges. In this configuration measurements of both blade vibrations and steady‐state blade deflection can be obtained from the timing information provided by each light probe, which comprises an integrated fiber optic transmitting channel and a number of high numerical aperture receiving fibers, all mounted in the same cylindrical housing. A spatial resolution of 50 μm is possible with the integrated fiber optic technology, while keeping the outer diameter below 2.5 mm. Additionally, one fiber sensor provides a capability of monitoring changes in the blade tip clearance of the order of 10 μm. Measurements from a...

Fully Suspended, Five-Axis, Three-Magnetic- Bearing Dynamic Spin Rig With Forced Excitation

A significant advancement in the dynamic spin rig (DSR), i.e., the five-axis, three-magnetic-bearing DSR, is used to perform vibration tests of turbomachinery blades and components under rotating and non-rotating conditions in a vacuum. The rig has three magnetic bearings as its critical components: two heteropolar radial active magnetic bearings and a magnetic thrust bearing. The bearing configuration allows full vertical rotor magnetic suspension along with a feedforward control feature, which enables the excitation of various modes of vibration in the bladed disk test articles. The theoretical, mechanical, electrical, and electronic aspects of the rig are discussed. Also presented are the forced-excitation results of a fully levitated, rotating and non-rotating, unbladed rotor and a fully levitated, rotating and non-rotating, bladed rotor in which a pair of blades were arranged 180° apart from each other. These tests include the “bounce” mode excitation of the rotor in which the rotor was excited at the blade natural frequency of 144 Hz. The rotor natural mode frequency of 355 Hz was discerned from the plot of acceleration versus frequency. For non-rotating blades, a blade-tip excitation amplitude of approximately 100 g A−1 was achieved at the first-bending critical (≈144 Hz) and at the first-torsional and second-bending blade modes. A blade-tip displacement of 1.778×10−3m (70 mils) was achieved at the first-bending critical by exciting the blades at a forced-excitation phase angle of 90° relative to the vertical plane containing the blades while simultaneously rotating the shaft at 3000 rpm.

Time-of-Flight Tip-Clearance Measurements

H.S. DhadwalIntegrated Fiber Optic Systems, Inc., Stony Brook, New YorkA.P. Kurkov and D.C. JanetzkeGlenn Research Center, Cleveland, OhioPrepared for the35th Joint Propulsion Conference and Exhibitsponsored by the AIAA, ASME, SAE, and ASEELos Angeles, California, June 20-24, 1999National Aeronautics andSpace AdministrationGlenn Research Center

Optical Measurements of Unducted Fan Flutter

The paper describes a nonintrusive optical method for measuring flutter vibrations in unducted fan or propeller rotors and provides detailed spectral results for two flutter modes of a scaled unducted fan. The measurements were obtained in a high-speed wind tunnel. A single-rotor and a dual-rotor counterrotating configuration of the model were tested; however, only the forward rotor of the counterrotating configuration fluttered. Conventional strain gages were used to obtain flutter frequency; optical data provided complete phase results and an indication of the flutter mode shape through the ratio of the leading- to trailing-edge flutter amplitudes near the blade tip. In the transonic regime the flutter exhibited some features that are usually associated with nonlinear vibrations. Experimental mode shape and frequencies were compared with calculated values that included centrifugal effects.Copyright

Real Time Flutter Monitoring System for Turbomachinery

A fiber optic laser probe based system is described for real time monitoring of flutter in rotating turbomachinery. The digital flutter monitoring system is designed for continuous processing of blade tip timing data at a rate of 10 MB/s. A USB2.0 interface provides un-interrupted real time processing of the data. The blade tip arrival times are measured with a 50 MHz bscillator and a 24-bit pipelined counter architecture. A graphical user interface provides on-line interrogation of any blade tip from any light probe sensor. Alternatively, data from all blades can be superimposed into a single composite scatter plot displaying the vibration amplitude of each blade. A hardware platform was developed to simulate a seventy two bladed turbine operating at 15,000 rpm. Blade tip responses from three light probes were generated in an infinite loop, providing reproducible and controlled conditions for testing the vibration monitoring system. Time interval measurements were consistently made with a single count error in a 24-bit count vector. Real time testing was done using a two blade rotor mounted in an evacuated chamber at the Spin Rig Facility at the NASA Glen Research Center. The shaft in this facility was suspended by two radial magnetic bearings and the nonsynchronous vibration was communicated to the blades through the magnetic bearing. The shaft motion was much smaller than the blade vibratory amplitude, realistically simulating flutter vibrations. Nonsynchronous vibratory amplitudes for the first mode were of the order of twenty mils and for the second mode of the order of a few mils.Copyright

Dual-Laser Probe Measurement of Blade-Tip Clearance

This paper describes two dual-laser probe integrated fiber optic systems for measuring blade tip clearance in rotating turbomachinery. The probes are nearly flush with the casing inner lining resulting in minimal flow disturbance. The two probes are closely spaced in a circumferential plane and are slanted at an angle relative to each other so that the blade tip traverse time of the space between the two laser beams varies with the tip radius allowing determination of the tip clearance at the rotor operating conditions. The tip clearance can be obtained for all the blades in a rotor with a single system, provided there are no synchronous vibrations present at a particular operating condition. These probes were installed in two holders; one provided an included angle between the probes of 20 degrees, and the other provided an included angle of 40 degrees. The two configurations were calibrated in a vacuum spin rig facility that is capable of reproducing realistic blade tip speeds.© 1998 ASME

Experimental investigation of counter-rotating propfan flutter at cruise conditions

This article presents wind-tunnel experimental flutter results, at transonic relative flows, for a 0.62-m-diam composite propfan model. A blade row that fluttered was tested alone, and with a stable aft counter-rotating blade row. The major objectives of the experiment were to study the effect of the second blade row on the row in flutter, and to investigate the flutter. Results show that the second row had a small stabilizing effect. Two distinct flutter modes were found within the operating regime of the rotor; both apparently single-degree-offreedom instabilities, associated respectively with the first and second natural blade modes. For both flutter modes, flutter boundary, frequency, nodal diameter, and blade displacement data are given. The blade displacement data, obtained with an optical method, gives an indication of the flutter mode shape at a span near the blade tip.