Richard Schodl

Turbo machine tip clearance and vibration measurements using a fibre optic laser Doppler position sensor

This paper presents a novel fibre optic laser Doppler position sensor for single blade tip clearance and vibration measurements at turbo machines, which offers high temporal resolution and high position resolution simultaneously. The sensor principle is based on the generation of a measurement volume consisting of two superposed fan-like interference fringe systems with contrary fringe spacing gradients using wavelength division multiplexing. A flexible and robust measurement system with an all-passive fibre coupled measurement head has been realized employing diffractive and refractive optics. Measurements of tip clearance and rotor vibrations at a transonic centrifugal compressor performed during operation at up to 50 000 rpm (833 Hz) corresponding to 21.7 kHz blade frequency and 586 m s−1 blade tip velocity are presented. The results are in excellent agreement with those of capacitive probes. The mean uncertainty of the position measurement was around 20 µm and, thus, considerably better than for conventional tip clearance probes. Consequently, this sensor is capable of fulfilling the requirements for future active clearance control systems and has great potential for in situ and online tip clearance and vibration measurements at metallic and non-metallic turbine blades with high precision.

Recent developments and applications of quantitative laser light sheet measuring techniques in turbomachinery components

Concerning the further development of gas turbine engines, advances of the aero-thermodynamic design can be achieved most efficiently by co-operative efforts aimed at the improvement of both the numerical simulation methods and the experimental test and measurement techniques. Rapid development of numerical capability is accompanied by increasing demands on experimental data. In this context significant instrumentation research efforts are being conducted to develop the needed measurement technologies. Because of the need for reduced experimental costs planar measurement techniques have undergone a rapid pace of development. Three newly developed quantitative light sheet techniques utilizing the scattered light of tracer particles are described in this paper. First a Doppler global velocimetry (DGV) system optimized for time-averaged three component velocity measurements is presented. The system, which uses a single viewing direction in conjunction with three different illumination directions enables very accurate velocity measurements. Second a quantitative light sheet (QLS) technique for quantitative mass fraction measurements in mixing processes is treated. To apply the technique the inflow of the mixing experiment must consist at least of two separate flows, one of which can be seeded while the other remains unseeded. DGV and QLS results obtained from experimental investigation in a model combuster are presented. Third a method named tracer-based shock visualization (TSV) is described which is capable of determining the shape and structure of shock waves in transonic flows by analysing the sudden increase of flow density across a shock. Results taken in a transonic compressor are presented.

3-Component Doppler Laser-Two-Focus Velocimetry Applied to a Transonic Centrifugal Compressor

The conventional Laser-Two-Focus (L2F) method, also known as Laser Transit Anemometry (LTA), measures two components of the flow vector in the plane normal to the optical axis by measuring the time-of-flight of particles crossing the two laser beams in the probe volume. Recently a new three component system was developed, named 3C, Doppler L2F, which operates with the same confocal optical set-up as the two component L2F system, thus enabling three component measurements even under the extremely difficult conditions of limited optical accessibility as they appear for example in centrifugal compressors. The new hybrid system combines the principle of the L2F technique with the basic idea of the Doppler Global Velocimetry (DGV). The two velocity components in the plane perpendicular to the optical axis are measured by the L2F time-of-flight technique, the third velocity component in the direction of the optical axis is determined by analyzing the Doppler frequency shift of the scattered light. The system was developed with respect to an application in a transonic centrifugal compressor and designed in the shape of an optical probe shown in Fig. 1. The set-up and all important components of the 3C, Doppler L2F system are described here in detail, as well as the principle of operation and calibration of the system. Tests on a free jet demonstrate the measurement accuracy of the hybrid technique. Its successful application to a transonic centrifugal compressor was the first time that three component velocity data could be collected from a high loaded, high speed centrifugal impeller. The data are presented and discussed.

Selected applications of planar imaging velocimetry in combustion test facilities

This chapter provides an overview on the application of particle image velocimetry (PIV) and Doppler global velocimetry (DGV) in combustion test facilities that are operated at pressures of up to 10 bar. Emphasis is placed on the experimental aspects of each application rather than the interpretation of the acquired flow-field data because many of the encountered problems and chosen solution strategies are unique to this area of velocimetry application. In particular, imaging configurations, seeding techniques, data-acquisition strategies as well as pre- and postprocessing methodologies are outlined.

Doppler global velocimetry for the analysis of combustor flows

Abstract The principle of Doppler global velocimetry (DGV) and a DGV system optimized for time averaged three-component velocity measurements is described in this paper. Furthermore, the design of the different components of the DGV-system as well as the manner of its operation is presented. The volumetric, time averaged, three-component velocity distribution was acquired in the isothermal flow of a low NOx, staged combustion chamber sector from Rolls-Royce Deutschland. The combustor was developed within the German public-funded Engine 3E program. On the basis of the collected data, the complex flow phenomena in the combustor could be analyzed in detail and supported by CFD calculations. A recently developed, pulsed Nd:YAG laser now enables planar, time-averaged, three-component DGV application in combusting flow fields. Measurements were carried out in a single-nozzle, kerosene combustion chamber model, operated under atmospheric pressure. The successful measurements demonstrated the capability of DGV as a new tool for combustion research. It was possible to separately measure the gas velocity and the velocity of the fuel droplets, a promising capability of DGV for two phase flow analysis.

A planar Mie scattering visualization technique for turbo machinery application

A planar Mie scattering technique is described which allows for the systematical analysis of three-dimensional shock configurations without the need for velocity measurements. For that, small particles are added to the flow upstream of the shock and illuminated by a laser light sheet. The scattered light is captured by a CCD camera so that the position of the shock wave can be determined from the increase of the light intensity across the shock. To analyze the three-dimensional structure of a shock wave, the light sheet is moved perpendicular to the flow direction. The measurement technique is applied to both a supersonic wedge flow at Ma = 2.43 and a more complex shock wave configuration in a transonic cascade flow at Ma = 1.09. The gathered results are conclusive with Schlieren photographs, numerical simulations and surface pressure measurements. As the chosen setup allows the application to test sections with restricted optical access and a synchronization of the image capturing process with an external triggering signal, the three-dimensional shock configurations inside a transonic compressor rotor can also be visualized.