Robin L. Elder

A high-resolution pressure-based method for compressible flows

Abstract A pressure-based procedure able to model all Mach number flows is presented. The scheme uses curvilinear coordinates and a composite low-high-order treatment with the normalized variable diagram as limiter for the convective terms. The Cartesian components of the velocity are used as dependent variables in the momentum equations and the extension of the SIMPLE method to include the compressibility effects is presented for a non-staggered grid arrangement. Comparison of the calculations with available numerical and experimental data shows that the method is accurate, self-adaptive and stable for a wide range of Mach numbers. The shock resolution is noticeably improved by using a high-order scheme for the convective term treatment.

Design considerations for a three dimensional fiber optic laser Doppler velocimeter for turbomachinery applications

Single headed three dimensional (3D) laser Doppler velocimetry (LDV) geometries generally rely upon the use of three Doppler difference channels, inclined at differing angles with respect to the mechanical axes of the probe. The transformation between the nonorthogonal measurement coordinate system and the Cartesian system can result in large errors in the calculated velocities. A theoretical analysis of the geometrically induced uncertainties in measurements produced by four single headed 3D LDV configurations is presented. These considerations have lead to the development of a single headed fiber optic 3D LDV probe based on the use of two Doppler difference channels to directly measure the transverse velocity components, and a reference beam channel to measure the on axis velocity component. The f/4 probe head has a working distance of 200 mm, designed to operate within the constraints of the limited optical access available in turbomachinery applications.

Investigation of Flow in a Radial Turbine Using Laser Anemometry

A lightweight, high pressure radial inflow turbine was tested and laser anemometry used to measure the flow at various positions within the nozzle guide vanes, immediately upstream of the rotor and at two axial stations downstream of the rotor.The laser anemometry results indicated flow conditions within the nozzle vanes which were largely two dimensional (blade-to-blade with little hub to shroud variation) except at the vane outlet. Unsteadiness due to rotor blade passing effects were detected at the nozzle guide vane trailing edge but had almost entirely decayed at the vane throat. The results also indicate significant variations in flow conditions across the pitch of the nozzles suggesting incidence variations on the rotor of approaching 30 degrees. The laser anemometry results downstream of the turbine show a swirling flow characterised by a turbulent inner core region, a ‘centre annulus’ region of uniform velocity and flow direction and an outer flow region with a similar flow direction but velocity which increases rapidly towards the outer wall. The blade passing unsteadiness (blade-to-blade) is hardly noticeable some 50mm downstream of the rotor trailing edge.Copyright

3D fiber optic laser Doppler velocimetry

Single headed 3D laser Doppler velocimetry (LDV) geometries generally rely upon the use of 3 Doppler difference channels, inclined at differing angles with respect to the mechanical axes of the probe. The transformation between the non-orthogonal measurement coordinate system and the Cartesian system can result in large errors in the calculated velocities. A theoretical analysis of the geometrically induced uncertainties in measurements produced by four single headed 3D LDV configurations is presented. These considerations have lead to the development of a single headed LDV probe based around the use of two Doppler difference channels to directly measure the transverse velocity channels, and a reference beam channel to measure the on axis velocity component. The probe may be operated in two regimes using cw radiation and wavelength division multiplexing to distinguish the three channels, or using a pulsed source and time division multiplexing.

EFFECTS OF FREE STREAM TURBULENCE ON INTERMITTENT BOUNDARY LAYER FLOWS

This paper considers the effects of free stream turbulence intensity on intermittent boundary layer flows related to turbomachinery. The present experimental investigation has been undertaken under free stream flow conditions dominated by grid generated turbulence and Reynolds numbers appropriate for turbomachinery applications. Unseparated flow transition in the boundary layer has been considered using a flat plate with the C4 leading edge which has been designed to avoid laminar separation. This configuration provided the opportunity to study the effect of a realistic turbomachinery leading edge shape on transition. Boundary layer type hot-wire probes have been used in order to acquire detailed information about the effect of the free stream conditions and the leading edge configuration on the structure of the boundary layer. Furthermore, information about the intermittency distribution throughout the boundary layer has been obtained using statistical analysis of the velocity record of the flow field.Copyright

Stage Re-Matching as a Result of Droplet Evaporation in a Compressor

An existing one dimensional stagewise compressor stability analysis programme has been extended to incorporate a model for humidity and droplet evaporation. In its modified form the model shows the extent of stage re-matching when ingesting modest amounts of water. The water distribution throughout the flow is assumed to be homogeneous. The stage interactions of an aircraft engine compressor are investigated for different environmental operating conditions. The effects of humidity on stage loading are small while the evaporation of water causes a significant shift of the operating point along the characteristics.Copyright

Study of hot flow through turbines using laser anemometry

The use of laser anemometry as a technique for flow investigation within turbomachines is now well established. Difficulties in using this technique, however, vary from machine to machine and depend upon the nature of flow involved. Various parameters such as optical access, temperature and turbulence level influence the difficulties. In this paper we explain how laser anemometry was used to investigate the flow downstream the two radial inflow turbines which variously involve such difficulties. Small radial inflow turbines have various applications in industry and are successfully used as major components of small gas turbines and turbochargers. Units were provided by american (USA) industry. Flow conditions involved in the two units were very different as one unit was operated at 400 degree(s)C inlet temperature and the other at near ambient inlet conditions but which involved subzero turbine outlet temperatures. The paper presents a comparative study of laser anemometry techniques used to measure flow in these two very different situations. Problems such as seeding, optical access have been detailed. Finally, typical results are presented.

Flow Studies using Laser Anemometry Technique in a Small Power Unit Radial Inflow Turbine

T-100 is a multipurpose small power unit developed by Sundstrand Power Systems (USA). An extensive research programme was launched for the detailed tests of the rig components including inlet protection system, Compressor stage, Combustor and the Turbine stage. Turbomachinery Group at Cranfield was involved in the study of the Turbine unit used in this programme. From the design point of view, detailed aerodynamics in these small units are of great interest especially where high velocities and narrow passages are involved. Experimental study was carried out to investigate the flow in the region between the nozzle guide vanes and the turbine rotor entry. The main concern was to find out how the nozzle guide vane flow was modified by the rotor and how the rotor flow was affected by the nozzle guide vanes. Laser measurements were taken at these positions for various flow conditions. An other area which needs considerable attention is downstream of the turbine rotor where the turning of flow and mixing process make the situation very complicated. Laser studies were undertaken in that region and to gain more confidence on laser results, a Cobra pressure probe was traversed at these stations. This paper describes various steps undertaken to obtain laser results within the machine. At the end typical laser results have been presented and discussed.

3D Fibre Optic Laser Doppler Velocimeter

In this paper the design and preliminary testing of a single headed 3D fibre optic laser Doppler velocimeter for implementation on turbomachinery rigs is described.