F. Nurzia

3D Flow Field Measurement Around a Rotating Stall Cell

Rotating stall is an unsteady phenomenon that arises in axial and radial flow compressors. Under certain operating conditions a more or less regular cell of turbulent flow develops and propagates around the annulus at a speed lower than rotor speed. Recently little work has been devoted to the understanding of the flow field pattern inside a rotating cell. However, this knowledge could be of help in the understanding of the interaction between the cell and the surrounding flow. Such information could be extremely important during the modelling process when some hypothesis have to be made about the cell behaviour.A detailed experimental investigation has been conducted during one cell operation of an isolated low-speed axial flow compressor rotor using a slanted hot wire and an ensemble average technique based on the cell revolution time. The three flow field components have been measured on 9 axial section for 800 circumferential points and on 21 radial stations to give a complete description of the flow field upstream and downstream of the rotor. Interpretation of data can give a description of the mean flow field patterns inside and around the rotating cell.Copyright

Experimental Investigation of Stall in a Two Stage Compressor

This paper is concerned with the experimental characterisation of the unstable behaviour exhibited by a two stage axial flow compressor with variable geometry inlet guide vanes. The characterisation includes performance assessment stall transient and determination of three dimensional flow during one cell operation. The three flow components have been measured with a single slanted hot wire ensemble phase averaging technique based on several cell passages. This technique, already successfully applied for stall in an isolated rotor, is now tried on the more complex two stage compressor.Copyright

Some Considerations about the Rotating Cell Structure

Rotating stall instability in axial flow compressors arises when the mass flow is reduced at constant rotational speed. Despite the number of experimental and theoretical work already published in the scientific literature, many questions still remain unanswered. A complete model that could be of help both in the design process and in the modelling process of existing engines is not yet available. A fundamental research program has been carried out at the Department of Mechanical Engineering of the University of Cagliari with the scope of reaching a better understanding of the basic flow field structures and of the global performance in stall. The cinematic structure of the cell during abrupt full 1-cell stall in a two-stage axial flow compressor with IGV has been analysed with the aid of hot-wire anemometer and of a total pressure probe. The results have revealed interesting features about the cell flow structures and their variations along the stalled performance branch of the compressor. The present paper aims at pursuing further the flow analysis including the investigation of upstream flow field. Therefore, the inlet duct has been extended to perform the measurements. The complete flow field measurements will allow to obtain a complete cinematic description of the cell.

TIME-SPACE EVOLUTION OF SECONDARY FLOW STRUCTURES IN A TWO-STAGE LOW-SPEED TURBINE

The aim of this work is to highlight the unsteady effects related to wake-blade and blade rows interactions, but also the time-space evolution of secondary flow structures in a two-stage low-speed turbine model designed and constructed to perform unsteady measurements with different techniques [1]. In this case attention has been addressed to the analysis of the flow field in the first stage of the turbine model. Measurements are performed with aerodynamic probes downstream of the first stator and using a single slanted hot-wire anemometer downstream of the first rotor. Time-dependent relative flow field downstream of the first rotor (obtained from phase-locked averaging technique) have been reconstructed for different relative positions between stator and rotor blades. From these results the time-dependent secondary flow vectors have been obtained as well. The mean reference flow used to determine the secondary flow structure has been evaluated for each frame by mass-averaged technique. The evolution of the secondary flow structure due to the influence of the upstream and downstream stators on the first rotor has been investigated. The main unsteady effects put in evidence the variation of the intensity and spatial extension of the vortex flow structure.Copyright

Experimental Study on the Operation of an Industrial FC Fan

Centrifugal forward curved (FC) blade fans are widely used in air ventilation and conditioning and are by far the largest fan category of all. Their success is mainly due to low cost, compactness, and low noise operation. Their peak efficiency, however, falls typically in the range 50%-70%, somewhat lower than that of other centrifugal and axial fans. The vast numbers produced and sold worldwide and the cumulative effect of so many low efficiency installations raises the question of whether it is possible to enhance their efficiency. The present paper is concerned with the investigation of the three dimensional flow field in a double inlet centrifugal industrial FC fan commonly used for handling air. An open loop facility has been designed and constructed at the Department of Mechanical Engineering at Cagliari University to house, drive and test the fan. Its operation will be studied with the aid of hot-wire probes.