Effects of Inlet Guide Vanes on the Performance and Stability of an Aeronautical Centrifugal Compressor

Abstract

A research centrifugal compressor stage designed and built by Safran Helicopter Engines is tested at 3 IGV (Inlet Guide Vanes) stagger angles. The methodology for calculating the performance is detailed, including the consideration of humidity in order to minimize errors related in particular to operating atmospheric conditions. The shift of the surge line towards lower mass flow rate as the IGV stagger angle increases highly depends on the rotation speed. The surge line shift is very small at low rotation speeds whereas it significantly increases at high rotation speeds. A first-order stability analysis of the impeller and diffuser sub-components shows that the diffuser (resp. impeller) is the first unstable component at low (resp. high) rotation speeds. This situation is unaltered by increasing the IGV stagger angle. At low rotation speeds below a given mass flow rate, rotating instabilities at the impeller inlet are detected at zero IGV stagger angle. Their occurrence is conditioned by the relative flow angle at the tip of the leading edge of the impeller. As the IGV stagger angle increases, the mass flow decreases to maintain a given inlet flow angle. Therefore, the onset of the rotating instabilities is delayed towards lower mass flow rates. At high rotation speeds, the absolute flow angle at the diffuser inlet near surge decreases as the IGV stagger angle increases. As a result, the flow is highly alternate over two adjacent channels of the radial diffuser beyond the surge line at IGV stagger angle of 0°.

Unsteady Analysis of a Pulsating Alternate Flow Pattern in a Radial Vaned Diffuser

“…Figure 6 shows the total-to-static pressure ratio π t−s C , the steady alternate rate A, and the unsteady alternate rate standard deviation σ A(t) as functions of the standard mass flow rate ṁstd at three IGV stagger angles: 0 • , 20 • , and 40 • . The differences in choked mass flow between the IGV stagger angles have been discussed in previous work [8]. The shape of the characteristic curves is similar at the three IGV stagger angles; the pressure ratio decreases by a few operating points before surge.…”

“…The test rig is extensively instrumented; 130 steady sensors (temperature and pressure) are used for the monitoring and the performance measurements and 52 unsteady pressure sensors manufactured by Kulite Semiconductor Product, Inc. are embedded in the shroud and in the hub at different locations. More details on the experimental setup can be found in [4,8].…”

An Open–Closed Flow Separation in a Compressor Radial Diffuser

“…In the framework of the European project FLORA (FLOw control in RAdial compressor), the compressor flow field is investigated with experimental and numerical methods [9]. The purpose of the project is to investigate aerodynamic phenomena limiting the compressor operating range and to test control methods aimed at extending this range.…”