Project

FLORA (FLOw control in RAdial compressor)

Goal: The FLORA (FLOw control in RAdial compressor) project aims at promoting the development of the next generation of aeronautical engines (weight reduction, increased efficiency and stability range) to reduce environmental impact of air transport (reducing emissions of CO2, NOx and noise impact). In such a context, the compressors are major components because they determine the fuel consumption, the stability range and the acceleration ability of the entire engine. The enhancement of an engine operability involves increasing the compressor surge margin which is still an open challenge.

From an aerodynamic point of view, that requires a better understanding of phenomena which limit the stability range and to develop strategies in order to widen it while keeping (even increasing) the performance at nominal operating condition. FLORA project has two main objectives:

• First, it proposes to achieve a comprehensive understanding of the transient behaviour of the radial compressor delivered by Safran Helicopter Engines through a precise characterization of the instabilities which develop at various rotation speeds and at different Inlet Guide Vanes stagger angles. Detailed experimental investigations are planned providing an improved and time-resolved description of the path to surge (including unsteady pressure and LDV measurements).

• Then, it proposes to apply passive flow control strategies in order to push back the compressor surge line towards low mass flow which will consequently enhance the compressor stability, hence the engine operability. The project particularly aims at evaluating the benefits from the boundary layer aspiration in radial geometries in terms of performance (gain in pressure ratio and efficiency) and surge margin.

Besides experiments, calculations will help for the understanding of the internal flow structures which develop from stable operating points up to surge. Numerous (U)RANS and LES simulations will be used to get an in-depth comprehension of the impact of the flow control on the internal flow.
This project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 820099.

Methods: Laser Doppler Anemometry, RANS Equations, Large Eddy Simulation, Test rig

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Project log

Nicolas Poujol
added a research item
In centrifugal compressors, areas of reversed flow frequently develop near the endwalls at partial rotation speed. The present contribution investigates such a recirculated flow zone in an aeronautical research centrifugal compressor stage designed and built by Safran Helicopter Engines. The compressor stage is fitted with Inlet Guide Vanes (IGV). The effects of the change in the IGV stagger angle on the occurrence and development of the recirculation area is analyzed thanks to both experimental (pressure sensors) and numerical (RANS) results. The recirculation zone, born in the inducer, extends towards the hub and upstream as the compressor is throttled for the three IGV stagger angles. At high IGV stagger angle, the recirculation zone extends downstream until it reaches the impeller trailing edge. Furthermore, the impact of the onset of the recirculation on the amplitude and circumferential velocity of rotating disturbances (or instabilities) in the inducer is also described.
Pierre Duquesne
added 2 research items
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°.
Nicolas Poujol
added a research item
The flow in the vaned diffuser of an aeronautical centrifugal compressor designed by Safran Helicopter Engines is analyzed through steady and unsteady pressure measurements at different rotation speeds. The analysis leads to the identification of different operating zones thanks to a new variable, the alternate rate ?. It allows the characterization of a specific behavior of the vaned diffuser consisting of an alternate stall pattern in two adjacent channels of the diffuser. While it is close to zero at low speed, the alternate rate reaches a maximum value at a higher speed before collapsing with a further increase in the rotation speed. Depending on the value reached by the alternate rate, three distinct regimes of the flow within the diffuser can be distinguished. For low ? values, the regime is the most common one with an equivalent flow pattern in each channel of the diffuser. For moderate ? values, a mild difference of the flow fields which develop in two adjacent channels can be observed but it remains time independent. Finally, for high values of ?, the alternate pattern is amplified and becomes time dependent, pulsating together with the mild surge of the entire compressor.
Pierre Duquesne
added an update
Test Rig Picture
 
Pierre Duquesne
added an update
This report describes the test rig (ECL-B1) at the Laboratory of Fluid Mechanics and Acoustics (LMFA) at École Centrale de Lyon (ECL). FLORA experimental measurements are performed on the ECL-B1 test rig.
 
Pierre Duquesne
added an update
This project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 820099.
 
Pierre Duquesne
added a project goal
The FLORA (FLOw control in RAdial compressor) project aims at promoting the development of the next generation of aeronautical engines (weight reduction, increased efficiency and stability range) to reduce environmental impact of air transport (reducing emissions of CO2, NOx and noise impact). In such a context, the compressors are major components because they determine the fuel consumption, the stability range and the acceleration ability of the entire engine. The enhancement of an engine operability involves increasing the compressor surge margin which is still an open challenge.
From an aerodynamic point of view, that requires a better understanding of phenomena which limit the stability range and to develop strategies in order to widen it while keeping (even increasing) the performance at nominal operating condition. FLORA project has two main objectives:
• First, it proposes to achieve a comprehensive understanding of the transient behaviour of the radial compressor delivered by Safran Helicopter Engines through a precise characterization of the instabilities which develop at various rotation speeds and at different Inlet Guide Vanes stagger angles. Detailed experimental investigations are planned providing an improved and time-resolved description of the path to surge (including unsteady pressure and LDV measurements).
• Then, it proposes to apply passive flow control strategies in order to push back the compressor surge line towards low mass flow which will consequently enhance the compressor stability, hence the engine operability. The project particularly aims at evaluating the benefits from the boundary layer aspiration in radial geometries in terms of performance (gain in pressure ratio and efficiency) and surge margin.
Besides experiments, calculations will help for the understanding of the internal flow structures which develop from stable operating points up to surge. Numerous (U)RANS and LES simulations will be used to get an in-depth comprehension of the impact of the flow control on the internal flow.
This project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 820099.