Open rotor test capabilities
The S1MA wind tunnel is an ONERA facility, with unique features to meet the needs of Contra-Rotating Open Rotor (CROR) testing over the entire flight domain :
- 8m diameter test section
- possibility to test rotors with a diameter of about 800/900 mm (typically 1/5th scale)
- significant high pressure air capability (for air turbine simulation of the engines)
- the facility power available (up to 88 MW) allows us to explore the whole speed range of current civil aircraft up to Mach 0.97.
Taking advantage of these benefits, the BHCR (*) test bench, property of ONERA, is dedicated to CROR investigations, and has been developed for isolated configuration testing with installed configuration testing under development.
(*) BHCR: Banc pour Hélices Contra-Rotatives
ONERA provides its clients wishing to study this type of propulsion, the air turbine to drive the rotors, a high performance data acquisition system, rotating shaft balances, and the testing services for cost-effective use of the bench. The client supplies the CROR model, namely the contra-rotating rotors and spinners. ONERA design offices support the design/manufacture of the interface parts necessary for the final assembly. ONERA can also design/manufacture the model itself (propellers, hub) based on client's geometry.
Test objectives in S1MA
- Aerodynamic performance studies,
- Aero-acoustic performance studies,
- Characterisation and optimisation of the contra-rotating rotor (blade shape, number of blades, etc.)
- Evaluation of the layout architecture
- Study of installation effects
Various developments have been or are being carried out to develop the means and methods of making measurements, to increase the value of CROR tests:
Rotating shaft balance
For each rotor, a specific rotating shaft balance needs to be integrated by ONERA, to measure the forces and moments acting on the rotor. The challenges for these rotating shaft balances are:
- Need to be compact (small space available in the bench to accommodate the balance)
- Strong coupling between the six components
- Capacity to support the additional stresses associated with centrifugal forces
- Capacity to support potential out of balance loads (e.g., due to a broken blade)
In the case of a contra-rotating rotors (CROR), the two rotors are strongly interacting. To accurately measure the different interactions, we need to analyse the synchronous measurements of the harmonics : Synchronous with the front rotor (F1), synchronous with the rear rotor (F2), synchronous with rotor pair harmonic (F1 + F2 ), etc. Rather than multiplying synchronous recordings of different harmonics, ONERA has developed a method, which allows to extract the different harmonics from a single data set made at high frequency and unsynchronized with the rotors. This method has been validated on a rotating test bench by ONERA.
Data acquisition system
Large number of channels (128 "front rotor" rotating channels + 128 "rear rotor" rotating channels + 128 fixed channels) with a 30kHz bandwidth, a 62.5 kHz digitalisation frequency, a data flow of 200 Mbits/sec on the rotating parts, and of 300 Mbits/sec on the fixed parts. The system provides a resolution of 16 bits on the rotating parts and 24 bits on the fixed parts.
ONERA has available several antennas, an acoustic beam, associated data acquisition systems, and methods of signal analyses (recent developments and procurements made between 2010 and 2013), which allow to perform acoustic measurements in the near-field and far-field using a classic solid-walled test section (with no acoustic lining), which maintains the excellent aerodynamic characteristics of the wind tunnel for the CROR test in the whole operating envelope (from low speed to high transonic).
Blade deformation measurement
Adaptation of our validated method used on aircraft models. Marker dots are stuck to the rotor blades, and are viewed by two cameras. Once the cameras are calibrated, a stereography technique allows to determine the exact location of each marker frozen, which reveals blade deformations (bending and twisting).
Location of the boundary layer transition on the blades
This is achieved using an infrared camera. See also "Measurement methods>Transition tripping and vizualization" section to have more details on this technique.
The BHCR has proven to be operational in 2013 with several commercial tests being performed.
Thanks to the implementation of the BHCR bench in S1MA, the aerospace industry has now available a unique testing capability. The S1MA wind tunnel has asserted itself as a reference for the measurement of aerodynamic and acoustic datas at both low- and high-speeds for Open-Rotor configurations.