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Advanced Measurement Techniques in a Low Speed CROR Wind Tunnel Test

Final Report Summary - LAAME-CROW (Advanced Measurement Techniques in a Low Speed CROR Wind Tunnel Test)

Executive Summary:
In the framework of the CleanSky project designated with the acronym LAAME-CROW (Proposal reference number: 632601 - Call identifier: SP1-JTI-CS-2013-02 - Topic addressed: JTI-CS-2013-2-SFWA-02-043) low-speed aerodynamic tests were carried out on a typical A320 type passenger aircraft model, designated as the Z08 model. The tests were performed in the open 8 m x 6 m test section of the DNW-LLF low-speed wind tunnel. The Z08 model can be equipped with powered (compressed air) engine simulators, provided by Airbus to simulate the aerodynamic and aeroacoustic effects of an installed Unducted Single Fan (USF) propulsion system. The test was conducted in September/October 2016.
Project Context and Objectives:
Since 1980s with the GE36 flying test bed, significant efforts have been done until the 90s on Contra Rotating Open Rotor (CROR) development due to rising oil price. Key issues at this time were noise, vibration and structural integration.
At Clean Sky start, CROR has been considered as the best disruptive powerplant candidate thanks to its best propulsive efficiency but with a relatively low maturity level.
Risks and opportunities had to be understood before implementation onto Aircraft and first aero-acoustic, safety and certificability studies as well as physical integration trade-offs within SFWA-ITD

The CROR gate held in July 2013 concluded that Airbus is confident a CROR pusher aircraft (A/C) is feasible, including for noise certification, but its economic viability needs to be improved to become a serious alternative to conventional turbofan A/C. As a result, an “economic viability phase” ending mid-2017 was introduced to the long term CROR strategy, with potential large changes on A/C and engine definitions, including blade design. Several “techno bricks” aiming at reducing the A/C Cash Operating Cost (COC) were launched for example the alternative design of a Rear-puller A/C configuration.

In the framework of engine architecture optimization towards light weight, Safran proposed the Unducted Single Fan (USF) concept in puller configuration: it is like a CROR puller with stopped rear rotor acting as Outlet Guide Vanes (OGV) of a turbofan, i.e. as a stator. Its block fuel and COC potential was judged more attractive compared to CROR pending blade installed performance assessment and noise de-risk.

LAc-LoRR OTS & LAAME-CROW two projects combined in a complementary approach
The test program LAAME-CROW was realized in combination with its partner project LAc-LoRR OTS. Both projects were making use of the same 1:7 scale, open rotor driven single aisle large passenger aircraft model, the so-called Z08 model, which was provided by the Topic Manager (Airbus). The Z08 model is basically the same as used in the CleanSky project L-CROR-CTS (JTI-CS-2012-01-SFWA-02-028) at DNW-LLF in 2012.

Low-speed aerodynamic and aeroacoustic tests were carried out in the 8 m x 6 m open test section (OTS) of the DNW-LLF low-speed wind tunnel in the Netherlands. The Z08 model was equipped with two powered (compressed air) engine simulators, provided by the Topic Manager, to simulate and investigate the aerodynamic and aeroacoustic effects of an installed USF propulsion system. The Z08 model was mounted on a dorsal sting, located at tunnel centre line. Both tests were conducted at DNW-LLF in September/October 2016. The total test duration for both tests was 20 testing days, with 10 days for the LAc-LoRR OTS test program and the other 10 testing days for LAAME-CROW, which also included 5 days for commissioning of the Z08 model and the new USF engines.

Within the activities for the LAc-LoRR OTS test at DNW-LLF the Z08 model assembly and the overall preparations of the test setup were coordinated and realized by DNW. This included also the breakdown of the test setup in the open test section and dissembles of the Z08 model after the test.

The main objective of the LAc-LoRR OTS test was the investigation of the aerodynamic behaviour and performance of the new USF propulsion system, when installed onto a full aircraft model with realistic high-lift wing configurations. These aerodynamic data and performance data were also used by the LAAME-CROW test to select the most interesting conditions for the propeller and wind tunnel settings for the optimum application of the advanced measurements techniques used in the LAAME-CROW program.
In the complementary direction online results from the PIV measurements in the USF propeller inflow area, as realized in the LAAME-CROW program, were used for the LAc-LoRR program to optimize the selection of model components and their placement to optimize the aerodynamic performance of the USF propulsion system.

Near field acoustic data were measured by means of a traversable inflow wing, which was instrumented with 48 inflow microphones. These microphone signals were measured and processed by the Topic Manager and only used by the LAc-LoRR OTS test.

Within the LAc-LoRR-OTS program DNW’s far-field acoustic system was applied to measure on four axial lines of the test section floor, with 13 microphones per line, the far-field noise field outside of the open jet flow. Two lines were installed on the star-board side and two lines were installed at the port-side of the Z08 model. By means of these four lines the polar and lateral acoustic directivity of the starboard or port-side installed USF propulsion system could be investigated including the assessment of shielding effects of the Z08 fuselage. Also the far-field noise caused by the Z08 model was investigated by these microphone lines. The data from the LAc-LoRR program were also used by the LAAME-CROW program to verify the results measured with the phased microphone array system.

LAAME-CROW specific objectives and activities
The first main objective of the LAAME-CROW program was generating high quality aerodynamic data in the inflow area of the USF propeller and high quality aeroacoustic noise location data of the Z08 model and the USF propeller. The flow field data should be measured by means of DNW’s three components Particle Image Velocimetry (PIV) system. And the noise source localization data should be measured by DNW’s large aperture phased microphone array system.

Another important objective of the LAAME-CROW program was the realization of a dedicated commissioning program for the new engine and propeller hardware, which should be applied in the LAc-LoRR-OTS test for the first time.
Furthermore the parameters for the optimum application of the PIV measurement system and the phased microphone array system should be identified during this commissioning program.
The importance of this commissioning part is shown in the fact, that the Topic Manager had reserved about half of the total duration for LAAME-CROW the test time for the commissioning. This was about 5 days of the total 10 testing days.

Project Results:
Commisioning of the modified air-engines successful realized and optimized operational conditions for the new USF rotor and stator blades successful identified and applied for the execution of the test program.
Obtained data about the aerodynamic performance and aero-acoustic characteristics of a newly developed USF engine design in combination with the installation effects of a complete aircraft model in complex high-lift configurations. Flow field measurement by means of stereoscopic particle image velocimetry (PIV) successfully realized for several conditions of the flow field upstream of the USF front rotor. Noise source localization of USF noise and separation from airframe noise successfully realized by means of phased microphone array technique.
Combined aerodynamic performance and aero-acoustic measurements in a large low speed environment performed on a large passenger aircraft model with variations of high-lift wing configurations. Acoustic measurements and propulsion simulations are successfully combined.
Potential Impact:
The test has been a substantial (and critical) intermediate step in the development of a new European future large passenger aircraft and the design rules of USF engines installed as puller configuration at the aircraft fuselage behind the wing section. In that respect the test cleared grounds towards the preparation of a flight test aircraft.
In particular, the test aims to:
– de-risk noise certification for rear puller USF
– understand noise mechanisms and installation effects associated to rear puller USF A/C configuration

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