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Low speed aeroacoustic test of an open rotor powered complete model

Final Report Summary - LAC-LORR OTS (Low speed aeroacoustic test of an open rotor powered complete model)

Executive Summary:
In the framework of the CleanSky project designated with the acronym LAc-LoRR OTS (Proposal reference number: 326005 - Call identifier: SP1-JTI-CS-2012-02 - Topic addressed: JTI-CS-2012-2-SFWA-02-030) 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 LAc-LoRR OTS was realized in combination with its partner project LAAME-CROW. 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 and performance data were also used by the LAAME-CROW test to select the most promising 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 OTS program to optimize the selection of model components and their placement to optimize the aerodynamic performance of the USF propulsion system.

Inflow near-field and semi near-field data and out-of-flow far-field acoustic data were measured within the LAc-LoRR OTS test program. The acoustic out-of-flow data were also used to verify the acoustic results from the enhanced phased microphone array technique, which was applied within the LAAME-CROW test program.

LAc-LoRR OTS specific objectives and activities
One main objective of the LAc-LoRR OTS program was generating high quality aerodynamic performance data of the installed USF propulsion system. The other was generating of high quality aeroacoustic data, measured in the near-field, semi near-field and far-field of the USF engine and the Z08 airframe.

The aerodynamic performance data of the Z08 aircraft model was measured by means of DNW’s high quality six components internal main balance and DNW’s multi-channel steady pressure measurement system (about 400 pressures were measured by this system for this test).
The performance of the USF propeller was measured by a six components rotating shaft balance (RSB) system, provided and operated by the Topic Manager. Dynamic and steady data from the highly instrumented USF rotor blades were continuously observed, measured and processed by data acquisition systems provided by the Topic Manager.

Near-field acoustic data were measured by a large amount of ‘Kulite-type’ pressure sensors, which were installed into the surface of the USF rotor blades and by microphones, which were installed into the surface of the fuselage of the Z08 model. Semi near-field acoustic data were measured by means of a traversable inflow wing, which was instrumented with 48 inflow microphones and were provided by the Topic Manager. The near-field and semi near-field signals were measured and processed by the Topic Manager and were only used by the LAc-LoRR OTS test program.

Out-of-flow far-field acoustic data were measured by means of four axial microphone lines, which were installed outside of the open jet flow on the floor of the of the open test section. Each line was instrumented with 13 microphones. Two lines were installed on the star-board side and two lines were installed at the port-side of the Z08 model. With 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 airframe was investigated by these four microphone lines. Furthermore the out-of-flow data were used to verify the results from the phased microphone array, which was applied in the LAAME-CROW project.

Project Results:
For the successful execution of the test with the current wind tunnel model two high performance air powered engines were developed to drive the new developed high performance USF propellers. The USF propellers were highly instrumented and provided detailed performance data.

A new designed system of four acoustic observer lines was successfully applied for the first time at DNW.

Generation of data about the aerodynamic and aero-acoustic characteristics of a newly developed USF rotor and stator blade design in combination with installation effects onto a full aircraft model inclusive high-lift wing configurations. Acoustic measurements and propulsion simulations were successfully combined.

Extensive databases of aerodynamic and performance data of the USF system were measured in combination of the complex flow field caused by a full aircraft model in high-lift wing configuration. These data are highly representative for a realistic full scale propeller installed on an aircraft. The aerodynamic and performance data are of high value for validation of CFD model simulations for reliable prediction of new enhanced USF propeller systems.

Extensive databases of acoustic inflow near-field and out-of-flow far-field microphone data were generated for the assessment of the feasibility of the USF propeller technology for an energy efficient engine system with acceptable noise impact to the environment.

Potential Impact:
The test has been a substantial (and critical) intermediate step in the development of a new European of 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 for the preparation of a first flight of a 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

List of Websites:
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