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FPGAs help Airbus juggle noise, pollution, and efficiency in open-rotor jet engines

Xilinx Employee
Xilinx Employee
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By Dave Wilson, Academic Marketing Director, National Instruments



Airbus is developing a new, innovative type of aircraft with open-rotor propulsion as part of the European Clean Sky program. Each engine uses two contra-rotating open rotors located at the tail of the aircraft and this configuration promises to increase fuel efficiency by a whopping 25%. However exposed fan blades operating at jet-engine RPMs are extremely loud, especially at takeoff, so noise abatement is also an important consideration. Airbus built a scale model of the proposed aircraft and its engines for wind-tunnel testing and asked NLR (The National Aerospace Laboratory in the Netherlands) to develop a pressure, strain, and acoustic measurement instrumentation system for the model. NLR is an independent, non-profit research institute that conducts contract research. NLR’s department of avionics technology helps develop and install instrumentation in wind tunnel test models for commercial and military aircraft and space vehicles.



Airbus Aircraft Model.jpg



Measuring and reducing propeller noise was central to this project. The wind tunnel already had an existing microphone array but these microphones were designed to measure average noise and sound pressure. This specific project needed sound-pressure measurements in relation to the angular positions of the rotating propellers and their pitches and it needed to record all of the measurements with 1 μsec or better synchronization. Sound-pressure measurements were required at many different locations to create sound distribution map or profile so NRL installed 144 microphones and pressure transducers inside the aircraft model. There are also 48 inflow microphones installed on an external traversing fixture to create a 2D sound profile plot from nearby.


In addition, Airbus needed pressure, force, and temperature data from the engine and rotating parts. Appropriate acquisition devices for these measurements that could operate in harsh conditions and the limited available space were not available on the market so NRL developed an advanced rotating telemetry system in-house. This rotating telemetry system operates wirelessly (for both power and data). Four of these wireless telemetry systems were installed in the engine rotors.



NRL Engine and Rotor Testing.jpg



Airframe and engine transducers are connected to a National Instruments (NI) 18-slot NI PXIe-1075 chassis installed inside of the aircraft model’s fuselage. The measurement system is called the Model Dynamic Measurement System. Microphones and pressure sensors were connected to the Model Dynamic Measurement system using two NI PXIe-4498 16-channel, 24-bit, high-accuracy DAQ modules and 14 NI PXIe-4331 8-channel bridge input modules.




NRL PXIe Chassis 2.jpg



NRL PXIe Chassis.jpg



An additional 8-slot NI PXI-1042 chassis filled with NI PXI-4498 modules located outside the model captures sound data from the 48 microphones on the traversing fixture and an NI DAQ module measures fixture position. This external PXI chassis acts as the master timebase for all of the acquisition modules.


A major project requirement was tight synchronization of all measurement components including the two PXI systems and the custom-built rotating acquisition systems. The NI PXI-6652 timing and control module and NI PXIe-6672 timing controller module for PXI Express were a perfect solution for synchronizing the two PXI systems but the external custom acquisition system also needed to sync with the PXI hardware, so the NRL team used NI PXI-7951R FlexRIO module to synchronize both chassis with the NLR-designed rotating telemetry systems. The NI FlexRIO module is based on a Xilinx Virtex FPGA and the FPGA-based synchronization subsystem generates phase-shifted clocks that drive all of the measurement subsystems to overcome many physical realities of the measurement system including 100m wire runs and sigma-delta A/D converter latencies.


NRL has used this measurement system for more than a year in several wind tunnels, during which it performed as expected. The system handles a Tbyte of data during each 4-minute test. Only the software has been upgraded during the course of the project.



Note: Johan de Goede and Rob Zwemmer of the National Aerospace Laboratory (NLR) in the Netherlands submitted this project to the NI Engineering Impact Awards 2014 competition. It won in the Physical Test and Monitoring category.