Document
Propulsion - Airframe Integration Flight
Test Instrumentation
Stephen Cumming Hyun Dae Kim, presenting NASA Armstrong Fight Research Center Propulsion - Airframe Integration Technical Interchange Meeting May 30 & 31, 2018
Outline
• Introduction • Current Capabilities – On - and off - surface flow measurements – On - and off - surface flow visualization – Thrust estimation • Capabilities in Development • Needed Capabilities • Concluding Thoughts Propulsion - Airframe Integration Technical Interchange Meeting
Introduction
• This presentation focuses on flight test instrumentation for flow measurements applicable to PAI – Since internal engine instrumentation is not substantially different for in - flight measurements, this area isn’t covered in detail – There are some technologies for strain measurement, e.g. Fiber Optic Strain Sensing (FOSS), that have applications for PAI, but they are not covered in detail – Not intended to cover everything currently used in the flight test environment • C urrent and potential future measurement technologies at NASA Armstrong Flight Research Center are discussed Propulsion - Airframe Integration Technical Interchange Meeting
NASA Armstrong Flight Research Center
• Mission: Advancing technology and science through flight • Vision: To fly what others only imagine • 70+ years of flight test and flight research history and experience • Located on Edwards Air Force Base • Some of the aircraft tested and flown at AFRC: – X - 15 – F - 8 Digital Fly - By - Wire – F - 8 Supercritical Wing – HL - 10 Lifting Body – X - 29 – X - 31 – F - 18 HARV – F - 16XL – X - 43A – SOFIA – X - 56 Propulsion - Airframe Integration Technical Interchange Meeting
Aerodynamics and Propulsion Branch
• Competencies include: – Aerodynamics – Propulsion and Performance – Flow Physics – Aerospace Meteorology • Responsibilities include both research and airworthiness support Propulsion - Airframe Integration Technical Interchange Meeting
Current Capabilities
• A wide variety of flight test instrumentation exists to characterize the flow in and around a propulsion system • Capabilities exist to provide flow measurements on and off of surfaces and to provide flow visualization on and off surfaces • Techniques exist to estimate as - installed thrust during flight Propulsion - Airframe Integration Technical Interchange Meeting
On - Surface Flow Measurements
• Electronic Scanned Pressure Sensors – Are used to measure a large number of relatively steady pressures – Generally installed via drilled ports or surface - mounted strip - a - tube – Due to tubing, difficult to use for dynamic pressure environments – Requires temperature control of measurement unit for reasonable accuracy in - flight • Absolute pressure sensors – Are used to measure absolute pressure at a single location – Variety of form factors and sizes provide options for drilled ports or surface mounting – Wide range of potential response rates – Temperature sensitivity can be problematic in - flight Propulsion - Airframe Integration Technical Interchange Meeting
On - Surface Flow Measurements
• Differential pressure sensors/microphones – Are used to measure differential pressure at a single location – Variety of form factors and sizes provide options for drilled ports or surface mounting – Wide range of potential response rates – Some temperature sensitivity, but not as large a concern as for absolute sensors – Location of reference pressure measurement is critical to understanding the results • Thermocouples – Provide a surface temperature when mounted on a surface – Established technology, but it can be difficult to install such that the air temperature at the surface is measured instead of the structural temperature Propulsion - Airframe Integration Technical Interchange Meeting
Off - Surface Flow Measurements
• Flow rakes – Are used to provide off - surface flow properties for a variety of geometries, including pressure, temperature, flow velocity and direction (calibration required for flow velocity and direction) – Can be designed to provide steady or dynamic measurements – Hardware must be designed for flight environment – Calibration often needed – Measured flow is affected (to various degrees) by the rake itself Propulsion - Airframe Integration Technical Interchange Meeting
Off - Surface Flow Measurements
• Multi - hole probes – Are used to provide pressure, flow velocity and direction, and sometimes temperature at a specific off - surface location – A large variety exist, ready to purchase off - the - shelf – Calibration is required – Measured flow is affected (to various degrees) by the probe itself Propulsion - Airframe Integration Technical Interchange Meeting
Inlet Rake
• Typically used for new design long inlets to characterize inlet flow characteristics. Industry standard is a 40 probe rake (8 rakes with 5 probes each) • total pressure distortion • average total recovery • Inlet mass flow (transient and steady (P2ave/P0) • vibration state) • stall margin • shock wake • acoustic phenomenon • thermal distortion determination (inlet buzz) • flow angularity Propulsion - Airframe Integration Technical Interchange Meeting
On - Surface Flow Visualization
• Oil Flow/Liquid crystal – Can identify flow direction, transition, shock locations – Minimal recent use – Techniques are messy and material can be hazardous • Sublimation chemicals/ Emitted dyes or glycol – Can identify turbulence and separated flow – Minimal recent use – Only one test point per flight – Techniques are messy Propulsion - Airframe Integration Technical Interchange Meeting
On - Surface Flow Visualization
• Tufts – Can identify flow direction and separated flow – Easy and cheap to install – Careful consideration of installation required to avoid influencing the flow – Variety of types of materials used (flow cones, parachute cord, wool yarn, etc.)
• Infrared imaging – Can be used to detect laminar, transition, and turbulent flow and shocks – Most easily used at supersonic flight conditions – Requires temperature difference – Requires specialized viewing system Propulsion - Airframe Integration Technical Interchange Meeting
Off - Surface Flow Visualization
• Smoke – Can be used to visualize vortical flow, separated flow, and streamlines – Minimal recent use – Requires substantial modifications to aircraft to use – Substantial fire hazard • Natural Condensation – Can be used to visualize vortical flow, shocks, shear layer instabilities – Minimal recent use – No modifications required to aircraft, but not reliable and difficult to repeat • Schlieren – Can be used to visualize density changes from shock structures from supersonic shocks, subsonic and supersonic vortices – Two methods currently used for flight: AirBOS and BOSCO Propulsion - Airframe Integration Technical Interchange Meeting
AirBOS
• Airborne Background Oriented Schlieren – Downward looking at desert vegetation or ocean speckles – Wide field of view, very detailed – Currently using KingAir to look down on target – Imaged F - 18, F - 15, and T - 38 – Only T - 38 releasable currently Propulsion - Airframe Integration Technical Interchange Meeting
BOSCO
• Background Oriented Schlieren using Celestial Objects – Ground based (upward) or air - to - air (side view) looking at Sun/Moon – 0.5 deg field of view – Working toward air - to - air capability Propulsion - Airframe Integration Technical Interchange Meeting
Thrust Estimation
• Extremely difficult to directly measure thrust – Previous efforts involved strain gauges on thrust links or string pots that require installed thrust stand run to calibrate • Engine model is used in conjunction with instrumentation and other information from engine to estimate thrust – Bill of Material engine sensors: N1 , N2, fuel flow, pressures, temperatures, nozzle area, guide vane positions – Engine/Airframe communication : All buss communication between engine and airframe – Performance testing requirements : Flight test quality fuel flow, fuel sample lab testing for all flights • Technique is highly reliant on accurate modeling – Generic models can have errors as large as 20% – OEM models are an improvement (errors as small as 2%), but uncertainties due instrumentation and fuel are still present Propulsion - Airframe Integration Technical Interchange Meeting
Capabilities in Development
• Low - profile conformal pressure sensors • Low - profile conformal shock and transition detection sensors • Carbon - based heating layer for laminar/turbulent flow visualization • Pressure sensitive paint (PSP) for in - flight use • Wireless sensor and instrumentation sensor technologies Propulsion - Airframe Integration Technical Interchange Meeting
Needed Capabilities
• Improved off - surface flow measurements and visualization – In - flight Particle image velocimetry (PIV ) has been targeted for future efforts, but currently unfunded • Improved flight - capable pressure sensors – Less intrusive, less temperature dependence, cost effective • Less intrusive sensors and visualization techniques • Improved engine modeling for flight test Propulsion - Airframe Integration Technical Interchange Meeting
Concluding Thoughts
• Current flight test instrumentation capabilities have been adequate for conventional aircraft configurations but have limitations, including potential for affecting flow • New and improved instrumentation may be needed to properly evaluate future configurations • NASA AFRC is continually looking for opportunities to take new flight test instrumentation to flight Propulsion - Airframe Integration Technical Interchange Meeting
Questions?
Thanks: Mark Davis James Faber Mike Frederick Daniel Jones Propulsion - Airframe Integration Technical Interchange Meeting