ben falconer [email protected] supervisors: peter bryanston-cross, brenda timmerman
TRANSCRIPT
Systems for
High VelocityParticle Image Velocimetry
Supervisors: Peter Bryanston-Cross, Brenda Timmerman
Credit: AEF
• Quieter Aircraft– 96EPNdB for night takeoff/landing– Noise produced by turbulence close to engine
Why?
Credit: Steve Allen
• Turbulence produces noise– Far field noise produced close to engine– Affected by area under wing– Dependent on velocities
Far Field Noise
𝑢𝑟𝑚𝑠=√ 1𝑁 ∑𝑖=1
𝑁
(𝑢𝑖❑−𝑢)2
Turbulence strength
Number of readings
Velocity fluctuation
Particle Image Velocimetry?
Velocimetry (ˌvɛləˈsɪmɪtrɪ) n.
The measurement of the velocity of fluids
Abbreviated to PIV
• Seed flow• Illuminate• Take images• Cross correlate
How PIV Works
Credit: LaVision
• 2 Cameras• Resolves 3
components• Angle to focal
plane– Optimum θ=45°
Stereo PIV
• Focus on non-perpendicular planes• Lens held at angle
Scheimpflug Principle
• One of the largest anechoic chambers in The World– 27m x 26m
x 16m– Large scale
tests• 1:10
Noise Test Facility
Credit: QinetiQ
• No one enters during tests– Control centre 200m away
• Expensive– £10,000/hour
• Compressor– 400m/s
Noise Test Facility
Credit: QinetiQ
• Flow moving 400m/s• Can’t get close
– But particles only 0.3µm
• Remote operation• Must be fast• Full range of
distances
In Practice
• 4m x 2.6m x 4.7m• Around flightstream• 2.7m optical standoff• Mounted on 2D
traverse• Bi-directional
Full Range Rig
• Enables viewing 2 targets– For parallel planes– Preserves stereo
Mirrored Scheimpflug
• 4m x 2.6m x 4.7m• Around flightstream• 2.7m optical standoff• Mounted on 2D
traverse• Bi-directional
Full Range Rig
• Cameras moved– View under wing
• Lasers moved– Avoids wing
• Upstream• Stereo view
Wing Rig
• Hostile conditions– Vibrations kill hard drives
• Remote access• Data throughput
– Images are acquired at 60MB/s per camera– Theoretical max 125MB/s on gigabit Ethernet– 80MB/s with overheads
Computer System
• Control computer– Synchronises cameras and lasers– Accurate to nanosecond scale
• Solid statecomputers– Close to cameras– Not affected by
vibrations– Low storage capacity
Rig Computers
• Storage servers– Dedicated gigabit Ethernet each– ~3.5TB per server– Away from vibrations
Control Room
• 2 Control computers– 1 or 2 person operation– Calculate 880,000 run parameters– Organise 40TB of resulting data
Control Room
• Velocity maps–Time averaged
Results
• Turbulent kinetic energy– Indicates variation in velocity
• Closest measurement to actual acoustics
Results
𝐸𝑘=12
((𝑢1′ )2+(𝑢2′ )2+(𝑢3′ )
2)
Velocity fluctuation
Questions?
• Correlation between axes
• Can be extended to rotation
What’s Next?
• Out of plane rotation
What’s Next?
Computer System
Computer System
• Additions to base system– Mirrors– Focusing– CCTV– Remote
power
• 880,000 measurements– 1100 measurements per position– 20 positions per condition– 40 conditions
• 40TB of data– 3 Cameras– 16MB per image– 880,000 measurements
Configurations