Computer Design for Particle Image Velocimetry

Ben Falconer

Particle Image VelocimetryUsed to measure the velocity

of a flow field cross sectionLaser creates a light sheet

through the flowCameras take quick series of

imagesCorrelation yields velocities

Multiple cross sections create a 3D map of the flow field

Image courtesy of LaVision

The ProjectSymphonyMeasure flow from a jet

engineTwo sides to project

MechanicalDigital

Focus on the digital side

RequirementsControl:

3 high resolution cameras2 lasersOne 2D traverse

Retrieve images from cameras10 images per second

Use Qinetiq’s Noise Test Facility

ProblemsObvious issues

Hostile conditionsLess obvious issues

Large amount of dataHigh acquisition rateLimited hardware

ProblemsHostile conditionsVibrations

High frequency and low frequency

Very hotAround 850K in the centre

Controlled from ~400m awayNo one is allowed in the test

chamber during experiments

ProblemsLarge amount of data

192GiB per run2048 × 2048 pixel 8 bit frames1000 double frames in each position48 positions

Cannot use conventional hard drives close to camerasToo much vibration

Currently large solid state drives (SSDs) are expensive£1150 for a 512GB SSDReasonable prices for 32-64GB SSDs

ProblemsHigh acquisition rate

Capturing frames at 10Hz40MiB/s

Maximum speed of Gigabit Ethernet is 125 MB/sOverheads reduce this to around 80MB/sToo slow to transfer multiple images simultaneously10 Gigabit exists but is extremely expensive

Hard drive speeds around 70 MB/sAgain too slow to write multiple images simultaneously

ProblemsLimited hardwarePCO cameras

Proprietary cables ~4m longInterfaces with PCI card

Hard drivesSlowVulnerable to vibration

LasersNeed local triggering

Network Design

Network DesignDriving the devices

Trigger BoxUsed to synchronise the cameras and lasersAccurate to the nanosecond scale

Solid State Based ComputersAre not affected by vibrationsCannot be far from cameras due to cable lengthDo not have capacity to store images long termAlso used to control traverse

Network Design

Network DesignStoring the data

Backup ServersRAID5 based

Redundancy Good usage of disk space ~3.5TB per server

Placed at ground level away from serious vibrationDedicated Gigabit Ethernet for each server

Only enough bandwidth for one camera’s images each

Network Design

Network DesignManaging the Network

Ethernet to each computerSeparate to data transfer lines

Control TerminalPlaced in control roomRemote desktop used to access other computersAlso used for monitoring other computers

Network Design

ResultsWorking well with single camera, SSD computer, and

backup serverWaiting for shipment of components to build full system

Questions?