Pneumatic probes overview
A practical orientation to multi-hole pneumatic probes, when to use three, five, or seven ports; how angular calibration fits into a campaign; and where uncertainty propagation and facility transfer sit in the workflow. Start here before the 3-hole probe uncertainty note or the instrumentation & measurement theme index.
Not sure where to start? 4 places to go
Start with your question
Why visitors arrive: You are choosing or calibrating pneumatic probes and need orientation before diving into derivations.
Your question: What probe configuration fits my measurement, and what calibration workflow should I follow?
You may also be asking
- How is uncertainty propagated for a 3-hole probe?
- What is multi-facility transfer?
- Where is the Oxford open-hardware publication?
Where to go next
- 3-hole uncertainty note: Full propagation derivation
- Uncertainty fundamentals: Metrology baseline
- Experimental measurement article: Campaign traceability
- Instrumentation theme: Full resource index
Choose the probe to match the measurand
Pneumatic probes infer flow direction and pressure from differential port readings. The port count sets which velocity components you can resolve in one attitude, how nonlinear the calibration surface becomes, and how much facility transfer work you inherit when merging datasets.
- 3-hole: yaw plane + total/static recovery in 2D or axisymmetric flows, see uncertainty derivation
- 5-hole: full pitch and yaw in 3D wakes and secondary flows, see multi-facility calibration project
- Campaign discipline: experimental aerothermal measurement and uncertainty fundamentals
Probe configurations at a glance
| Configuration | Typical measurands | When it fits | Calibration burden |
|---|---|---|---|
| 3-hole (yaw plane) | Yaw angle, total pressure, static pressure in a plane | 2D cascades, pitch-averaged traverses, quick yaw surveys where pitch variation is small | Lower-dimensional polynomial surface; well suited to documented Taylor propagation |
| 5-hole | Pitch and yaw, total and static pressure in 3D flows | Secondary flows, mixed-out profiles, open-hardware benchmarking across tunnels | 2D calibration map; facility transfer and Monte Carlo often warranted |
| 7-hole / cobra | High angular range, complex attitudes | Separation, strong swirl, attitudes outside 5-hole range | Heavier calibration grid; check Reynolds and Mach similarity explicitly |
Reynolds-number and Mach-number similarity still govern whether a calibration obtained in a reference jet transfers to your rig, tie probe sizing to the dimensionless groups reference and air properties calculator before committing to hardware.
Calibration and transfer workflow
The sequence below is common across Oxford ECAT campaigns and the European 5-hole cross-calibration programme documented on this site. Facility names change; the documentation structure should not.
- Define measurands: which angles and pressures are reported, and in what coordinate frame
- Reference-jet calibration: sweep pitch/yaw through a known uniform flow; fit recovery polynomials and pressure coefficients
- In-situ checks: null readings, alignment witness, transducer drift logs
- Facility transfer: compare calibration repeatability across tunnels before merging datasets (5-hole project)
- Uncertainty budget: separate bias (polynomial fit, alignment) from precision (repeatability, tunnel unsteadiness); propagate with documented partial derivatives or Monte Carlo
- Archive: calibration files, reduction scripts, and facility metadata alongside the campaign log (HPT deterioration project)
Uncertainty and publication track
Instrument-specific derivations live in technical notes; campaign narrative lives in articles and project logs. For three-hole probes, the full bias-precision propagation with partial derivatives is in the 3-hole probe uncertainty note. If metrology vocabulary is new, read measurement uncertainty fundamentals first.
The Oxford open-hardware probe manuscript (in preparation) formalises multi-facility practice, see publications and the instrumentation theme. A planned interactive probe-uncertainty module on calculators will implement the 3-hole algebra when stable.
Related resources
- Instrumentation & measurement: thematic index for this cluster
- Measurement uncertainty fundamentals: bias, precision, propagation
- 3-hole probe uncertainty analysis: full derivation
- Multi-facility 5-hole probe cross-calibration: experimental campaign
- Experimental aerothermal measurement: traceability and similarity
- Oxford probe manuscript: formal publication track
- Technical notes hub · Engineering platform
Part of
This page sits within the broader knowledge structure on lucasrey.com:
- Engineering - Central knowledge platform - tools, curriculum, notes, and research assets.
Connected work
Related content from the same research and engineering work:
Part of Engineering
This page is part of the engineering knowledge platform on lucasrey.com.
- Engineering hub - Full knowledge platform index
- Engineering notes - Reference material and methods documentation - instrumentation and turbomachinery clusters.
- 3-hole probe uncertainty - Uncertainty propagation for multi-hole pneumatic probes.
- HPT transient thermography - Transient IR data-reduction and uncertainty workflow for ECAT turbine campaigns.
- Dimensionless groups reference - Re, Ma, Nu, Pr, Bi and similarity checklists - foundational lookup linked to curriculum modules.
- Engineering notes - Reference material and methods documentation - instrumentation and turbomachinery clusters.
- Instrumentation & measurement - Pneumatic probing, calibration transfer, and uncertainty propagation.
- Measurement uncertainty fundamentals - Bias, precision, propagation methods, and practical workflow for aerothermal metrology.
- 3-hole probe uncertainty - Uncertainty propagation for multi-hole pneumatic probes.
- Experimental aerothermal measurement - Methods article on traceability, similarity, and facility transfer - links instrumentation, curriculum, and tools.
- Projects - Selected engineering projects and outcomes.
- Publications - Peer-reviewed papers and manuscripts in preparation - research pillar with thematic hubs, project links, and structured metadata.
- Engineering calculators - Air properties (live); probe uncertainty and related tools (planned).
- Technical notes index
- Instrumentation theme
- Uncertainty fundamentals
Engineering knowledge platform
More tools, curriculum, notes, and research from the same body of work:
- Engineering - Central knowledge platform - tools, curriculum, notes, research, and applied engineering work.
Where to go from here
Ways to take this further, in the order they usually happen.
- Get air properties at your own conditions - Conductivity, viscosity, specific heat, gamma and Prandtl for dry air from a temperature alone, and density, thermal diffusivity and kinematic viscosity once you add a pressure, each beside the correlation it came from and its valid range
- The rest of the engineering work - Tools, notes and the software behind them, indexed by topic
- How an engagement is scoped - Defined remit, timeline and deliverables, and which path suits which kind of work
- Discuss a piece of technical work - Scoped advisory, aerothermal review, instrumentation design and R and D roles
I take a small number of advisory engagements alongside the doctorate.