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.

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Reference Instrumentation Calibration workflow
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

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.

Probe configurations at a glance

Three probe tips seen face on: a 3-hole probe with three ports in a row, resolving yaw with total and static pressure in a plane; a 5-hole probe with a centre port and four around it, resolving pitch and yaw in 3D; a 7-hole probe with a centre port and six around it, for high angular range and complex attitudes.PROBE TIPS, FACE ON[01]3-holeyaw, total and staticpressure, in a plane[02]5-holepitch and yaw, total andstatic pressure, in 3D[03]7-holehigh angular range,complex attitudes
PROBE TIPS, FACE ON3-holeyaw, total and staticpressure, in a plane5-holepitch and yaw, total andstatic pressure, in 3D7-holehigh angular range,complex attitudes
Port layouts, schematic. More ports resolve more of the flow, and cost more calibration.
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 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, so tie probe sizing to the dimensionless groups reference and air properties calculator before committing to hardware.

Calibration and transfer workflow

The calibration and transfer workflow: Define measurands, which angles and pressures, in which frame; Reference-jet calibration, sweep pitch and yaw, fit the polynomials; In-situ checks, nulls, alignment witness, drift logs; Facility transfer, compare repeatability across tunnels; Uncertainty budget, bias apart from precision, then propagate; Archive, calibration files, scripts and facility metadata.1Define measurandswhich angles and pressures, in which frame2Reference-jet calibrationsweep pitch and yaw, fit the polynomials3In-situ checksnulls, alignment witness, drift logs4Facility transfercompare repeatability across tunnels5Uncertainty budgetbias apart from precision, then propagate6Archivecalibration files, scripts and facility metadata
1Define measurandswhich angles and pressures, inwhich frame2Reference-jet calibrationsweep pitch and yaw, fit thepolynomials3In-situ checksnulls, alignment witness, driftlogs4Facility transfercompare repeatability acrosstunnels5Uncertainty budgetbias apart from precision, thenpropagate6Archivecalibration files, scripts andfacility metadata
The sequence common to the campaigns on this site. Facility names change; the documentation structure should not.

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.

  1. Define measurands: which angles and pressures are reported, and in what coordinate frame
  2. Reference-jet calibration: sweep pitch/yaw through a known uniform flow; fit recovery polynomials and pressure coefficients
  3. In-situ checks: null readings, alignment witness, transducer drift logs
  4. Facility transfer: compare calibration repeatability across tunnels before merging datasets (5-hole project)
  5. Uncertainty budget: separate bias (polynomial fit, alignment) from precision (repeatability, tunnel unsteadiness); propagate with documented partial derivatives or Monte Carlo
  6. 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.

About this work

Lucas Rey, aerothermal systems engineer and academic tutor.

  • University of Oxford: DPhil Researcher, Thermofluids Institute.
  • University of Cambridge: Alumnus.
  • Rolls-Royce: Sponsored researcher (High-pressure turbine programme).

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