Dr Sana Iqbal
Aerodynamicist, founder
Twelve years on car and truck aerodynamics before she built a tunnel small enough to rent by the hour.
About the tunnel
The tunnel.
An open-return tunnel in a former dye works on Pollard Street. Air is drawn in from the room, straightened, sped up, blown across you, and let go again. Gustave Eiffel built this kind in Paris in 1909, which is why it is still called Eiffel-type.
A cylinder in the smoke: vortices peel off one side, then the other. Over a huge range of speeds the rhythm barely changes (a Strouhal number of about 0.2), which is why power lines hum in the wind.
How the air is made
Five parts, 21 metres end to end. The fan is at the back, pulling, so the air reaches you clean.
- 01
Inlet and honeycomb
Air from the room passes an aluminium honeycomb and three fine screens that iron out swirl and gusts.
- 02
Contraction
The duct narrows four to one, so the air speeds up four times and what's left of the turbulence shrinks.
- 03
Test section
An open jet 2.4 m wide and 1.8 m tall, up to 60 km/h. You ride in it, on a turntable that yaws ±15°.
- 04
Collector and diffuser
The jet is caught and slowed in a widening duct, which saves the fan most of the effort.
- 05
Fan
A 90 kW fan with 12 blades pulls the air through and pushes it out into the building again.
Specifications
Numbers.
- Type
- Open return, open jet (Eiffel-type)
- Jet
- 2.4 × 1.8 m
- Speed
- 0 to 60 km/h
- Turbulence
- Under 0.5% at 40 km/h
- Balance
- Six components, logged at 1 kHz
- Repeatability
- ±0.002 m² CdA, rider runs
- Turntable
- 1.6 m, ±15° yaw
- Smoke
- Hand wand and a rake of 24 nozzles, water-based fog
The name
A strake is the corkscrew fin on a tall steel chimney. Christopher Scruton and D. E. J. Walshe found in 1957, at the National Physical Laboratory, that it breaks up the vortices that shake the chimney.
We spend our days making vortices visible so people can get rid of them. The name seemed fair. And the Reynolds number, the reason a 1:50 model in a tunnel tells the truth about a building, comes from Osborne Reynolds, who worked out the idea a mile and a half from here at Owens College, now the University of Manchester.
Who runs it
Three people. One of them is in the control room for every session.
Tom Garside
Tunnel engineer
Keeps the fan, the balance and the smoke running, and builds the models for building studies.
Ruth Adeyemi
Bike fitter, position sessions
Fits riders for comfort first, then finds out how much of that comfort they can keep at race speed.