Test section and exhaust

The test section is the working volume of the tunnel: the place where the model sits, the laser sheet cuts, and the smoke is illuminated. The exhaust path is everything downstream of it.

Test section

Key features:

• Optical access through clear side walls for the laser sheet and for camera placement.
• A removable top for model mounting.
• A mounting plate / hardpoint on the floor of the section for sting mounts and custom fixtures.
• The pressure-ring tap for the static-ring transducer that feeds the cDAQ NI-9203 channel and supplies the Bernoulli wind-speed calculation.

Anything placed in the test section must be mechanically secure before the tunnel is started. Loose hardware becomes a projectile at the fan and a maintenance event downstream. The pre-run checklist includes a visual check of model security and a tug test on any quick-mounted fixtures — see Operations → Pre-run checklist.

Main switch

The main switch is the mains disconnect for the VFD and motor. It is mounted on the wall within reach of the computer station so the operator can kill power without moving away from the controls — this is by design and the layout must not be changed casually.

The switch operates on a closed = energized convention. The operator's view: opening the switch downward de-energizes the drive.

For lockout/tagout discipline (when the VFD enclosure must be opened), see Safety → Electrical hazards.

Exhaust path

The exhaust opens onto the back of the lab. The space immediately downstream of the exhaust is kept clear of people and obstructions. To deter people from walking into the airflow path, a parked band saw is positioned across the exit. The band saw is there as a physical barrier, not as a tool to be used; it must remain in place whenever the tunnel is energized.

The pre-run checklist confirms both: the exhaust area is clear of loose items downstream of the band saw, and the band saw is in place. If either condition is not met, the run does not start.

Why a band saw

The block exists because the lab is shared and people occasionally walk through. A rope or chain is too easy to step over; a band saw makes the path obviously impassable while still being movable when the tunnel is off and the area needs to be used for something else.

Symptoms of exhaust blockage during a run

If something restricts the exhaust during a run, the motor sees increased load and the drive current rises. The drive may trip on an overload fault (F0001 family); if so see Troubleshooting → Faults and alarms. Stop the tunnel before clearing the obstruction. Never reach into the airflow path with the motor energized.