The jet fan bench thrust is reduced by deflectors
by between 5% to 20%, depending on their degree of turning, distance from the silencers and whether they are installed on one or both sides of a jet fan.
Deflectors kill the discharge swirl and this significantly extends the jet throw.
The extended jet throw can present a hazard to pedestrians and emergency responders in the tunnel, if the local air velocities are excessive (e.g. greater than 11 m/s). During traffic flow, the extended jet may cause buffeting of heavy goods vehicles, which also presents a life safety risk.
The extended jet throw from deflectors
can cause the jet to adhere to the tunnel floor or to stationary traffic (especially onto heavy good vehicles in road tunnels and trains in rail tunnels), increasing aerodynamic shear and reducing the in-tunnel thrust.
Deflector vanes cause regenerated noise
due to vibration of the vanes and vortex shedding, which can add between 1 to 3 dB to the sound power level.
Deflector vanes
can suffer from fatigue-induced failure, which could cause the vanes to fall onto the tunnel traffic, causing injury or death.
Power consumption is increased due to deflectors
by up to 12%, due to the additional pressure drop caused by the vanes.
Installation of deflectors presents an additional installation step
which costs time and money on site.
| Technology | Deflect jet | Compact | No jet throw extension | No noise regeneration | No deflector metal fatigue risk | No additional power | No loss of bench thrust | No risk of bearing damage |
|---|---|---|---|---|---|---|---|---|
| MoJet | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ |
| Conventional | ❌ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ |
| Deflectors | ✔ | ✔ | ❌ | ❌ | ❌ | ❌ | ❌ | ✔ |
| Slanted silencers | ✔ | ❌ | ✔ | ✔ | ✔ | ❌ | ❌ | ❌ |
None of these drawbacks are present with the MoJet®, which is the most modern jet fan technology available for enhancing in-tunnel thrust.
Read our technical paper on the performance of deflection vanes
Discover the benefits of the MoJet®
The reversible MoJet® tunnel ventilation system can increase the in-tunnel aerodynamic thrust by up to 100%
