Jet Fan Installation Factor Calculations
About our calculator
Design your longitudinal tunnel ventilation system with the help of our free online calculator. The jet fan installation factor is a ratio of the actual to the theoretical in-tunnel thrust. We have developed our correlations for the jet fan installation factors from over 1,000 CFD calculations, and confirmed them based on full-scale tunnel tests. The results here are suitable for a first estimate of the expected jet fan thrust in a tunnel. For more details on our methodology, please have a look at our published paper.
Where can I get additional help?
If you have a tunnel project where you are considering specifying or using MoJets, please contact us.
Should the last jet fan in the streamwise direction be treated differently?
It is possible that the flow from the last jet fan in the streamwise direction does not fully mix out with the tunnel air before the exit portal, leading to a lower effective thrust. This risk is particularly high with conventional jet fans, whose discharge jets can stick to tunnel surfaces and thus entrain tunnel air only gradually. You can obtain a rough estimate of this effect by varying the jet fan spacing in the calculator.
Should the first jet fan in the streamwise direction be treated differently?
The first jet fan in the streamwise direction will not be ingesting a jet from an upstream jet fan, and should therefore have a higher installation factor than the other (“inner”) jet fans. For sake of conservatism, we normally ignore this effect, and apply the installation factor for the “inner” jet fans to all jet fans in a tunnel. If you wish to treat the first jet fan differently, you may enter a large value for the fan spacing (e.g. 1000 m).