Vortex Flow SuDS attenuation control

Vortex Flow Control

A vortex flow control device is commonly positioned downstream of an attenuation tank to limit the outgoing flow. The vortex flow regulator initiates a passive vortex in the body of the vortex device. This leads to a notable reduction in discharge rates compared to an equivalent diameter orifice i.e a vortex with the same inlet diameter as an orifice would pass a reduced dicharge. Alternatively the same discharge rate could be passed with a bigger inlet using a vortex device. The benefit of a bigger inlet is reduced blockage risk.

Another benefit of using a vortex device is presented in the Head-dicharge (Q-h) relationship. Vortex development consists of a number of phases. Initially there is open channel flow until the outlet opening reaches top level, this is briefly followed by orifice control; from this point there is a turbulent transition mode where a vortex initiates; followed finally with fully established vortex flow. The unique nature of this curve means that the average flow of a vortex device is higher in the range of head being considered than an orifice. The upstream storage can therefore be lower using a vortex device.

Vortex devices can be be attached to a headwall on the outlet of the SuDS basin or more typically they  are installed inside a chamber downstream of an attenuation tank/crate system. 

In order to quote for a vortex device we require: 

1. allowable discharge rate
2. head (mm)
3. outlet pipework diameter.