Tee/Wye Waterhammer Theory

The Tee/Wye junction is a static element, and its solution method is essentially the same as the Branch junction. The only difference is that the loss factors are updated dynamically similar to steady flow if the Detailed model is in full use during the transient.

Generally it is not recommended to use the detailed loss model during the transient run for multiple reasons. One is that the complexity of iterations required for the detailed tee can increase the run time. The iterations can also easily become unstable, especially in cases where the direction of the flow is changing or oscillating at the tee/wye. Additionally, the detailed tee model was not developed with the intention of calculating transient loss, so this model should be applied in the transient run with care.

In most cases, the loss at the tee is small enough that there will not be much difference between the simple and detailed models in the steady state, making it wise to just use the simple model. However, in some cases it may be required to use the detailed tee model. In that case, there are several options available on the Optional tab in the Transient K Factor section.

• Calculated - This is the default option, which dynamically updates the loss factors throughout the transient.

• Calculated but Limited - This option allows the K factor to be dynamically updated, but defines a Maximum K factor for the calculations, which may be useful in the case of large oscillations in the transient run.

• Keep Steady State Values - This option allows the loss to be calculated normally in the steady state, then behaves like a branch junction with static K factors during the transient. This may be a good assumption in the case of small changes at the tee junction.