Head loss in a gate plug
# Head loss in a gate plug

The following is taken from Olsen and Oldervik (1995) "Three-dimensional numerical modeling of water flow through a gate plug",
IAHR 26th. Biennial Congress, London

Today there exist several numerical models that are able to calculate the
water flow field in a general three-dimensional geometry. This study
investigates the performance of some of these models applied for a gate plug.
The gate plug case is chosen as an example from hydraulic engineering.
Physical model tests for this case exist which is used for validation of the
numerical models.

The gate plug is used in hydropower tunnels as a mean of supporting a gate.
The gate plug decreases the cross-sectional area of the tunnel, and consists of
a contraction and an expansion region. The gate is located between these
regions. Two plugs are
investigated. Plug A has a relatively long expansion region, similar to a
diffusor. For Plug B this expansion region is cut after 1/3 of the length. In
the simulated cases the plug is located in a rectangular tunnel, 7.4 m high
and 5.76 m wide. Only one quarter of the geometry is simulated, and
symmetry conditions are used on two planes. The length of the geometry is
37 meters. The inlet velocity is 1.5 m/s.

The energy loss seems reasonable for case A. For case B there
is more deviation between the calculated and observed energy loss. This can
be due to a relatively coarse grid at the cut of the expansion. The question of
number of grid cells is for many cases dependent on the speed of the
numerical model and the computers available. To check this, a new grid with
8 times as many cells were calculated for case B using SSIIM. This gave a
head loss of 2496 Pascal, a reduction in error from 73 % to 39 %.

For a geometry where the grid can be made fairly smooth, the numerical
models give a result with an accuracy of 10-20 %. For a more complex
geometry with large recirculation zones and a coarse grid the deviation
between calculated and measured head loss can be over 100 %.

Case, A; Longitudinal profile of the gate plug, where the colors show the magnitude
of the velocity.

Case A; Longitudinal profile of the gate plug, where the colors show the magnitude
of the pressure.

Case B; Longitudinal profile of the gate plug, where the colors show the magnitude
of the velocity. The number of grid cells has been increased by a factor 8.

#### This page was made by

Nils Reidar B. Olsen

Copyright © 2003, Institutt for Vassbygging, NTNU