model's vertical and horizontal length scales are the same...in other words the
model is "geometrically similar."
Undistorted physical models can accurately reproduce the macro-scale
features of turbulent processes, and these physical models are the preferred tools
for studying turbulence-influenced flows provided the region of interest is small
enough and the modeling facility is large enough to accommodate undistorted
Froude scaling. When undistorted models are not feasible because of area
restrictions, an alternative might be a geometrically distorted physical model,
provided the flow conditions meet the necessary criteria.
Geometrically Distorted Models
In the context of free-surface hydrodynamic physical models, a
"geometrically distorted" model is a physical model having a vertical length
scale that is different than the horizontal length scale. Geometric distortion,
in general, invalidates the necessary scaling criteria; but under very specific
conditions the impact of geometric distortion is minimized to the point that
model results can be reliably scaled to prototype dimensions. Specifically,
situations where the vertical components of flow velocities and accelerations
are very small in comparison to the horizontal components can be modeled in
distorted models (Hughes 1993). This implies that water pressure is hydrostatic
throughout the inviscid flow region. Flow conditions that meet this specific
criterion include "long-wave models" (tidal flows) and unidirectional flow
models. However, there are certain restrictions that must be observed.
The main advantage of geometrically distorted physical models is the
flexibility in choosing the horizontal scale so that large horizontal areas can
be modeled in existing model facilities. Without geometric distortion, model
water depths would be very small, and model results could be severely affected