When comparing two waves, whether they are simulated results, experimental
results from a wave tank, experimental results from a field experiment
or theoretical predictions, the dimensionless parameters need to be matched.
In practice it is not possible to have all the dimensionless parameters
the same for both waves but they must be of a similar order.
The ratios 
are not particularly well matched. The relative
interface
thickness is about twelve times larger for wave (a). This should affect
the velocities near the interface, see figure 6-1. The
different interface thicknesses should have little effect on the comparison
since the experimental results are measured every 0.0125 m which is
approximately l/7.
The ratios 
are both small and of a similar size. This
means that both waves can be considered to be linear waves. The values
of 
are somewhat different for the two waves, however we are
interested in 
. For both waves this is never smaller than
0.97 in either fluid so both waves can be considered
as deep water waves. The values of f, the density ratio, are similar
for both waves giving a density difference of about 10%.
The internal Froude number [68] F
is approximately unity for both waves. This
is expected for deep waves through the dispersion relation. The
Reynolds number Re, which can be taken to be 
, is
different for both waves. The Reynolds number of wave (a), the experimental
wave, is almost thirty times the Reynolds number of wave (b), the
simulated wave. Both Reynolds numbers are however large. The Reynolds
number appears in the Navier-Stokes equation as a measure of the balance
between inertial and viscous terms. Since Re is large for both waves
we expect viscous effects to be small in both waves but slightly
larger in the simulated wave. The affect of the different Reynolds
number on the two waves can most easily be seen through the ratio
of the boundary layer thickness to the wavelength
. Wave (a) and wave (b) have
and 
respectively. Both are small, however the relative
boundary layer thickness of the
simulated waves is about five times larger. The boundary layer thickness is
considerably smaller than the spacing of the experimental results.