Numerical simulation of lee waves in the Strait of Hormuz using Delft3D model

Internal waves play an essential role in the hydrological state and energy of the oceans. One of the types of internal waves is lee waves, which are created by the passage of subsurface or tidal currents on the topography of the seabed, and are one of the factors of displacement of density layers. It is under water. This will change the amount of nutrients in the sea and the density of the sea. For this reason, the knowledge of lee waves is of great importance in the fishing and military industries. In this article, by using Delft3D three-dimensional model flow module hydrostatically and non-hydrostatically in the Strait of Hormuz, which is prone to the formation of lee waves due to its many shallows, the simulation of lee waves has been carried out and by using satellite images SAR, field data and previous studies were validated.



Two general open borders were applied to apply border conditions, one on the side of the Gulf of Oman and the other on the side of the Persian Gulf. Each of these boundaries was divided into 4 smaller boundaries for more accuracy in the simulation. In the surface layer of open boundaries, water level, water temperature and salinity have been applied, and in the vertical layers of open boundaries, water temperature and salinity have been applied. For water level, TPXO9 data, which has a spatial resolution of 1.3 degrees and a time resolution of one hour, has been used. For salinity and water temperature, data from the HYCOM model has been used, which has these data in 40 layers with resolution. A location of 0.08 degrees and a time resolution of three hours have been used. In the current 3D model, 20 layers have been used, the depth of the layers near the water surface and the crest of the obstacles is about 4 meters and in the middle layers up to 25 meters.



In the results section, the satellite image of Sentinel-1 satellites or SAR was used to verify the results. After receiving the images, radiometric and geometric corrections were applied. Then VV polarization was selected. In the results section, for further validation, the measured data of water temperature at a depth of twenty meters has been used. These data were collected by mooring method in the south of the Strait of Hormuz at coordinates 56 between February 5, 2022 and May 7, 2022 in the form of a 30-second time series.

From the examination of the wavelengths formed, it can be seen that the hydrostatic model has shown more turbulence. Also, the hydrostatic model has shown the stratification of the thermocline more accurately, so that after comparing with previous researches, this issue is well deduced.

From the examination of satellite images with vertical velocity formed in the simulation, it can be seen that both hydrostatic and non-hydrostatic models have been able to simulate the direction of propagation and generation of internal waves with an acceptable spatial approximation, with this difference that the non-hydrostatic model has larger flow velocity values, although the results of both models are in the range of -0.4 to +0.4.

Comparing the measurement data at a depth of 20 meters with the model results showed that the hydrostatic model is closer to the mooring data and was able to reconstruct the formed lee waves.