Adaptation of a grid model for the generation of a prescribed full-depth atmospheric boundary layer in a wind tunnel

The Atmospheric Boundary Layer (ABL) is the lowest part of the atmosphere and its behaviour is directly influenced by turbulence. The study of its characteristics is essential for a broad spectrum of applications: wind turbines, civil engineering, marine engineering, meteorology, etc. The internship project focuses on the reproduction of a "full-depth” ABL in the wind tunnel. Multiscale Inhomogeneous Grids (MIG) and spires are used for this, which are designed in order to simulate any prescribed flows and to avoid trial-and-error approaches. The key objective is to obtain a prescribed mean velocity profile and a turbulence intensity profile representative of the real atmosphere. A theoretical model based on interacting wake turbulence is used to design the MIG grids and spires. These are produced in additive manufacturing and tested in the SCL-PIV wind tunnel at Onera Lille. The measurements are taken with both the Single Hot Wire Anemometer (S-HWA) and the Cross Hot Wire Anemometer (X-HWA). The experimental investigation showed that in order to obtain relevant findings, it is necessary to artificially simulate the Earth's surface roughness in the wind tunnel. The results proved that grids and spires are capable of reproducing a full-depth artificial boundary layer with a mean velocity profile representative of a real ABL. Moreover, these atmospheric flow generators allows to control the boundary layer height. However for all the grids, the produced turbulence intensity was insufficient for simulating the ABL. This is not valid for the spires, that generates turbulent intensity sufficiently high over the whole boundary layer height. The experimental campaign showed that the spires are the best device to reproduce an artificial ABL topped by an undisturbed freestream in the wind tunnel. Indeed, they allow to tailor accurately the mean velocity profile and to produce a turbulent intensity profile representative of the full-scale ABL.