that designs incorporate features to assure that interior wall panels remain flat and very smooth and that the members of the structure of the convergent and divergent create minimal obstruction to air flow accordingly if the panels are made of flexible material they will include reinforcing bars that span the panel between structural members to keep them straight flat under the conditions of vacuum created by the divergent section if the panel is retracted by winding itself around a horizontal axis the bars would be positioned horizontally in the panels if the panels are retracted by winding themselves around a vertical axis they would be placed vertically in the panels if the divergent section or part of the divergent section were to be of a circular configuration rather than rectilinear the challenge of the wind shear could be addressed differently the principal challenge of wind shear and drag occurs if the wind were to strike the divergent section at right angles to the central axis of the turbine ducted tunnel this is a completely abnormal situation as the turbine is designed to follow the wind and would be a worst case situation for wind shear and drag an alternative solution for wind shear and drag would be to install aerodynamic deflectors on both sides of the circular diffuser along its horizontal centre line the deflectors would decrease the shear forces on the windward side and decrease the drag on the leeward side of the diffuser a convergent section designed using borger optimisation theory as illustrated in drawings will have an inlet surface area much smaller than the surface area of the outlet of the divergent accordingly it will be smaller in.