During incident flow of bodies fluids such as air “stick” to the surface of the body and form the so-called boundary layer. The kind of flow within the boundary layer – laminar or turbulent – significantly affects the drag. The findings from studying the boundary layer are taken into consideration when designing aeroplanes, vessels and turbomachines.

The HM 225.02 experimental unit – used in the aerodynamics trainer HM 225 – allows the boundary layer on a flat plate to be studied. For this purpose, air flows along the plate, parallel to the surface. The plate has two different surfaces so as to study the effect of surface conditions on the boundary layer. Side bodies can be used in the measuring section. Thus the boundary layer phenomena can experience interference with a degressive or progressive pressure curve and, for example equalise the friction loss of the flow.

A horizontally movable Pitot tube, adjusted using a micrometer screw, measures the total pressures at various distances from the plate surface. The plate can be moved vertically to enable the recording of total pressures in the direction of flow. The velocity can be determined from the pressures read off the tube manometers in HM 225.

The experimental unit is attached to the HM 225 trainer, simply and precisely with quick release fasteners.