Flow stall is an uncontrolled imbalance in the processes of laminar and turbulent nature in the movement of a gas (liquid) relative to a streamlined body.
As a rule, flow stall refers to a more particular case of a sharp increase in the turbulent component of the flow when the relative velocity threshold for the streamlined body and medium is exceeded. In any flow process, laminar and turbulent components are simultaneously present, however, in many aggregates turbulent flows are extremely undesirable, since they tend to significantly increase the load on the streamlined body, up to its destruction. In order to reduce the likelihood of stalling the flow, flow objects are given a streamlined shape .
In Aviation
In horizontal flight, turbulent flows are insignificant, occur at the point of separation of the flow, which coincides with the trailing edge of the wing of the aircraft and quickly die out. With cabling, the angle of attack increases and turbulence increases. When the critical angle of attack is reached, the flow separation point shifts along the upper surface of the wing to the leading edge, as a result of which the lifting force drops sharply, and, if the crew acts improperly, stalling occurs, which most likely turns into a tailspin . In civil aviation, this situation is considered emergency and for each aircraft , techniques for exiting the stall mode are described. At the same time, military aircraft have an increased margin of safety and thrust-to-weight ratio , which allows you to continue controlled flight at supercritical angles of attack. This opportunity underlies some aerobatics .
When landing, the plane moves at low speed and with a decrease - that is, with very large angles of attack. To tighten the stall, slit flaps are used, which allow air to flow from the lower surface of the wing to the upper.
To a lesser extent, this phenomenon is also affected by all other working planes of the aircraft: plumage , screws , turbine engine blades .
Often, the stall of a stream is erroneously called the effect of the appearance of a cloud around an airplane due to the Prandtl-Glauert singularity . Conversely, the Prantdle-Gloert Effect is called stall.
See also
- Surge (aviation)
- Cobra (aerobatics)
- Screw pitch
- Plane crash near Donetsk August 22, 2006