Airfoil Cascades With Bistable
Separation Control
Author(s)
V. Tesař
Abstract
To accommodate varying flow rate and shaft speed conditions, the airfoils
arranged in cascades in hydrodynamic machines (turbines, pumps) should be
variable. Mechanical articulation is expensive and complex, reducing reliability.
The author investigated separation control by jets issuing from fixed stator
blades shaped so that the flow past them is switched by short control-jet pulses
between two alternative regimes differing in the resultant exit flow angle.
Although applicable widely, in the tests the stator cascades were mostly used in
simple rotor-less devices operating as a vortex-flow restrictor. Experiments were
supplemented by extensive numerical flowfield solutions.
Keywords: separation control, airfoil cascade, Coanda effect.
1 Introduction: the role of airfoil cascades
Cascades, the periodic systems of airfoils, e.g. Scholz [1], are essential
components of hydrodynamic machines, such as pumps or turbines. In these two
machine types, energy conversion in one direction takes place, e.g. mechanical
output is produced at the expense of decreasing hydraulic energy. The
conversion actually usually involves two cascades, a fixed stator cascade and the
other on the rotor connected with the rotating shaft. The energy transfer between
the fluid flow and the mechanical work takes place in the rotor cascade. The
stator (sometimes missing in machines that have to be cheap) either directs the
flow into the turbine rotor or, in a pump or blower, converts the kinetic energy
gained by the fluid in the rotor into the pressure rise. More complex conversions
take place in machines with a pair of rotor cascades, each on its shaft (usually
each also having its corresponding stator cascade). One of them has the role of a
Keywords
separation control, airfoil cascade, Coanda effect
Related Book
Other papers in this volume
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