Nodal Pattern Analysis

Abstract

The paper elucidates the manner in which impeller blades, turbine and axial compressor blades, aircraft and marine propeller blades or similar bodies, vibrate in their higher modes. It is demonstrated that complex nodal patterns derive from consistent series of simpler modes and that the frequencies of the latter may be plotted in families of curves. Classical work of Chladni, together with more recent investigations on free square and circular plates, is first reviewed. The similarity of the manner of vibration of the cantilevered plate is then described with a note on the relation of the torsional series of modes to the simple flexural “bar” type modes. The vibration nodal patterns of impeller blades are discussed and diagrams illustrate how “complex” modes were resolved into their constituent “basic” modes, each having an ordered place in the families of modes and frequencies. Similar analysis, with examples, is shown to be applicable to turbine blades, and aircraft and marine propeller blades.