This invention relates to rotator members for rotation with a rotating means; and, more particularly, to an airfoil member for circumferential rotation in a fluid about an axis.
Modern axial flow turbine engines, for example aircraft gas turbine engines, include rotator members for general circumferential rotation about an engine axis. Such rotator members include blading members with an airfoil, typical of which are rotating fan, compressor and turbine blades. Helicopter rotary and fixed wing aircraft propeller blades are other examples of rotator members.
Rotator members designed for use in the fan section of large aircraft gas turbine engines are examples of relatively large airfoil shaped cantilevered rotators intended to rotate in air at relatively high speeds. As is well known in the art, this results in their structure experiencing excitation from the combination of rotational speed and airflow, particularly in that half portion of the airfoil toward the airfoil outer tip. Design and manufacture of blades for such applications have been widely reported in the art, typical of which are U.S. Pat. No. 3,892,612xe2x80x94Carlson et al. (patented Jul. 1, 1975); U.S. Pat. No. 4,118,147xe2x80x94Ellis (patented Oct. 3, 1978); and U.S. Pat. No. 5,279,892xe2x80x94Baldwin et al. (patented Jan. 18, 1994).
One type of excitation of particular significance with such relatively large fan and compressor blades sometimes is referred to as stripe mode resonance. This is a vibratory mode that is a high frequency resonance phenomenon associated with wakes of airflow generated upsteam of an airfoil. Such mode, involving stress and deformation, generally is localized in the radial outer half of the airfoil, primarily in the airfoil tip region which undergoes predominantly chordwise bending. Attempts to avoid stripe mode resonance have included embedding a patch in the airfoil tip region determined to have such an occurrence, for example as shown in the above-identified Ellis patent.
Another type of detrimental airfoil excitation and vibration can occur as a result of a foreign airborne object, such as a bird, striking the airfoil during engine operation. Damage to the airfoil can cause excessive vibration not only to the engine but also to the aircraft structure. An attempt to increase airfoil chordwise stiffness and to reduce the chordwise bending and shear stress from impact has involved adding a tip cap to the airfoil. However, such a tip cap adds extra mass that can redistribute centrifugal pull force and increase spanwise stresses along the blade trailing edge near the blade""s root.
The present invention, in one form, provides a rotator member having a radial length for general circumferential rotation about an axis, a thickness and a width greater than the thickness. The member comprises a radially lengthwise inner portion extending about half of the radial length and an radial lengthwise outer portion extending about half of the radial length outwardly from the inner portion. The outer portion includes at least one corrugation extending generally along the width of the member.
In another form, the present invention provides a method for making a rotator member with widthwise stiffness by incorporating in the outer portion of the member at least one generally widthwise corrugation.