Method of controlling turbomachine blade flutter

• US 4,178,667 A
• Filed: 03/06/1978
• Issued: 12/18/1979
• Est. Priority Date: 03/06/1978
• Status: Expired due to Term

• Current Assignee: Allison Engine Company, Inc.
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Stevens, Eloy C., Swain, Kenneth
• Primary Examiner(s): Crane, Daniel C.
• Application Number:
  US05/883,688
• Time in Patent Office: 652 Days
• Field of Search: 29/156.8 B, 29/407, 73/456, 73/583, 73/147, 416/500, 416/241 R, 416/241 A, 416/241 B
• US Class Current: 29/889.2
• CPC Class Codes: F01D 5/16 for counteracting blade vibration
• CPC Class Codes: Y10S 416/50 Vibration damping features
• CPC Class Codes: Y10T 29/4932 Turbomachine making
• CPC Class Codes: Y10T 29/49774 by vibratory or oscillatory movement

Abstract

A method for controlling the first torsional node line position in a rotatable blade of a turbomachine to improve its flutter stability including the steps of forming a first monolithic blade having a desired airfoil shape with convex and concave side walls; arranging several of the monolithic blades in a cascade array and subjecting the cascade array to an unsteady, supersonic, transonic and subsonic flow condition thereacross and thereafter determining the unsteady surface pressures acting on the monolithic blades; independently determining the first torsional mode vibration node line of each of the monolithic blades and comparing the resultant unsteady pressure force on the monolithic blades and its relationship to the first torsional mode vibration node line to determine whether or not the monolithic blade is absorbing or adding energy to the air flow thereacross; thereafter forming a plurality of first and thereafter modified composite blades by adding dissimilar material to the blade shape of a monolithic blade within the confines of its convex and concave side walls with the location of the dissimilar material and the amount of the dissimilar material being determined by subjecting the first composite blades and modifications thereof to unsteady, supersonic, transonic and subsonic flow conditions while the first composite blades and modification thereof are located in a cascade array and determining the resultant unsteady surface pressures thereon and comparing such unsteady surface pressures to the location of an independently determined node line position of the first composite blades and modifications thereof so as to optimize the location of their first torsional mode node line with respect to unsteady surface pressures produced thereon under unsteady, supersonic, transonic and subsonic flow conditions so as to produce a flutter stable blade.

Claims

1. A method for controlling the first torsional node line position in a rotatable blade of a turbomachine to improve its flutter stability including the steps of:

forming a first monolithic blade having an airfoil shape with convex and concave side walls;

arranging several of the monolithic blade shapes in a cascade array and subjecting the cascade array to an unsteady flow condition and thereafter determining the unsteady surface pressure forces acting on the monolithic blades;

independently determining the first torsional node line of each of the monolithic blades and comparing the resultant surface pressure force on the monolithic blades and its relationship to the first torsional node line to determine whether or not the monolithic blade is absorbing or adding energy to the air flow thereacross;

thereafter forming a plurality of first and subsequently modified composite blades by adding dissimilar material to the blade shape of said monolithic blade within the confines of its convex and concave side walls with the location of the dissimilar material and the amount of the dissimilar material being determined by subjecting the first composite blade and modifications thereof to unsteady flow conditions while the first composite blades and modification thereof are located in a cascade array to determine the resultant unsteady surface pressures thereon and comparing such unsteady surface pressures to the location of an independently determined first torsional vibration mode node line positions of the first composite blades and modifications thereof so as to optimize the location of their first torsional vibration mode node line with respect to unsteady surface pressures produced thereon under unsteady flow conditions so as to produce a flutter stable blade.

2. A method for controlling the torsional node line location of a rotatable blade of a turbomachine to improve its flutter stability including:

forming a first monolithic blade having a root portion and an airfoil shape with convex and concave side walls thereon;

arranging several of such monolithic blade shapes in a cascade flow array and subjecting the cascade array to an unsteady condition of flow thereacross;

determining the unsteady surface pressures on the monolithic blades under the aforesaid flow conditions;

determining the torsional mode node line shape of the monolithic blade and the natural frequency of the first torsional mode vibration in the monolithic blade;

comparing the location of the aforesaid blade vibration node line with the resultant unsteady force produced by the unsteady pressure conditions on the monolithic blade to determine whether the monolithic blade is absorbing energy from or adding energy to the air flow thereacross so as to determine whether the blade is flutter stable or flutter unstable;

changing the first torsional mode vibration node line position of each of the monolithic blades in accordance with the preceding comparison by adding dissimilar material to the blade shape of the monolithic blade within the confines of its convex and concave side walls to produce a shift in the aforesaid torsional node line with respect to the leading edge of the monolithic blade to produce a first composite blade, arranging several of the first composite blades in a cascade array and subjecting them to the same unsteady supersonic and subsonic flow conditions to redetermine unsteady surface pressure acting on the first composite blade;

comparing the first torsional vibration mode node line shape and frequency of vibration of the first composite blade and the resultant force produced by the unsteady surface pressures acting on the first composite blade to determine whether or not the first composite blade is either absorbing or contributing energy to the unsteady supersonic and subsonic air flow thereacross, thereafter comparing the energy absorption level of the first monolithic blade to that of the first composite blade and readjusting the size and location of the dissimilar material on the first composite blade if it is adding energy to the air flow and thereby to produce a modified first composite blade structure, and resubjecting the modified first composite blade structure to unsteady supersonic and subsonic conditions and determining the unsteady surface pressures thereon and comparing the first torsional vibration mode node line shape and frequency of vibration of the modified first composite blade with the unsteady pressure conditions thereon to determine the energy absorbing and/or adding characteristics of the modified first composite blade so as to cause the modified first composite blade to direct energy into the air flow thereacross under unsteady supersonic and subsonic air flow conditions to produce a flutter stable blade.

3. A method for controlling the torsional node line location in a rotatable blade of a turbomachine to improve flutter stability of the blade comprising the steps of:

forming a monolithic blade having a root portion for connection to a rotor and having a desired airfoil shape with convex and concave sidewalls joined at a leading and a trailing edge, arranging the monolithic blade shapes in a cascade array, subjecting the cascade array of monolithic blades to a flow thereacross to determine unsteady pressures on individual ones of said monolithic blades, determining the natural vibration mode node line shape and frequency therein at the first natural torsional mode frequency of said monolithic blade, comparing the aforesaid blade vibration mode node line shape and frequency along with the unsteady pressure conditions of said monolithic blade to determine the amount of energy absorption by said blade in its monolithic state, producing a first composite blade and changing the node line position of said monolithic blade by adding dissimilar material to the blade shape thereof within the confines of the convex and concave sidewalls thereof, subjecting said first composite blade to an unsteady flow condition thereacross to determine unsteady surface pressures acting on said first composite blade, determining the torsional mode line shape of said first composite blade at the first torsional natural vibration mode thereof, comparing the blade vibration mode node line shape of the first composite blade with the unsteady surface pressures acting thereon and determining whether the first composite blade is either absorbing or contributing energy to the unsteady flow condition thereacross, comparing the energy absorption of the monolithic blade to that of the first composite blade and shifting the amount of dissimilar material along the chord of the monolithic blade to further shift the torsional mode node line thereof to produce a modified first composite blade, resubjecting the modified first composite blade to unsteady flow conditions to determine the unsteady surface pressures present thereon, determining and comparing the blade vibration mode node line shape and frequency of the modified first composite blade to determine whether the modified first composite blade is absorbing and/or adding energy to the flow condition thereacross until the modified first composite blade is directing energy into the flow condition thereacross under unsteady flow conditions, thereby to produce a flutter stable blade.