Scissor duct flex joint damper

A flex joint assembly includes a damper mounted to a first scissors linkage and a second scissors linkage.

BACKGROUND

The present disclosure relates to an articulated scissor duct, and more particularly to a damped scissors duct.

In some launch vehicles, in flight trajectory control is provided through steerable rocket engines. Such steerability may be achieved by interconnecting actuators to a gimbaled rocket engine. To accommodate such steerability, propellant lines may utilize flexible interconnects often known as flex joints. Such flex joints may include multiple bellows fabricated from stainless steel which can be stretched, compressed or angulated to provide the steerability required

Flex joints may be subject to unstable flow regimes in which fluids that flow along internal convolutions of the flex joint bellows may produce flow disturbances. One type of flow disturbance is flow induced vortex shedding. Flow induced vortex shedding is an unsteady flow that may occur at certain fluid flow velocities. The flow disturbances and structural response may result in feedback which may cause large displacements of the bellows convolutions and high cycle fatigue.

Usually, attempts are made to confine the flow velocity to regimes that do not have the potential to excite the bellow convolutions, but this may be difficult in systems with a highly throttleable flow.

DETAILED DESCRIPTION

FIG. 1schematically illustrates a flex joint assembly20often located within a flow line22typical of a pipe or duct system which communicates a fluid flow F. The flex joint assembly20withstands significant axial stroke such as typical in a gimbaled rocket engine R (FIG. 2). It should be understood that the flex joint assembly20may be utilized in various fluid communication systems and is not limited to rocket engines.

The flex joint assembly20generally includes a center ring assembly24, a first ring26, a second ring28, a first stabilizer linkage30, a second stabilizer linkage32and a damper34between the stabilizer linkages30,32. A first bellows36is located between the center ring assembly24and the first ring26and a second bellows38is located between the center ring assembly24and the second ring28to accommodate expansion, compression and angular movement. The center ring assembly24and stabilizing linkages30,32provide resistance to bellow system buckling or “squirm”. A torsional bellows40may be located between a first center ring42and a second center ring44of the center ring assembly24to accommodate torsional flexibility.

The stabilizer linkage30generally include a first arm46pivotally attached to the first ring26at a pivot48and a second arm50pivotally attached to the first center ring42at a pivot52. The first arm46is pivotally attached to the second arm50at a pivot54. The stabilizer linkage32likewise generally includes a first arm56pivotally attached to the second ring28at a pivot58and a second arm60pivotally attached to the second center ring44at a pivot62. The first arm56is pivotally attached to the second arm60at a pivot64. It should be understood that multiple stabilizer linkages30,32may be circumferentially located about the respective bellows36,38to provide the desired control.

The stabilizing linkages30,32advantageously provide a location to attach the damper34such as a hydraulic or mechanical damper. In the event of a flow instability (FIGS. 3 and 4) in which the center ring assembly24starts to respond to the flow due to bellows interacting with the fluid flow, the motion of the center ring assembly24(FIG. 5) will create motion in the dampers34and dissipate energy to maintain the convolution displacements of the bellows36,38under control. Each stroke of the damper34dissipates energy imparted into the system by the fluid interacting with the convolutions of the bellows36,38to significantly reduce the motion of the center ring assembly24.

The flex joint assembly20effectively damps vibration due to flow induced vibration of the fluid interacting with the bellows convolutions. The flex joint assembly20will also damp out center ring assembly24dynamic response due to engine or vehicle induced random, sinusoidal, or shock induced vibration. The load acting on the damper is a dynamic vibratory relative motion across the two linkages. This vibratory load may be provided by the motion of an automobile, train, bridge, airplane, vessel, building structure, gas pipeline, etc.