Tip clearance

About: Tip clearance is a research topic. Over the lifetime, 2637 publications have been published within this topic receiving 32671 citations.

Experimental Investigation of Centrifugal Compressor Stabilization Techniques

Abstract: Results from a series of experiments to investigate techniques for extending the stable flow range of a centrifugal compressor are reported. The research was conducted in a high-speed centrifugal compressor at the NASA Glenn Research Center. The stabilizing effect of steadily flowing air-streams injected into the vaneless region of a vane-island diffuser through the shroud surface is described. Parametric variations of injection angle, injection flow rate, number of injectors, injector spacing, and injection versus bleed were investigated for a range of impeller speeds and tip clearances. Both the compressor discharge and an external source were used for the injection air supply. The stabilizing effect of flow obstructions created by tubes that were inserted into the diffuser vaneless space through the shroud was also investigated. Tube immersion into the vaneless space was varied in the flow obstruction experiments. Results from testing done at impeller design speed and tip clearance are presented. Surge margin improved by 1.7 points using injection air that was supplied from within the compressor. Externally supplied injection air was used to return the compressor to stable operation after being throttled into surge. The tubes, which were capped to prevent mass flux, provided 9.3 points of additional surge margin over the baseline surge margin of 11.7 points.

Deterioration of Compressor Performance Due to Tip Clearance of Centrifugal Impellers

Abstract: The authors’ theory on the tip-clearance loss of centrifugal impellers is modified to include the variation of slip coefficient of the impeller due to the tip clearance, by deriving a rational relationship between two empirical parameters in the theory. In order to compare experimental data in the literature with prediction, examination was made regarding accuracy of available data and the way to select corresponding flow rates of a compressor with different values of tip clearance. Good agreement between data and prediction was observed. These examples demonstrate the following tendency regarding effects of various parameters on the tip clearance loss. Efficiency drop due to the tip clearance of high-pressure-ratio compressors is less than that of low-pressure-ratio compressors if the tip clearance ratio at the impeller exit is equal. The magnitude of clearance loss becomes smaller as the flow rate is reduced and also at a reduced shaft speed in cases of high-pressure-ratio compressors. The equations in the theory clearly show these tendencies.

Turbomachine with active tip-clearance control

Abstract: A turbomachine (10) including a case (12), a rotor (44), a plurality of rotor blades (56,58) on the rotor (44), each having a blade tip (60), a shroud (16) around the rotor blade tips (60), and bearing means (64,66) mounting the rotor (44) on the case (12) for rotation about a centreline (22) of the case (12) and for bodily-shiftable movement in the direction of the centreline (22). The rotor blade tips (60) and an inside wall (32) of the shroud (16) flare radially outwards in the direction of the centreline (22) so that, when the rotor (44) moves in the direction of the centreline (22) towards the shroud (16), a clearance gap (62) between the blade tips (60) and the inner wall (32) of the shroud (16) decreases and vice versa. An electromagnetic actuator (100) on the case (12) magnetically attracts a thrust plate (94) on the rotor (44) against a net dynamic force produced on the rotor (44) during the operation of the turbomachine (10). A control system (118) of the actuator (100) controls the magnetic attraction of the actuator (100) in response to signals from a position sensor (116) measuring the actual magnitude of the clearance gap (62), so as to maintain the actual clearance gap (62) at a predetermined magnitude.

Influence of T-shape tip clearance on performance of a mixed-flow pump:

Abstract: Influence of original and T-shape blade end on performance of a mixed-flow pump is investigated by using experimental measurement and numerical simulation. The new proposed T-shape blade end is for...

Aircraft gas turbine engine blade tip clearance control

Abstract: A method and system adjusts blade tip clearance between rotating aircraft gas turbine engine blade tips and a surrounding shroud in anticipation of and before an engine command that changes an engine rotational speed. The method may include determining when to begin adjusting the tip clearance by expanding or contracting the shroud before the engine command and may be based on monitored aircraft and/or aircraft crew data indicative of the engine. The aircraft and/or aircraft crew data may include communications between aircraft crew and air traffic control authorities or air traffic control surrogates. Determining when to begin adjusting the tip clearance may include using learning algorithms which may use the aircraft gas turbine engine's operating experience and/or operating experience of other jet engines on an aircraft containing the aircraft gas turbine engine and/or on other aircraft.