Tip clearance

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

Moving blade tip clearance measurement apparatus and method with moveable lens

Abstract: A laser-optical apparatus for measuring blade tip clearance, e.g. of a compressor or gas turbine, uses a laser beam, fiber optics, a light probe and electrical circuits (14, 25) for processing data from the probe, and includes a light probe (16) having a lens (17) for making parallel a light beam from the optical fiber cable (15) for illumination, a half-mirror (18) for separating illuminating light and reflected light, a movable lens (19) for adjusting focus of the light beam on the object (12), an object lens (21), and a lens (22) for collected reflected light from half-mirror (18) and directing it to an entrance to the optical fiber cable (24) which transmits received light to the light reception circuit (25). The method for measuring blade tip clearance includes focusing a parallel light beam from a laser source (14, 15) through a half-mirror (18), adjustable lens (19) and object lens (21) onto an object (12), adjusting the focus by oscillating movement of the adjustable lens, detecting the reflected light received, and determining the tip clearance from the position of the adjustable lens at the time the reflected light is at a maximum value.

Model Validation for an Active Magnetic Bearing Based Compressor Surge Control Test Rig

Abstract: In this paper, we present experimental test data for the validation of a recently introduced mathematical model for centrifugal compression systems with variable impeller axial clearances. Employing the active magnetic bearings (AMBs) of a compressor built for the experimental study of surge, the axial clearance between the impeller and the static shroud is servo controlled, and the measured variations in the compressor output flow are compared with the mathematical model. The steady state and the dynamic responses of the compression system induced by varying the impeller tip clearance are measured and compared with the theoretical predictions, and the states of the compression system in surge condition are collected and analyzed. Parameters in the compression system model, such as the Greitzer parameter B and Helmholtz frequency ω H are experimentally identified. Also, the servo dynamics of the magnetic bearing that controls the axial impeller position is determined experimentally. To further validate the mathematical model and the feasibility of using the impeller tip clearance for controlling surge, we present a design example for an active surge controller based on the derived model, and simulate the response of the compression system. This design exercise also helps us understand the possible challenges that one could face in the design and implementation of a successful surge controller.

Methods for Desensitizing Tip Clearance Effects in Turbines

Abstract: This study is an attempt to reduce the effect of the leakage vortex in axial flow turbines. A 3D Navier-Stokes CFD solver with k-e turbulence modeling was used compute the flow through an axial flow turbine with modified blade tip designs. A baseline flat tip case and three modified tip cases were simulated and the leakage flow and vortex for each was analyzed in detail. The three modified blade tip designs each involved adding a chamfer to the tip of the blade, in an attempt to diffuse the leakage flow through the gap and obstruct the leakage flow with the outer casing’s shear layer. Chamfering of the blade tip near the leading edge of the gap and across the entire gap region both failed to reduce the size and strength of the leakage vortex. By chamfering the blade tip near the trailing edge of the gap, the leakage flow inside the gap was turned toward the direction of the blade’s camber. This turning resulted in a decrease in the size and the strength of the leakage vortex and its subsequent losses, while at the same time, did not reduce the blade loading by an appreciable amount.This paper is available in color on the World Wide Web at http://navier.aero.psu.edu/∼jat/research.htmlCopyright © 2001 by ASME

Tip clearance centrifugal compressor impeller

Abstract: An impeller includes first and second impeller portions that are secured to one another. An interior cavity is formed between the first and second portions. The first impeller portion supports multiple blades. The first and second impeller portions respectively include first and second surfaces that are secured to one another near a tip of the impeller. Inlet and outlet apertures are provided in the impeller and are in communication with the inner cavity to provide a cooling flow path there through. A circumferential gap is arranged between the first and second impeller portions opposite the tip to permit relative axial movement between the first and second impeller portions during centrifugal loading of the impeller.

Active tip clearance control for shrouded gas turbine blades and related method

Abstract: A turbine bucket tip clearance control system includes a rotor assembly having a rotor supporting a plurality of axially spaced wheels, each wheel mounting an annular row of buckets, the annular row of buckets on at least one of the plurality of axially-spaced wheels having a radially outer tip shroud provided with at least one seal tooth. A stator assembly includes a radially inwardly facing, axially-stepped surface, formed with radially inner and outer seal surfaces connected by a shoulder. The stator assembly and rotor assembly are moveable axially relative to each other, enabling selective positioning of the at least one seal tooth radially opposite one of the radially inner and outer seal surfaces to thereby selectively alter a clearance gap between the at least one seal tooth and the radially inward facing axially-stepped surface.