Tip clearance

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

Optical fiber sensor for measuring tip clearance of rotating blades

Abstract: The utility model relates to an optical fiber sensor and in particular relates to an optical fiber sensor for measuring tip clearance of rotating blades. The optical fiber sensor comprises a probe (3) and is characterized in that the probe (3) consists of single emitting optical fiber (1) and three groups of receiving optical fiber beams (2) which are tightly arranged in a three-ring mode; the single emitting optical fiber (1) is positioned at the central position; and the three groups of receiving optical fiber beams (2) are closely arranged by taking the single emitting optical fiber (1) as a center. The optical fiber sensor adopts a three-ring type optical fiber arrangement mode so as to reduce the size of the probe (3), enlarge the linear measurement range and improves the sensitivity. The optical fiber sensor is provided with three groups of receiving optical fiber beams, can acquire three groups of light intensity signals, can reduce or even eliminate the influence of the change of the tip surface reflectivity and the change of the included angle between the tip surface and the end surface of the sensor on the measurement result by performing ratio processing on the acquired three groups of light intensity signals.

Numerical Simulation of Tip Clearance Effects in Turbomachinery

Abstract: The numerical formulation developed here includes an efficient grid generation scheme, particularly suited to computational grids for the analysis of turbulent turbomachinery flows and tip clearance flows, and a semi-implicit, pressure-based computational fluid dynamics scheme that directly includes artificial dissipation, and is applicable to both viscous and inviscid flows. The values of these artificial dissipation is optimized to achieve accuracy and convergency in the solution. The numerical model is used to investigate the structure of tip clearance flows in a turbine nozzle. The structure of leakage flow is captured accurately, including blade-to-blade variation of all three velocity components, pitch and yaw angles, losses and blade static pressures in the tip clearance region. The simulation also includes evaluation of such quantities of leakage mass flow, vortex strength, losses, dominant leakage flow regions and the spanwise extent affected by the leakage flow. It is demonstrated, through optimization of grid size and artificial dissipation, that the tip clearance flow field can be captured accurately.Copyright © 1993 by ASME

Test Rig for Evaluating Active Turbine Blade Tip Clearance Control Concepts

Abstract: Improved blade tip sealing in the high pressure compressor and high pressure turbine can provide dramatic improvements in specific fuel consumption, time-on-wing, compressor stall margin and engine efficiency as well as increased payload and mission range capabilities of both military and commercial gas turbine engines. The preliminary design of a mechanically actuated active clearance control (ACC) system for turbine blade tip clearance management is presented along with the design of a bench top test rig in which the system is to be evaluated. The ACC system utilizes mechanically actuated seal carrier segments and clearance measurement feedback to provide fast and precise active clearance control throughout engine operation. The purpose of this active clearance control system is to improve upon current case cooling methods. These systems have relatively slow response and do not use clearance measurement, thereby forcing cold build clearances to set the minimum clearances at extreme operating conditions (e.g., takeoff, re-burst) and not allowing cruise clearances to be minimized due to the possibility of throttle transients (e.g., step change in altitude). The active turbine blade tip clearance control system design presented herein will be evaluated to ensure that proper response and positional accuracy is achievable under simulated high-pressure turbine conditions. The test rig will simulate proper seal carrier pressure and temperature loading as well as the magnitudes and rates of blade tip clearance changes of an actual gas turbine engine. The results of these evaluations will be presented in future works.

Unsteady Numerical Investigation of Blade Tip Leakage, Part 2: Time-Dependent Parametric Study

Abstract: The purpose of the present work is to conduct an unsteady study of the tip leakage flow adjacent to the shroud in real gas turbine engines using an in-house industrial computational fluid dynamics code. Both time-averaged and time-dependent data for the velocity, temperature, and mass flow rate in the tip clearance region are presented in parts 1 and 2, respectively. In part 2 of the present work, the effect of tip clearance height, inlet turbulence intensity, inlet total temperature, and rotor angular velocity on the tip leakage flow pattern is investigated. It is found that the separationbubbleisalwayspresentnearthepressuresideofthebladetipatalltimesandthatitssizevarieswith flow conditions. For smaller tip clearance heights, the mass flow rate entering the tip clearance region is lower, due to the smallerarea,whichresultsinasmallerseparationbubble.Athigherstagnationtemperatures,theseparationbubble size is also reduced, due to the flow’s higher velocity, which allows the leakage flow to dominate over the bubble growth.Also,atlowerangularvelocities,theeffectoftheshroudrelativemotionisreduced,andsomoreleakage flow is allowed to enter, thereby suppressing the growth of the separation bubble.

Improvement in the stability of a turbocharger centrifugal compressor by tip leakage control

Abstract: The occurrence of surge or stall in a centrifugal compressor and the role of the tip clearance flow in the instability in the centrifugal compressor are investigated in this study. A computational method is used to study the flow field in the centrifugal compressor in order to gain a better understanding of the surge or stall mechanism. It is found that, near surge or stall conditions, the tip leakage flow at the leading edge deflects more upstream; as the deflection increases, a more severe spillage occurs which finally leads to instability of the compressor. A ring air jet injection is used to eliminate the instabilities and to extend the stable flow range of the compressor. Using an air jet injection, the stable flow range of the compressor was successfully increased with minimal decrease in the efficiency of the compressor. The effects of different injection parameters such as the mass flow, the yaw angle, the injection angle, the slot width and the slot distance on the compressor flow field are studi...