Tip clearance

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

Experimental and Numerical Investigation on the Tip Leakage Vortex Cavitation in an Axial Flow Pump with Different Tip Clearances

Abstract: The tip gap existing between the blade tip and casing can give rise to tip leakage flow and interfere with the main flow, which causes unstable flow characteristics and intricate vortex in the passage. Investigation on the tip clearance effect is of great important due to its extensive applications in the rotating component of pumps. In this study, a scaling axial flow pump used in a south-north water diversion project with different sizes of tip clearances was employed to study the tip clearance effect on tip leakage vortex (TLV) characteristics. This analysis is based on a modified turbulence model. Validations were carried out using a high-speed photography technique. The tip clearance effect on the generation and evolution of TLV was investigated through the mean velocity, pressure, and vorticity fields. Results show that there are two kinds of TLV structures in the tip region. Accompanied by tip clearance increasing, the viscous loss in the tip area of the axial flow pump increases. Furthermore, the tip clearance effect on pressure distribution in the blade passage is discussed. Beyond that, the tip clearance effect on vortex core pressure and cavitation is studied.

Modeling and Validation of the Thermal Effects on Gas Turbine Transients

Abstract: Secondary effects, such as heat transfer from fluid to engine structure and the resulting changes in tip and seal clearances affect component performance and stability. A tip clearance model to be used in transient synthesis codes has been developed. The tip clearance model is derived as a state space structure. The model parameters have been identified from thermo-mechanical finite element models. The model calculates symmetric rotor tip clearance changes in the turbo-machinery and symmetric seal clearance changes in the secondary air system for engine transients within the entire flight envelope. The resulting changes in efficiency, capacity and cooling air flows are fed into the performance program. Corrections for tip clearance changes on the component characteristics are derived from rig tests. The effect of seal clearance changes on the secondary air system is derived using sophisticated air system models. The clearance model is validated against FE thermo-mechanical models. The modeling method of modifying the component characteristics is verified comparing engine simulation and test data which show good agreement. Based on a representative transient maneuver typical transient overshoots in fuel flow and turbine gas temperature and changes in component stability margins can be shown. With the use of this model in the performance synthesis the transient engine performance can be predicted more accurate than currently in the engine development program.Copyright © 2004 by ASME

Online monitoring of dynamic tip clearance of turbine blades in high temperature environments

Abstract: Minimized tip clearance reduces the gas leakage over turbine blade tips and improves the thrust and efficiency of turbomachinery. An accurate tip clearance sensor, measuring the dynamic clearances between blade tips and the turbine case, is a critical component for tip clearance control. This paper presents a robust inductive tip clearance sensor capable of monitoring dynamic tip clearances of turbine machines in high-temperature environments and at high rotational speeds. The sensor can also self-sense the temperature at a blade tip in situ such that temperature effect on tip clearance measurement can be estimated and compensated. To evaluate the sensor's performance, the sensor was tested for measuring the tip clearances of turbine blades under various working temperatures ranging from 700 K to 1300 K and at turbine rotational speeds ranging from 3000 to 10 000 rpm. The blade tip clearance was varied from 50 to 2000 µm. The experiment results proved that the sensor can accurately measure the blade tip clearances with a temporal resolution of 10 µm. The capability of accurately measuring the tip clearances at high temperatures (~1300 K) and high turbine rotation speeds (~30 000 rpm), along with its compact size, makes it promising for online monitoring and active control of blade tip clearances of high-temperature turbomachinery.

Effect of Tip Clearance on Rotating Stall in a Mixed-Flow Pump

Abstract: The non-uniform disturbance in the circumferential direction is the main cause for the occurrence of rotating stall in turbomachinery. In order to study the effect of tip clearance leakage flow on rotating stall, the mixed-flow pump models with different tip clearances are numerically simulated, and then the energy performance curves and internal flow structures are obtained and compared. The results show that the computed pump efficiency and the internal flow field of the pump from numerical simulation are in good agreement with the experimental results. A saddle region appears in the energy performance curves of the three tip clearances, and with decrease in tip clearance, the head and efficiency of the mixed-flow pump increase and the critical stall point shifts, and the stable operating range of the mixed-flow pump decreases, which indicates that the mixed-flow pump stalls easily for smaller tip clearance. Under the deep stall condition, the influence of the leakage flow in the end wall area increases gradually with decrease in clearance. For small clearance, the leakage flow moves away from the suction surface to some distance to form a number of leakage vortex strips with the mainstream flow and flows over the leading edge of the next blade and then flows downstream into different flow passages, generating backflow and secondary flow separation at the blade inlet, which seriously damages the spatial structure of the inlet flow. This results in the earlier occurrence of stall. With increase in clearance, the leakage vortex develops along the radial direction towards the middle of the flow channel and large flow separation occurs in the downstream channel, which induces deep stall. For 0.8mm clearance, the whole impeller outlet passage is almost blocked by the backflow of the guide vane inlet, and a deep stall is induced.

Clearance control system

Abstract: Tip clearance control system having a plurality of impingement manifolds (40) to unevenly heat or cool a turbine shroud (28) such creating a non-uniform circumferential temperature distribution to produce ovalization of said turbine shroud (28) to conform to high load induced non-concentricities of the turbine rotor (52).