Tip clearance

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

Turbine Tip Clearance Flow Control using Plasma Actuators

Abstract: The tip clearance gap leakage ∞ow is of continuing concern in reducing e‐ciency losses that occur within turbines. Active ∞ow control using a blade-tip-mounted unsteady plasma actuator was implemented in a low pressure linear turbine cascade. Downstream ∞ow velocity and pressure were acquired using a flve-hole probe to document changes in leakage vortex size and strength. Reynolds numbers of 5£10 4 and 10 5 for tip gaps of 4% and 1.56% of axial chord were examined for unactuated and actuated cases. Due to the large ∞ow angles seen in the leakage vortex at a 4% gap size, the probe was unable to acquire the downstream pressure because the calibration region of the probe was exceeded. The extensive three-dimensionality of the ∞owfleld in the tip region has proven di‐cult to measure for low velocities. However, for the smaller 1.56% gap, the leakage vortex size is reduced over the 4% gap, which allows for measurement of actuator efiectiveness on the downstream ∞owfleld. Here, actuation achieved a 29.5% reduction in maximum pressure loss at an axial chord Reynolds number of 10 5 , while at a Reynolds number equal to 5 £ 10 4 , there was a 14.7% reduction. These results are dependent on the unsteady frequency the actuator, although these results show a signiflcant beneflcial change in the tip gap ∞ow.

Tubomachinery blade vibration amplitude measurement through tip timing with capacitance tip clearance probes

Abstract: Turbomachinery blade vibrations can cause high cycle fatigue (HCF), which reduces blade life. In order to observe this vibration a non-intrusive monitoring system is sought. The vibration can be detected by measuring blade tip timing since in the presence of vibration the blade timing will differ slightly from the passing time calculated from rotor speed. Much research and development has gone into investigating the ability of optical probes to achieve this. However, this paper looks at the potential for a dual use capacitance probe sensor to measure both tip timing and tip clearance. This paper provides new insights into the ability of a commercially available capacitance probe tip clearance measurement system for application as a non-intrusive turbomachinery blade tip timing measurement device. This is done by correlating capacitance probe tip timing results with simultaneously measured blade-mounted strain gauge vibration results and precise rotational speeds. Blade tip vibration amplitudes are measured using capacitance probes and compared to strain derived vibration levels. Thus the characterisation and quantification of the performance of the capacitance probe system when measuring blade vibration on a full-sized low-speed research compressor is analysed and reported.

Tip clearance effects in a turbine rotor : Part I : Pressure field and loss

Abstract: This paper presents an experimental investigation of the effects of the tip clearance flow in an axial turbine rotor. The effects investigated include the distribution and the development of the pressure, the loss, the velocity, and the turbulence fields. These flow fields were measured using the techniques of static pressure taps, rapid response pressure probes, rotating five-hole probes, and Laser Doppler Velocimeter. Part I of this paper covers the loss development through the passage, and the pressure distribution within the passage, on the blade surfaces, on the blade tip, and on the casing wall. Regions with both the lowest pressure and the highest loss indicate the inception and the trace of the tip leakage vortex. The suction effect of the vortex slightly increases the blade loading near the tip clearance region. The relative motion between the turbine blades and the casing wall results in a complicated pressure field in the tip region. The fluid near the casing wall experiences a considerable pressure difference across the tip. The highest total pressure drop and the highest total pressure loss were both observed in the region of the tip leakage vortex, where the loss is nearly twice as high as that near the passage vortex region. However, the passage vortex produces more losses than the tip leakage vortex in total. The development of the loss in turbine rotor is similar to that observed in cascades. Part II of this paper covers the velocity and the turbulence fields.Copyright © 2000 by ASME

Turbine Engine Clearance Control Systems: Current Practices and Future Directions

Abstract: Improved blade tip sealing in the high pressure compressor (HPC) and high pressure turbine (HPT) can provide dramatic reductions in specific fuel consumption (SFC), time-on-wing, compressor stall margin, and engine efficiency as well as increased payload and mission range capabilities. Maintenance costs to overhaul large commercial gas turbine engines can easily exceed $1M. Engine removal from service is primarily due to spent exhaust gas temperature (EGT) margin caused mainly by the deterioration of HPT components. Increased blade tip clearance is a major factor in hot section component degradation. As engine designs continue to push the performance envelope with fewer parts and the market drives manufacturers to increase service life, the need for advanced sealing continues to grow. A review of aero gas turbine engine HPT performance degradation and the mechanisms that promote these losses are discussed. Benefits to the HPT due to improved clearance management are identified. Past and present sealing technologies are presented along with specifications for next generation engine clearance control systems.