Tip Clearance Variation Research Articles

Investigation of varying tip clearance gap and operating conditions on the fulfilment of low-speed axial flow fan

Abstract The present study aims to identify the suitable tip clearance and volumetric flow rates for low-speed axial flow fans. The performance of an axial fan depends on various parameters like fan speed, available tip clearance gap, volumetric flow rate, power consumption, and working fluid. Leakage flow occurring at a rotating component such as a blade and solid casing of a ducted axial fan is typically linked to losses and the potential emergence of a rotating stall. The numerical analysis for this study uses the Reynolds Averaged Navier–Stokes equations with the k-omega SST turbulence model to perform the steady-state simulations by varying tip gap and volumetric flow rate. The results proved that the optimum performance was obtained with a tip clearance gap of 1 mm, and maximum fan efficiency was achieved at a volumetric flow rate of 3.9–4.5 m3/s. The novelty of this proposed work is to enhance the efficiency of axial flow fans with circular arc-cambered aerofoils using optimum tip clearance and volumetric flow rate through steady-state simulations. This method can be used in turbomachinery to improve fan performance.

The Influence of Blade Tip Clearance on the Flow Field Characteristics of the Gas–Liquid Multiphase Pump

Gas–liquid multiphase pumps are critical transportation devices in the petroleum and chemical engineering industries, and improving their conveyance efficiency is crucial. This study investigates the influence of blade tip clearance variations on the flow characteristics within a multiphase pump. Numerical simulations were conducted using Eulerian two-phase and SST k-ω turbulence models with four distinct tip clearance sizes (0 mm, 0.3 mm, 0.6 mm, and 0.9 mm). The performance curve, tip leakage flow (TLF), and internal gas distribution were subjected to analysis. The results indicate that the TLF is linearly related to the clearance size and traverses multiple flow passages, resulting in energy losses and a reduced pump head coefficient. Larger tip clearances (0.6 mm and 0.9 mm) exhibited a more uniform flow pattern, contrasting the irregularities seen with a 0.3 mm clearance. Compared to no tip clearance (0 mm), gas holdup within the impeller passages decreased by 18.39%, 39.62%, and 58.53% for clearances of 0.3 mm, 0.6 mm, and 0.9 mm, respectively, leading to decreased overall system efficiency. This study highlights the connection between tip clearance size and flow dynamics in multiphase pumps, offering insights for optimal tip clearance selection during multiphase pump design.

Effect of Tip Clearance on the Cavitation Performance of High-Speed Pump-Jet Propeller

To investigate the impact of tip clearance variation on the cavitation performance of a high-speed pump-jet propeller, Fluent software was employed for simulation calculations. The study utilized the RNG k-ε turbulence model and ZGB cavitation, conducting three-dimensional numerical simulations under both steady and transient conditions. A pump-jet propeller with a rated speed of 20,000 r/min was used to set three kinds of clearance for simulation, and the simulation proved to be reliable by comparison with the experiment. Initially, the analysis examined the effect of tip clearance on cavitation characteristics and cavitation volume under steady-state conditions, while also studying the distribution patterns of cavitation. Subsequently, the radial force and pressure pulsation of the jet propeller are analyzed by FFT processing, aiming at the influence of tip clearance on the structural strength of the pump-jet propeller. Under the design conditions, the smaller tip clearance shows better performance, while the larger tip clearance shows stronger anti-cavitation ability than the smaller clearance. In addition, the greater the tip clearance, the greater the radial force and pressure pulsation, which will adversely affect the pump-jet structure. The research results provide some references for further research on the effect of high-speed pump-jet propeller structures on performance.

A New Integrated Model for Simulating Adaptive Cycle Engine Performance Considering Variations in Tip Clearance

The low-fidelity simulation method cannot meet the requirements for predicting the performance of an adaptive cycle engine (ACE), especially when considering tip clearance variations in the compression and expansion systems. The tip clearances of the components of an ACE, such as the adaptive fan and turbine, vary drastically under different operating conditions. Though the tip clearance significantly impacts the engine’s performance, including its thrust and fuel consumption, variations in tip clearance are not considered in traditional ACE simulation models. This paper developed a new integrated model for predicting ACE performance, including multi-fidelity simulation models of the components and a newly developed, simplified model for predicting tip clearance. Specifically, the integrated model consists of a zero-dimensional (0D) engine performance simulation model, a three-dimensional (3D) adaptive fan numerical simulation model, a one-dimensional (1D) low-pressure-turbine (LPT) mean line model, and a multi-dimensional (MD) tip clearance prediction model. The integrated model solved the problem of considering the impact of tip clearance on an ACE and further improved the accuracy of thrust and fuel consumption predictions. Specifically, considering variations in the tip clearances under the design conditions, the differences in the thrust and specific fuel consumption (SFC) of the ACE are 1% and 0.3%, respectively. In conclusion, the integrated model provides a useful tool for evaluating the performance of an ACE while considering tip clearance variations.

Large eddy simulation of tip-leakage cavitating flow around twisted hydrofoil with effects of tip clearance and skew angle

Tip-leakage cavitating flow around hydrofoils has attracted much research interest, but the complex structures of tip separation vortex (TSV) and tip-leakage vortex (TLV) have not been clearly resolved and discussed with the effects of tip clearance and skew angle yet. In the present work, large eddy simulation (LES) with multi-level octree grid refinement is used to investigate the tip-leakage flows around a series of twisted hydrofoils with various skew angle and tip clearance. High resolution is guaranteed by the normalized grid sizes of y+<1, Δx+∼50 and Δz+∼10, through which the predicted flow meets the criterion that at least 80% of the turbulent kinetic energy is resolved. The TSVs are identified to grow from the entire lower edge of the tip and twine with the TLV into a primary vortex tube, which leads to counter-rotating induced vortices (IV) strongly twisted around the primary vortex in the case of medium tip clearance but weakened for small one. Cavitation effect significantly accelerates the roll-up process of the vortices so that the primary vortex is formed earlier. The tip-leakage flow turns from wake-like to jet-like when the clearance is reduced, but the jet velocity diminishes markedly for extremely small clearance. The hydrofoil skewness barely makes a lift on the vortex tube, distinctive from the effect of tip clearance variation. The adverse pressure gradient induced by the skew angle has significant effect on the laminar–turbulent​ transition of the flow. The tip vortex flow induces strongly characterized laminar ant turbulent flow regions on the suction side, which continuously changes with the variation of the skewness.

Effect of tip clearance variation in the transonic axial compressor of a miniature gas turbine at different Reynolds numbers

Degradation in the service or manufacturing tolerances can cause tip clearance variation, which adversely affects the stability and performance of compressors. In particular, for a miniature gas turbine, the size of the tip clearance ratio (the ratio of tip clearance to the tip chord length) is relatively large, thus it is more likely to operate at low Reynolds number. This study, therefore, numerically investigated the effect of tip clearance variation on the aerodynamic performance of a 1.5-stage transonic compressor at high and low Reynolds numbers using a 3D Reynolds averaged Navier-Stokes (RANS) solver that incorporates the SST k-ω turbulence model coupled with the γ-θ transition model. The results show that the aerodynamic performance and the tip flow field structure of the compressor change significantly with varying tip clearance.At high Reynolds number, the performance curves are essentially negatively linear with tip clearance, but the slopes sharply increase at medium tip clearance (0.9% C, C represents the tip chord length). At low Reynolds number, the varying trends of the sensitive curves for large tip clearances (0.9% C–1.8% C) are basically the same as that at high Reynolds number. However, for small tip clearances (0.3% C–0.9% C), the aerodynamic performance parameters fluctuate, namely, there is a peak aerodynamic performance at low Reynolds number. When considering the performance and surge margin of the compressor comprehensively, the best tip clearance is 0.6% C at high Reynolds number, but 0.9% C at low Reynolds number.

Aeroengine transient performance simulation integrated with generic heat soakage and tip clearance model

AbstractThe simulations and assessment of transient performance of gas turbine engines during the conceptual and preliminary design stage may be conducted ignoring heat soakage and tip clearance variations due to lack of detailed geometrical and structural information. As a result, problems with transient performance stability may not be revealed correctly, and corresponding design iterations would be necessary and costly when those problems are revealed at a detailed design stage. To make an engine design more cost and time effective, it has become important to require better transient performance simulations during the conceptual and preliminary design stage considering all key impact factors such as fuel control schedule, rotor dynamics, inter-component volume effect as well as heat soakage and tip clearance variation effects. In this research, a novel transient performance simulation approach with generically simplified heat soakage and tip clearance models for major gas path components of gas turbine engines including compressors, turbines and combustors has been developed to support more realistic transient performance simulations of gas turbine engines at conceptual and preliminary design stages. Such heat soakage and tip clearance models only require thermodynamic design parameters as input, which is normally available during such design stages. The models have been implemented into in-house transient performance simulation software and applied to a model twin-spool turbojet engine to test their effectiveness. Comparisons between transient performance simulated with and without the heat soakage and tip clearance effects demonstrate that the results are promising. Although the introduced heat soakage and tip clearance models may not be as accurate as that using detailed component geometrical information, it is able to include the major heat soakage and tip clearance effects and make the transient performance simulations and analysis more realistic during conceptual and preliminary engine design stage.

An Improved Blade Vibration Parameter Identification Method considering Tip Clearance Variation

Blade tip timing (BTT) technology is the most effective means for real-time monitoring of blade vibration. Accurately extracting the time of blade tip reaching the sensors is the key to ensure the accuracy of the BTT system. The tip clearance changes due to various complex forces during high-speed rotation. The traditional BTT signal extraction method does not consider the influence of tip clearance change on timing accuracy and introduces large timing errors. To solve this problem, a quadratic curve fitting timing method was proposed. In addition, based on the measurement principle of the eddy current sensors, the relationship among the output voltage of the eddy current sensor, tip clearance, and the blade cutting magnetic line angle was calibrated. A multisensor vibration parameter identification algorithm based on arbitrary angular distribution was introduced. Finally, the experiments were conducted to prove the effectiveness of the proposed method. The results show that in the range of 0.4 to 1.05 mm tip clearance change, the maximum absolute error of the timing values calculated by the proposed method is 26.0359 us, which is much lower than the calculated error of 203.7459 us when using the traditional timing method. When the tip clearance changed, the constant speed synchronous vibration parameters of No. 0 blade were identified. The average value of the vibration amplitude is 1.0881 mm. Compared with the identification results without changing tip clearance, the average value error of the vibration amplitude is 0.0017 mm. It is proved that within the blade tip clearance variation of 0.4 to 0.9 mm, the timing values obtained by the proposed timing method can accurately identify the vibration parameters of the blade.

High-Precision Extraction Method for Blade Tip-Timing Signal with Eddy Current Sensor

Online monitoring of high-speed rotating blades has always been a hot topic. Of the various methods, the blade tip timing (BTT) technique, based on eddy current sensors, is considered to be the most promising. However, BTT signals are easily influenced by various factors, which means that the accurate extraction of BTT signals remains a challenge. To try to solve this problem, the causes of measurement error were analyzed. The three main reasons for the error were established: the variation in blade tip clearance, the interference of background noise, and the asymmetry of the blade tip shape. Further, pertinent improvement methods were proposed, and a compensation method was proposed for the errors caused by the variation of tip clearance. A new denoising and shaping algorithm based on ensemble empirical mode decomposition (EEMD) was introduced for the errors caused by background noise. Additionally, an optimal installation position of the sensor was also proposed for the errors caused by the asymmetry of the blade tip shape. Finally, simulations and experiments were used to demonstrate the improved methodology. The results show that the measurement error on vibration amplitude and vibration frequency using the proposed method is less than 2.89% and 0.17%, respectively, which is much lower than the traditional method (24.44% and 0.39%, respectively).

Investigation on tip clearance control for the high-pressure rotor of an uncooled vaneless counter-rotating turbine

In order to develop a tip clearance control system for an uncooled vaneless counter-rotating turbine, tip clearance variation of its high pressure rotor blade at off-design conditions is analyzed. Aero-thermal interaction simulation is performed to predict the temperature and deformation of the solid blade. At operating conditions with rotating speeds greater than 60% design value and expansion ratios greater than 85% design value, the blade tip clearance height at leading edge remains unchanged when the expansion ratio decreases, meanwhile that at trailing edge decreased obviously. However, the tip clearance height variations at the leading edge and trailing edge are almost the same in a conventional subsonic turbine at such conditions. The cause is that the flow in the high-pressure rotor is choked at these conditions. The choked flow results in that the fluid and solid blade temperatures upstream of the throat are not affected by the back pressure and only those downstream of the throat increases with the back pressure. Consequently, the blade height at leading edge keeps constant, and that at trailing edge varies because of thermal expansion. To avoid the rubbing of the blade and case, the blade height at trailing edge is diminished by 30%. As a result, the blade tip clearance height at low speed operating conditions increases in axial direction. Such a design leads to a stronger tip leakage flow. More flow losses might be generated. Therefore, a casing cooling method is proposed to control the blade tip clearance height at leading edge and trailing edge respectively. The deformations of the casing with different mass flow rate of cooling air at design and off-design conditions are calculated. It shows that the blade tip clearance heights at leading edge and at trailing edge of the rotor can be well controlled with appropriate amount of cooling air.

Axial Turbine Performance Estimation During Dynamic Operations

During service, a turbine engine undergoes frequently dynamic operations. Because of the changes in mass flow, temperature, pressure, as well as the different reaction of the components of turbine to these changes, the turbine performances may vary significantly. It is critical to understand and quantify these variations to design and integrate the turbine to the engine. This paper presents a study of the performances and the variation of the performances for an axial gas turbine across its operating envelope. Numerical simulations are used to describe the flow across the turbine and to estimate the turbine maps. Using theoretical charts for typical turbine thermal expansion, the variation of tip clearance across the working line is approximated. Because of the changes of the tip clearance, using a single geometry may not supply relevant information during real dynamic operations. In order to eliminate these additional errors in the numerical study, a number of turbines maps are recalculated for different tip clearances, respectively to engine regimes. With the resulting data, the working line is recalculated across multiple maps. The comparison between the two working lines is presented as well as the study of performance variation of the turbine across the operation envelope and the influence of tip clearance at different regimes.

Optimizing bidirectional impulse turbines for thermoacoustic engines.

The design of a bidirectional impulse turbine to convert thermoacoustic power into electricity is experimentally optimized. The turbine efficiency is measured for rotors with and without a shroud ring and for a varying tip clearance. Furthermore, the axial spacing between the guide vanes and rotor is varied with respect to the displacement amplitude of the acoustic wave. All measurements are carried out for several turbine loads and acoustic frequencies. For a chosen implementation, a design study on the guide vane and rotor blade geometry is presented to further optimize the bidirectional impulse turbine for thermoacoustic engines.

Massively Parallel Large Eddy Simulation of Rotating Turbomachinery for Variable Speed Gas Turbine Engine Operation

Gas turbine engines are required to operate at both design and off-design conditions that can lead to strongly unsteady flow-fields and aerodynamic losses severely impacting performance. Addressing this problem requires effective use of computational fluid dynamics tools and emerging models that resolve the large scale fields in detail while accurately modeling the under-resolved scale dynamics. The objective of the current study is to conduct massively parallel large eddy simulations (LES) of rotating turbomachinery that handle the near-wall dynamics using accurate wall models at relevant operating conditions. The finite volume compressible CharLES solver was employed to conduct the simulations over moving grids generated through Voronoi-based unstructured cells. A grid sensitivity analysis was carried out first to establish reliable parameters and assess the quality of the results. LES simulations were then conducted to understand the impact of blade tip clearance and operating conditions on the stage performance. Variations in tip clearance of 3% and 16% chord were considered in the analysis. Other design points included operation at 100% rotor speed and off-design conditions at 75% and 50% of the rotor speed. The simulation results showed that the adiabatic efficiency improves dramatically with reduction in tip gap due to the decrease in tip leakage flow and the resulting flow structures. The analysis also showed that the internal flow becomes highly unsteady, undergoing massive separation, as the rotor speed deviates from the design point. This study demonstrates the capability of the framework to simulate highly turbulent unsteady flows in a rotating turbomachinery environment. The results provide much needed insight and massive data to investigate novel design concepts for the US Army Future Vertical Lift program.

Turbine blade tip clearance determination using microwave measurement and k-nearest neighbour classifier

Turbine blade tip clearance and deformation can be monitored by measurement of scattering parameters. In this research, a k-band microwave sensor has been simulated, optimized and implemented in computer simulation technology software which can detect tip clearance variations by measurement of the scattering parameters using a network analyzer. The open-ended circular waveguide with the tip of the turbine blades forms a cavity resonator known as a microwave sensor. Scattering parameters can be used as fingerprints of the blade that are altered due to changes in tip clearance and deformation in accordance with the theory of small perturbations in cavity resonators. In this research, a new method for interpretation of the measured scattering parameters is presented that is based on measuring indices and the k-nearest neighbor classifier. It has been shown that the k-NN classifier provides acceptable accuracy for detection and determination of the blade tip clearance and deformation.

Effect of tip clearance size on the performance of a low-reaction transonic axial compressor rotor

This study aimed to enhance the understanding of flow phenomena in low-reaction aspirated compressors. Three-dimensional, multi-passage steady and unsteady numerical simulations are performed to investigate the performance sensitivity to tip clearance variation on the first-stage rotor of a multistage low-reaction aspirated compressor. Three kinds of tip clearance sizes including 1.0τ, 2.0τ and 3.0τ are modeled, in which 1.0τ corresponds to the designed tip clearance size of 0.2 mm. The steady numerical simulations show that the overall performance of the rotor moves toward lower mass flow rate when the tip clearance size is increased. Moreover, energy losses, efficiency reduction and stall margin decrease are also observed with increasing tip clearance size. This can be mostly attributed to the damaging impact of intense tip clearance flow. For unsteady simulation, the result shows periodical oscillation of the tip leakage vortex and a “two-passage periodic structure” in the tip region at the near-stall point. The occurrence of the periodical oscillation is due to the severe interaction between the tip clearance flow and the shock wave. However, the rotor operating state is still stable at this working point because a dynamic balance is established between the tip clearance flow and incoming flow.

Numerical Analysis of the Acoustic Field of a Ducted Axial Fan at Varying Tip Clearances

Numerical Analysis of the Acoustic Field of a Ducted Axial Fan at Varying Tip Clearances

Numerical investigation of tip flow dynamics and main flow characteristics with varying tip clearance widths for an axial-flow pump

The effects of varying tip clearance widths on tip flows dynamics and main flows characteristics for an axial-flow pump are studied employing computational fluid dynamics method. An analysis is presented for the distributions of turbulent kinetic energy, mean axial velocity, and mean vorticity magnitude at the specific flow rate of 0.7 Q BEP , focusing on flow patterns in the tip region with different tip clearance widths and associated flows. From the simulation results we find that the flow structure of tip vortex and its transportation strongly depend on the tip clearance width, especially for the extension of tip leakage vortex, appearance of induced vortex and the area of tip separation vortex. For a small clearance of 0.15 mm at 0.7 Q BEP, there is no tip separation vortex at the tip. When tip clearance width becomes larger, a tip separation vortex attaches more on the surface of blade tip as well as vortex intensity of tip flows increases. For tip clearances of 0.9 and 1.2 mm, there is a small part of induced vortex near the blade leading edge. Meanwhile, no induced vortex can be captured for tip clearances of 0.15 and 0.45 mm. The relative angle between the blade chord and tip leakage vortex trajectory reduces gradually when tip clearance width increases from 0.45 to 1.2 mm. Additionally, the radial position of tip leakage vortex core moves inwards as tip clearance width increases. Furthermore, a larger tip clearance width has greater effects on the main-stream characteristics especially near the shroud, which is due to more energy being exchanged between tip flows and main flows. At the flow rate 0.7 Q BEP, both the efficiency and head of the pump reduce with an increasing tip clearance because of greater energy loss.

涡轮叶片三维叶尖间隙光纤检测系统

涡轮叶片三维叶尖间隙光纤检测系统

Analysis Effect of Duct Length– Nozzle Diameter Ratio and Tip Clearance Variation on the Performance of K-Series Propeller

One type of ship propeller is a ducted propeller. Ducted propellers are propellers with sheath or duct that can increase thrust on the propeller and useful for directing the flow of water that will pass through the Propeller. In addition to improving thrust, ducted propellers can also increase torque compared with no duct. The basic theory of momentum for this ducted propeller operation has been used by Horn (1940). In order for the efficiency of the thrust to be of good value, the volume of water passing through the propeller should be as large as possible, with the smallest possible flow velocity. The most important components of ducted propeller are Ld / D and tip clearance. Ld / D is a coefficient comparison between the length of the casing / duct and the diameter of the duct, while the tip clearance is the distance between the tip of the propeller with an inner diameter of the duct. Both components are discussed in this study. The purpose of this research is to know the performance of propeller after given variation on Ld / D and tip clearance. The method used for propeller analysis is Computational Fluid Dynamic (CFD). Based on simulation result, the most optimal propeller performance is ducted propeller with Ld / D = 0.5 and tip clearance 40 mm

Investigation of Performance and Rotor Tip Flow Field in a Low Speed Research Compressor with Circumferential Groove Casing Treatment at Varying Tip Clearance

Experimental investigations in a single-stage low speed axial research compressor are presented. The influence of four different rotor tip clearances on the overall compressor performance and on the rotor tip flow field is investigated in configurations with and without circumferential groove casing treatments. Piezo-resistive pressure transducers are used to capture the unsteady flow field in the rotor tip region. The investigated casing groove is effectively working at the three largest investigated tip clearance sizes. The largest achieved operating range increase by the groove is 6.9%. The groove can delay the upstream movement of the flow interface between leakage flow and main flow and thus increase the stable operating range. Rotating instabilities are shown to exist at large tip clearance sizes in throttled operating conditions. Their amplitudes can be damped by the casing groove. No modal activities could be detected in the current single-stage compressor build.