Influence Of Tip Clearance Research Articles

Tip clearance influence on the performance of high-speed micro-pumps

The fast-paced development of the aerospace and shipping industry is promoting the development of lightweight and high-speed transfer pumps. High-speed micro-pumps with semi-open impellers are highly sensitive to tip clearance (TC), which crucially influences the head and efficiency. This study proposes a new design for a high-speed micro-semi-open impeller centrifugal pump with a 19 000 rpm rotational speed and 30 m hydraulic head. The performance of the proposed centrifugal pump under different inlet corrosion allowances and different impeller TC ratios (0.05, 0.08, 0.11, and 0.14) is investigated through numerical simulations and experiments. The interaction process between the leakage and main flows in the tip gap is recorded with a high-speed camera and is numerically calculated. The stability of the internal flow field is optimal under smaller TCs. This study provides the optimal TC and guidance for designing high-speed micro-pumps.

Study on the Influence of Tip Clearance on Cavitation Performance and Entropy Production of an Axial Flow Pump

The clearance existing between the impeller rim and the adjacent shroud within the pump configuration establishes conducive circumstances for the initiation of cavitation. The bubbles generated by cavitation will flow forward with the water, blocking the channel, and result in the degradation of the pump performance. When the cavitation is severe, vibration and noise will be generated. The impact formed by the collapse of the bubbles will seriously erode the blades and form pits on the blade surfaces. Drawing upon the outcomes derived from numerical simulations, this paper investigates the relationship between tip clearance and cavitation in an axial flow pump, with a specific focus on energy dissipation characteristics. The principal findings indicate that the dimensions of the tip clearance predominantly influence the spatial distribution of the tip leakage vortex (TLV) cavitation. The entropy production rate distribution at the tip correlates with both the cavitation level of the pump and the extent of the tip clearance. The shedding phenomenon of the TLV becomes more evident when analyzing the distribution of entropy production rates. During cavitation, an increased tip clearance is associated with a reduction in the dissipation of viscous entropy production within the impeller domain, and the entropy production resulting from turbulent dissipation significantly surpasses that arising from viscous dissipation.

Influence of tip clearance on internal energy loss characteristics of axial flow pumps under different operating conditions

Axial flow pumps possess a unique structure where there must be clearances between the impeller and the piping wall, usually not exceeding 0.1% of the impeller diameter. Despite the small size of the clearance, the internal micro-vortex structures have a non-negligible impact on the main flow field of the impeller. Under the action of the pressure difference between the suction and pressure surfaces of blades, some fluids form high-energy jets in the tip clearance area, known as tip leakage vortices (TLVs). TLV interacts with the flow of the main flow field, exerting a significant impact on the internal flow state, energy loss, and hydraulic performance of the pump. To identify the influence of TLVs on the internal flow field and energy loss of axial flow pumps, this work uses a modified partially averaged Navier–Stokes (PANS) model to perform full flow field numerical calculations for a certain axial flow pump and conducts a comparative analysis of the internal flow field energy dissipation, unsteady vortex structures, energy loss, and other characteristics under three different tip clearances: 0.2 mm (0.05%D), 0.6 mm (0.15%D), and 1.0 mm (0.25%D) based on the energy transport theory. The results indicate that at optimal operating conditions, the internal energy distribution of the fluid in each flow passage is uniform, and the energy loss is primarily caused by axial backflow in the tip area; under critical rotating stall conditions, clearance size affects the distribution state of enstrophy in the guide vane flow passage, leading to average enstrophy being highest at the rim area and the most uneven distribution of enstrophy, inducing larger energy loss in the impeller; during deep stall conditions, the unevenness of internal energy distribution is stronger than that under critical stall conditions, but the overall energy loss within the impeller flow area is lower than that under critical stall conditions, while energy unevenness is mitigated as the tip clearance size increases.

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.

Tip clearance influence on hydrodynamic performance and pressure fluctuation of a composite ducted propeller using a two-way FSI method

With the development of advanced materials, composite materials have been studied by researchers over the world to make them more applicable to many applications, especially in the marine industry. As an important component of marine vehicles, propellers have been studied over decades to achieve the goals of increasing hydrodynamic performances and structural properties. However, traditional marine propellers manufactured with metallic materials have many limits. Therefore, the use of composite material to improve the performances of the propeller has become a research hotspot since their great structural performances and material damping properties can improve the comprehensive performance of the propellers such as increased hydrodynamic performances and reduced pressure fluctuation characteristics. The ducted propeller is a typical marine propulsor, which has a tip clearance between the blade tip and the inner face of the duct that can cause a complex fluid flow around the blades and influence the performance of the propeller. In this research, the tip clearance influence on hydrodynamic performance and pressure fluctuation of a composite ducted propeller compared with a metallic equivalent is calculated using a two-way fluid-structure interaction (FSI) method. The results indicate that the use of composite materials with a proper stacking sequence on the ducted propeller blade with a smaller tip clearance size corresponding to GSR = 0.417 can achieve good hydrodynamic properties for the propeller, and it has a significant inhibiting effect on pressure fluctuations on the blade surface.

The Influence of Tip Clearance on the Performance of a High-Speed Inducer Centrifugal Pump under Different Flow Rates Conditions

The influence mechanism of the blade tip clearance (TC) of an inducer on the performance of a centrifugal pump at high speed was researched under different flow rate conditions in this work. An experiment on the pump’s external performance was carried out, and numerical calculation was also performed under four different TCs. The full characteristic performance curves, static pressure and pressure pulsation distributions of the pump were obtained. Through the research and analysis, it was found that the influence of the TC on the efficiency and the head of the centrifugal pump are related to the flow rate. Under the influence of a large flow rate, the increase in the TC is helpful to improve the efficiency and the head of the pump. The increase in the TC helps to weaken the gap jet effect on the inducer. The inlet jet of the inducer, caused by TC leakage, will form a low-pressure vortex zone at the inlet of the inducer. The splitter-bladed inducer’s pressure pulsation is affected by the TC. The peak pressure pulsation at the monitoring point at the short blades is larger than that at the long blades. With the increase in TC, the cavitation degree at the inlet of the long blade of the inducer is decreased, while the cavitation degree at the short blade is deepened. It is also found that the TC has little effect on the radial force of the inducer and the impeller. These results will provide the design basis for the tip clearance of an inducer.

Influence of Tip Clearance on Cavitation Characteristics of an Inducer of Turbopump: CFD Study

The tip clearance, a compact gap between the inducer blade tip and casing wall, is critical to both the liquid leakage and cavitation-induced forces of a turbopump. In this study, we numerically investigate the effect of tip clearance on the cavitation characteristics of an inducer. Six different tip clearances, 0.1, 0.3, 0.5, 1.0, 1.5, and 2 mm, namely Models A–F, were designed to evaluate the cavitation performance, cavity structure, blade loading, radial force, etc. Model D (1.0 mm) had the relatively highest head coefficient and smallest cavity area on each blade as compared to all other models. The pressure coefficient distribution and blade loading further confirmed that Model D can maintain a higher pressure head and better suppress the cavitation onset than the other models. The radial force signals in the time and frequency domains show that Model D has an intermediate force magnitude with slightly higher noises at the rotating frequency and its harmonic frequencies. Model D also has a relatively smaller vortex region and smaller vortex strength (λ2 criterion). In short, all results show that Model D is the best alternative to balance the complex interactions of the bulk flow and tip leakage flow, compromising the hydraulic head and rotating cavitation.

Analysis and modeling of the tip leakage flow on the performance of small-scale turbopumps for ORC applications

• An automated design model is developed to generate impeller geometries suitable for organic Rankine cycles. • The influence of tip clearance is investigated and modeled. • At high blade outlet angles, the effects of tip clearance and flow rate on the slip factor diminish. • The head rise decreases with the tip clearance ratio. • Feedforward neural networks are trained to model the slip factor and head loss coefficient of unshrouded centrifugal pumps. In this paper, the influence of tip clearance on the performance of small-scale turbopumps is studied numerically on extensive parameter ranges suitable for organic Rankine cycle applications. A novel and fully parameterized design model is developed and used to generate a wide range of turbopumps and their fluid domains to carry out three-dimensional computations across the impeller stage. Impellers are investigated at different operating conditions, and the accomplished results are analyzed to characterize the performance at design and off-design conditions. The CFD calculations demonstrate that the slip factor is dependent not only on its geometrical parameters, as considered by most correlations, but also on its operating conditions. The slip factor decreased almost linearly as the flow rate increased. In addition, the tip clearance ratio influences the slip factor, and its influence is non-linear. The head rise decreases as the tip clearance ratios increase. However, for radial impellers, a higher head rise was observed for small tip clearance ratios (<0.10). The numerical data is employed to infer reduced-order models for considering the tip clearance effect in the early-phase design process of small-scale turbopumps. The models predict the CFD data with an average relative deviation of 3.6 % and 5.8 % for the slip factor and the head loss coefficient, respectively.

Effect of Tip Clearance on the Cavitation Flow in a Shunt Blade Inducer

In order to study the effect of tip clearance on the internal cavitation stability of a shunt blade inducer, an external characteristics experiment of a centrifugal pump with a shunt blade inducer was carried out. Based on the turbulence model and mixture model, the cavitating flow in a centrifugal pump with the inducer was numerically simulated. The influence of tip clearance on the cavitating flow in a shunt inducer was studied and analyzed. Through the research, it was found that tip clearance has a certain influence on the critical cavitation coefficient. The existence of the tip clearance caused a significant leakage vortex near the inducer’s inlet and a strong transient effect was shown. The location and degree of cavitation caused by the tip leakage are clarified in this paper. Tip clearance has a great impact on the pressure distribution on a shunt blade inducer. The influence law of tip clearance on an inducer’s blade load distribution was clarified. The results showed that tip clearance has a significant effect on the cavitation of a shunt blade inducer under low flow rate conditions.

Influences of tip clearance on flow and heat transfer characterstics of open type micro pin fin heat sink

Microchannel heat sink without any tip clearance i.e. completely closed microchannels have been focused and widely studied. In the present work, detailed comparative analysis has been performed between open and closed micro pin fin configurations of the heat sink. Keeping the constant channel height of 2.0 mm, three different micro pin fin heat sinks with tip clearance of 0%, 25% and 50% of channel height were fabricated and analyzed. Square cross-section fins are considered and arranged in inline fashion. An additional plain channel (without any pin fin) is also examined for the sake of comparison and completeness of the study. The experiments have been conducted using deionized water as the working fluid and copper as microchannel substrate. Present work aims to recognize the importance of tip clearance and quantify its suitable value that facilitates better heat transfer rate. Numerical predictions further elaborate the physical insight of the coolant flow behavior evolved due to the presence of tip clearance in the heat sink. Findings of the present study indicate that tip clearance of 50% results in lesser heat transfer coefficients due to considerably lower net convective surface area. Whereas, tip clearance of 25% has shown superior thermal performance amongst all the configurations explicitly at Reynolds number more than 350. In addition to the net convective surface area, major factors that promote enhanced heat transfer are dispersed fluid flow behavior in the confined space of tip clearance which propagates thinner boundary layer, three dimensionalities in flow and augmented fluid mixing. Moreover, heat sink with tip clearance has also shown lesser pressure drop compared to closed microchannel due to reduced flow obstructions. It has been concluded that tip clearance may have positive impact on overall thermal performance but up to the certain limit.

The Effect of Clearance on Energy Dissipation for the Roots Power Machine Based on Low-Quality Energy Recovery

As a new type of waste heat conversion machine, the roots power machine can convert low-quality waste heat resources that are difficult to use into mechanical energy. In order to study the influence of tip clearance and radial clearance on the roots power machine, experimental studies were conducted with the roots power machine having different combination of tip and radial clearances and their influence on the performance of the roots power machine was examined. A parametric study was undertaken using CFD to find the sensitivity of these clearances in influencing the performance of roots power machine in the range of 0.2-0.5 mm. From the analysis, it was inferred that radial clearance was sensitive for clearance range of 0.25-0.5 mm and tip clearance in the range of 0.2-0.25 mm. Reduction in clearance from 0.5 mm to 0.2 mm caused an increase of 10.368 and 11.423 % in mechanical and volumetric efficiency respectively.

Analysis of Tip Clearance Effect on the Transportation Characteristics of a Multiphase Rotodynamic Pump Based on the Non-Uniform Bubble Model

The multiphase rotodynamic pump is widely used in petroleum and gas exploitation, and blade tip clearance may cause flow instability and performance deterioration. In the present work, the influence of tip clearance on the transportation characteristic in a multiphase rotodynamic pump is investigated based on the non-uniform bubble model, in which the bubbles’ coalescence and break-up are considered. The influence mechanism of tip clearance on the energy performance is revealed. The results show that the leakage flow rate increases linearly with the increase in tip clearance, but variation in pump energy performance shows the opposite trend. In addition, a larger tip clearance results in a sharply decreased pressure increment in the impeller, while in the guide vane, the increment is raised slightly. For the 0 mm tip clearance condition, a positive vortex (relative to the impeller rotation direction) is observed in the impeller passage. However, the opposite leakage vortex is also found in the region near the tip clearance when the tip clearance is considered, and the vortex strength increases for a larger tip clearance.

Influence of Tip Clearance on the Hydrodynamic Damping Characteristics of a Hydrofoil

AbstractTip clearance in hydraulic machines may complicate the fluid–structure interaction (FSI) effects. In this investigation, a mode-based approach (modal work) is evaluated and employed to quantitatively predict the added mass, added stiffness, and hydrodynamic damping ratio, in relation to the first-order bending mode of a vibrating hydrofoil. The investigated relative tip clearance ranges from 0.067% to 2% of the span length. The predicted vortex shedding frequency, natural frequency, and hydrodynamic damping ratio of the hydrofoil are in good agreement with the previously published experimental results, with relative deviations within 9.92%, 6.97%, and 11.23%, respectively. Simulation results show that the added mass, added stiffness, and hydrodynamic damping ratio increase inversely as the tip clearance increases. In particular, as the relative tip clearance increases from 0.067% to 2%, the added mass in still water, the added stiffness, and hydrodynamic damping ratio at a velocity of 10 m/s decrease by 18.66%, 9.36%, and 27.99%, respectively. As the tip clearance increases, the inversely increased pressure difference between the upper and lower surfaces of the vibrating hydrofoil is the main reason for the inversely increased hydrodynamic damping ratio. This is due to the energy leakages via the tip clearance region increase as the tip clearance increases, which may cause less fluid force to resist the vibration of the hydrofoil, resulting in less negative modal work done by the fluid load on the hydrofoil.

Influence of Tip Clearance on Centrifugal Compressor IGV Regulation and Improvement

In order to avoid collision with the end wall of the casing when the guide vane rotates around its own rotating axis in a centrifugal compressor, a circular gap will be left at the top of guide vane. Part of the gas flow through the clearance cannot be effectively regulated, and the tip clearance leakage vortex is formed, which has an impact on the mainstream and makes the compressor performance decline. In order to solve this problem, in this paper, three improved schemes of guide vane channel structure, including rectangular channel, cambered channel, and globular channel, were put forward, which can effectively improve the regulation ability of guide vane. Comparing these three improved channels with the original one, the stable operating range of the compressor was enlarged; the power consumption of the compressor was reduced and the efficiency of the compressor was improved. By comprehensive comparison, the cambered channel has better performance and is easier to process, which has potential to be widely used in practice.

Influence of Tip Clearance on Flow Characteristics of Axial Compressor

This paper studies the influence of tip clearance on the flow characteristics related to the performance. Based on full-passage numerical simulation with experimental validation, several clearance models are established and the performance curves are obtained. It is found that there exists an optimum clearance for the stable working range. By analyzing the flow field in tip region, the role of the tip leakage flow is illustrated. In the zero-clearance model, the separation and blockage along the suction side is the main reason for rotating stall. As the tip clearance is increased to the optimum value, the separation is suppressed by the tip leakage flow. However, with the continuing increasing of the tip clearance, the scale and strength of the tip clearance vortex is increased correspondingly. When the tip clearance is larger than the optimum value, the tip clearance vortex gradually dominates the flow field in the tip region, which can increase the unsteadiness in the tip region and trigger forward spillage in stall onset.

Influence of tip clearance and cavity depth on heat transfer in a cutback squealer tip

Numerical simulations are conducted to present the aerothermal performance of a turbine blade tip with cutback squealer rim. Two different tip clearance heights (0.5%, 1.0% of the blade span) and three different cavity depths (2.0%, 3.0%, and 6.0% of the blade span) are investigated. The results show that a high heat transfer coefficient (HTC) strip on the cavity floor appears near the suction side. It extends with the increase of tip clearance height and moves towards the suction side with the increase of cavity depth. The cutback region near the trailing edge has a high HTC value due to the flush of over-tip leakage flow. High HTC region shrinks to the trailing edge with the increase of cavity depth since there is more accumulated flow in the cavity for larger cavity depth. For small tip clearance cases, high HTC distribution appears on the pressure side rim. However, high HTC distribution is observed on suction side rim for large tip clearance height. This is mainly caused by the flow separation and reattachment on the squealer rims.

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.

Influence of Tip Clearance on Unsteady Flow in Automobile Engine Pump

Influence of Tip Clearance on Unsteady Flow in Automobile Engine Pump

The influence of tip clearance and shape of pin fins on the heat transfer performance and friction factor in aluminum silicon alloy heat exchanger

In this article, the coupled heat transfer model was applied to investigate the effect of the tip clearance and shape of pin fins on the heat transfer performance and friction factor in the high temperature region of aluminum silicon alloy heat exchanger. The tip clearance ranged from 1 mm to 8 mm, and the shape of pin fins was the circular, drop-A and drop-B. The results showed that as the tip clearance increases, the outlet flue gas temperature increases, while the Nusselt number, the pressure loss and the friction factor decreases. For the circular pin fin, the difference of outlet flue gas temperature between it and drop-A was very slight, but both were higher than drop-B. In addition, circular pin fin had the minimum values of pressure loss friction factor. Comprehensively considering the heat transfer performance and friction factor, the thermo-hydraulic performance of circular pin fin with the tip clearance of 4 mm was superior to other cases.

Numerical investigation of tip leakage vortex cavitation

Tip leakage vortex cavitation is a concern for axial hydraulic turbines. Generally, cavitation may occur in the core of the TLV, often leading to erosion of the runner blades and the casing. The objective of this paper is to study the effects of this phenomenon on the hydrodynamics characteristics of a standard NACA0009 blade. Numerical simulations of the present study are carried out using the ANSYS CFX. The k–ω SST turbulence model and the Schnerr-Sauer cavitation model are respectively used for the modeling of turbulence and cavitation. In the first step of this study, the effect of considering cavitation phenomenon and transient state is investigated by monitoring the coordinate of the vortex core center and comparing them with the experimental data. The steady state simulation with cavitation modeling leads to acceptable prediction of vortex core center position and the unsteady cavitation modeling further improved the accuracy of the predictions. The influence of tip clearance, incidence angle and cavitation number on the hydrodynamics characteristics of the hydrofoil is further studied. The results demonstrate that incidence angle and cavitation number have more pronounced effects on improving the lift to drag ratio in comparison to the tip clearance. According to performance curves, the maximum lift coefficient is obtained by incidence angle of 12 degree in the cavitation number range of 1<σ<1.25.