Showing papers on "Tip clearance published in 2017"
TL;DR: In this paper, the authors show that the development of a leakage vortex is observed as the tip clearance increases, and the trajectory of this leakage vortex remains in the same direction along the blade suction side for different tip clearances.
Abstract: Tip clearance between blade end and shroud is inevitable in pump operation and of great importance on pump energy performance and pressure fluctuation. As the tip clearance size increases, the head and efficiency of the mixed flow pump drop accordingly. The simulation results show that the development of a leakage vortex is observed as the tip clearance increases, and the trajectory of this leakage vortex remains in the same direction along the blade suction side for different tip clearances. With the increase in tip clearance size, the intensity of the leakage vortex is enhanced, and the separation between the main leakage vortex and the secondary leakage vortex is also strengthened. The leakage separation angle near the blade tip remains at the same value of 10° for different tip clearance sizes. As for the spectrum analysis, the maximum amplitudes of pressure fluctuations dramatically increase in the impeller when the tip clearance increases from 0.0 mm to 1.0 mm, and the dominant frequencies go from 145 Hz to 184 Hz due to the considerable leakage flow.
102 citations
TL;DR: In this article, the cavitation performance with influence of blade tip clearance for a mix of blades was studied. But the authors did not consider the influence of the geometry of the blade tip.
Abstract: Cavitation phenomenon has strong transient characteristics and is highly influenced by geometric structure. In this study, the cavitation performance with influence of blade tip clearance for a mix...
55 citations
TL;DR: In this paper, the authors investigated the energy performance and radial force of a mixed flow pump with symmetrical and unsymmetrical tip clearance and showed that as the tip clearance increases, the pump head and efficiency both decrease.
Abstract: The energy performance and radial force of a mixed flow pump with symmetrical and unsymmetrical tip clearance are investigated in this paper. As the tip clearance increases, the pump head and efficiency both decrease. The center of the radial force on the principal axis is located at the coordinate origin when the tip clearance is symmetrical, and moves to the third quadrant when the tip clearance is unsymmetrical. Analysis results show that the total radial force on the principal axis is closely related to the fluctuation of mass flow rate in each single flow channel. Unsteady simulations show that the dominant frequencies of radial force on the hub and blade correspond to the blade number, vane number, or double blade number because of the rotor stator interaction. The radial force on the blade pressure side decreases with the tip clearance increase because of leakage flow. The unsymmetrical tip clearances in an impeller induce uneven leakage flow rate and then result in unsymmetrical work ability of each blade and flow pattern in each channel. Thus, the energy performance decreases and the total radial force increases for a mixed flow pump with unsymmetrical tip clearance.
50 citations
TL;DR: In this paper, the influence of tip clearance on pressure fluctuation in a low specific speed mixed-flow pump, along with no tip clearance, was explored, and it was shown that the maximum fluctuation value was located near the guide inlet and impeller outlet, respectively.
Abstract: To explore the influence of tip clearance on pressure fluctuation in a low specific speed mixed-flow pump, tip clearances δ of 0.25 mm, 0.75 mm and 1.00 mm, along with no tip clearance, were selected. The reliability of the simulation was verified by comparison with the experimental data of external characteristics and fluctuation in the guide vane passage. Through ANSYS-CFX, MATLAB code and fast Fourier transform (FFT) algorithm, pressure fluctuation characteristics in this pump were obtained. The results show that pressure fluctuation exists in all conditions due to the rotor-stator interaction. Under the no tip clearance and tip clearance conditions, the maximum fluctuation value was located near the guide inlet and impeller outlet, respectively. Clearance leakage had less influence on pressure fluctuation at the impeller inlet and central regions within a certain range of the clearance; beyond this range, fluctuations in the whole flow passage increased significantly, while the clearance variation had less effect on fluctuation in the guide vane. When the tip clearance value was 1.00 mm, pressure fluctuation of the shroud at the impeller inlet section suddenly increases, which was closely related to the obvious leakage vortexes and a larger low pressure area.
42 citations
TL;DR: In this article, a 3D numerical simulation of an external gear pump was conducted to study the effects of 3D geometrical design parameters on pump performance characteristics such as the flow rate.
41 citations
TL;DR: In this article, a blade squealer tip with cooling holes was numerically computed and validated with the experimental data, and the results showed that, with only tip cooling holes, a lower heat transfer coefficient area can be achieved near the pressure side of cavity floor as increasing the blowing ratio.
40 citations
TL;DR: A microwave sensor-based blade tip timing measurement system with good accuracy is proposed and is compared experimentally with a fiber optic tip timing system to validate the accuracy and show that the system achieves good accuracy.
Abstract: Blade tip timing is an effective method for blade vibration measurements in turbomachinery. This method is increasing in popularity because it is non-intrusive and has several advantages over the conventional strain gauge method. Different kinds of sensors have been developed for blade tip timing, including optical, eddy current and capacitance sensors. However, these sensors are unsuitable in environments with contaminants or high temperatures. Microwave sensors offer a promising potential solution to overcome these limitations. In this article, a microwave sensor-based blade tip timing measurement system is proposed. A patch antenna probe is used to transmit and receive the microwave signals. The signal model and process method is analyzed. Zero intermediate frequency structure is employed to maintain timing accuracy and dynamic performance, and the received signal can also be used to measure tip clearance. The timing method uses the rising and falling edges of the signal and an auto-gain control circuit to reduce the effect of tip clearance change. To validate the accuracy of the system, it is compared experimentally with a fiber optic tip timing system. The results show that the microwave tip timing system achieves good accuracy.
37 citations
TL;DR: In this article, a pumpjet propulsor with different sizes of tip clearances (δ = 0.2, 0.5, 1, 2, 3mm) has been presented to investigate the influence of tip clearance on PJP.
Abstract: Previous studies show that the tip clearance loss limits the improvement of turbomachinery performance, and it is roughly in close relation with the gap size. In this study, a pumpjet propulsor (PJP) with different sizes of tip clearances (δ = 0.2, 0.5, 1, 2, 3mm) has been presented to investigate the influence of tip clearances on PJP. This analysis is based on computational fluid dynamic (CFD) method, and the SST k-ω turbulence model is applied. Calculations are carried out with a worldwide employed ducted propeller (the Ka4-70 propeller in 19A duct) to verify the numerical simulation. And the grid independence validation is discussed. The numerical simulation of PJP flow with different tip clearances is carried out. Results show that the open water efficiency decreases gradually with the increase of tip clearance. The efficiency decreasing is caused by the tip flow loss. The shape of tip vortex of PJP which consisted of tip-separation vortex and tip-leakage vortex is presented. Furthermore, the formation and spread process of tip vortex at different tip clearances are discussed. Then, the effect of different tip clearances on the pressure field of rotor blade is investigated. The main pressure area affected by different tip clearances is mainly concentrated in the area above 0.9 spanwise of the suction side of rotor blade. Beyond that, the effects of different tip clearances on the velocity field of PJP has been studied.
31 citations
TL;DR: In this article, a test rig capable of running at rotational speed 8100 rpm and pressure ratio 1.3 was built according to the simplified model of the labyrinth seal in a compressor stator well (one stage).
30 citations
TL;DR: In this article, numerical investigations of the tip clearance flow characteristics of a pumpjet propulsor based on Computational Fluid Dynamics (CFD) method have been presented The Zwart-Gerber-Belamri (Z-G-B) cavitation model based on Reynolds Averaged Navier-Stokes (RANS) method is employed The structured gird is applied The formation and development of tip clearance flows has been investigated and presented The structure of the leaky vortex has been shown The radial distributions of different velocity components with different Span along the axial direction have
28 citations
TL;DR: In this article, the effect of tip pressure-side geometries on the aerodynamic performance near the tip gap was analyzed at three different cooling-hole arrangements (i.e., no film cooling, only tip holes, and both tip and pressure side holes) and two tip clearances.
TL;DR: In this paper, the effect of five blade tip patterns on performance and acoustics of a twin-stage variable-pitch axial fan is investigated numerically and the best tip pattern is determined by comparing the overall performance under the condition of those patterns carving in stage I impeller, and the performance promotion is then examined under the selected tip grooving in stage II impeller and both two stage impellers.
TL;DR: In this article, an improved filter-based turbulence model based on the density correction and a homogeneous cavitation model were used for implementing this work, and the results showed that when entering into the tip clearance, the backward flow separates from the blade tip near the pressure side, resulting in the generation of a corner vortex with high magnitude of turbulence kinetic energy.
Abstract: The aim of the present investigation is to simulate and analyze the tip leakage flow structure and instantaneous evolution of tip vortex cavitation in a scaled axial-flow pump model. The improved filter-based turbulence model based on the density correction and a homogeneous cavitation model were used for implementing this work. The results show that when entering into the tip clearance, the backward flow separates from the blade tip near the pressure side, resulting in the generation of a corner vortex with high magnitude of turbulence kinetic energy. Then, at the exit of the tip clearance, the leakage jets would re-attach on the blade tip wall. Moreover, the maximum swirling strength method was employed in identifying the TLV core and a counter-rotating induced vortex near the end-wall successfully. The three-dimensional cavitation patterns and in-plain cavitation structures obtained by the improved numerical method agree well with the experimental results. At the sheet cavitation trailing edge in the tip region, the perpendicular cavitation cloud induced by TLV sheds and migrates toward the pressure side of the neighboring blade. During its migration, it breaks down abruptly and generates a large number of small-scale cavities, leading to severe degradation of the pump performance, which is similar with the phenomenon observed by Tan et al. [35].
TL;DR: In this article, a numerical study on blade vibration for the transonic compressor was performed at the Technische Universit€at Darmstadt (TUD) in Germany using a time-linearized approach.
Abstract: This paper presents a numerical study on blade vibration for the transonic compressor
rig at the Technische Universit€at Darmstadt (TUD), Darmstadt, Germany. The vibration
was experimentally observed for the second eigenmode of the rotor blades at nonsynchronous
frequencies and is simulated for two rotational speeds using a time-linearized
approach. The numerical simulation results are in close agreement with the experiment
in both cases. The vibration phenomenon shows similarities to flutter. Numerical simulations
and comparison with the experimental observations showed that vibrations occur
near the compressor stability limit due to interaction of the blade movement with a pressure
fluctuation pattern originating from the tip clearance flow. The tip clearance flow
pattern travels in the backward direction, seen from the rotating frame of reference, and
causes a forward traveling structural vibration pattern with the same phase difference
between blades. When decreasing the rotor tip gap size, the mechanism causing the
vibration is alleviated.
TL;DR: In this article, a series of blade tip geometries, including original plain tip, rounded tip on the pressure side and diverging tip towards the suction side, were adopted to investigate the effect of blade geometry on tip leakage vortex dynamics and cavitation pattern in an axial-flow pump.
Abstract: A series of blade tip geometries, including original plain tip, rounded tip on the pressure side and diverging tip towards the suction side, were adopted to investigate the effect of blade geometry on tip leakage vortex dynamics and cavitation pattern in an axial-flow pump. On the basis of the computation, it clearly shows the flow structure in the clearance for different tip configurations by the detailed data of axial velocity and turbulent kinetic energy. The in-plain trajectory, in aspects of the angle between the blade suction side and vortex core and the initial point of tip leakage vortex, was presented using the maximum swirling strength method. The most striking feature is that the inception location of tip leakage vortex is delayed for chamfered tip due to the change of blade loading on suction side. Some significant non-dimensional parameters, such as pressure, swirling strength and turbulent kinetic energy, were used to depict the characteristics of tip vortex core. By the distribution of circumferential vorticity which dominates the vortical flows near the tip region, it is observed that the endwall detachment as the leakage flow meets the mainstream varies considerably for tested cases. The present study also indicates that the shear layer feeds the turbulence into tip leakage vortex core, but the way is different. For the chamfered tip, high turbulence level in vortex core is mainly from the tip clearance where large turbulent kinetic energy emerges, while it is almost from a layer extending from the suction side corner for rounded tip. At last, the visualized observations show that tip clearance cavitation is eliminated dramatically for rounded tip but more intensive for chamfered tip, which can be associated with the vortex structure in the clearance.
TL;DR: An architecture, based on a trifurcated optic sensor and a hardware processor, that fulfills the need for signal processing during the regular operation of the turbo-engine and allows several sensors to be simultaneously monitored at different points around a bladed disk.
Abstract: Safety and performance of the turbo-engine in an aircraft is directly affected by the health of its blades. In recent years, several improvements to the sensors have taken place to monitor the blades in a non-intrusive way. The parameters that are usually measured are the distance between the blade tip and the casing, and the passing time at a given point. Simultaneously, several techniques have been developed that allow for the inference—from those parameters and under certain conditions—of the amplitude and frequency of the blade vibration. These measurements are carried out on engines set on a rig, before being installed in an airplane. In order to incorporate these methods during the regular operation of the engine, signal processing that allows for the monitoring of those parameters at all times should be developed. This article introduces an architecture, based on a trifurcated optic sensor and a hardware processor, that fulfills this need. The proposed architecture is scalable and allows several sensors to be simultaneously monitored at different points around a bladed disk. Furthermore, the results obtained by the electronic system will be compared with the results obtained by the validation of the optic sensor.
TL;DR: In this paper, the authors used a commercial CFD RANS equation-based solver with the addition of a two-equation turbulence model, in which the numerical solutions were compared with data available in the open literature.
TL;DR: In this article, the influence of tip clearance size on the steady flowfield and aerodynamic damping is assessed for a high-pressure compressor second-stage rotor for an isolated blade passage by imposing the experimental boundary conditions at the inlet and outlet of the passage.
Abstract: The flutter CFD calculations conducted in industry generally use a single-row, single-passage approach with a minimum of detailing to reduce the computational time as much as possible. The question arises of what level of detailing is necessary for accurate aerodamping predictions. In this study, the influence of tip clearance size on the steady flowfield and aerodynamic damping is assessed for a high-pressure compressor second-stage rotor. The steady analyses are conducted on an isolated blade passage by imposing the experimental boundary conditions at the inlet and outlet of the passage. Two operating points are considered: 74 and 100% corrected speed. It is observed that, at the same pressure ratio, the mass flow decreases with a larger tip gap due to the tip clearance flow rolling into a vortex on the blade suction side. Then, unsteady analyses are conducted by enforcing the first torsion mode shape at the corresponding natural frequency. For all interblade phase angles, the same trend is observed: th...
TL;DR: In this paper, the tip leakage flows and related cavitation in the tip region of an axial-flow pump were investigated in detail using the numerical and experimental methods, and the numerical results of the pump model performance were in good agreement with experimental data.
TL;DR: Rotor tip clearance height and the associated tip leakage flow have a significant effect on the performance and stability of compressors as mentioned in this paper, and existing studies considering tip clearance effects on stabler stability are limited.
Abstract: Rotor tip clearance height and the associated tip leakage flow have a significant effect on the performance and stability of compressors. Existing studies considering tip clearance effects on stabi...
02 May 2017
TL;DR: In this paper, the flow through an oxidizer pump in a turbopump was numerically investigated with four different sizes of inducer tip clearances in both non-cavitating and cavitating conditions.
Abstract: A turbopump is used to pressurize propellants to gain high thrust in a projectile and consists of two pumps and a turbine. The pumps usually employ an inducer upstream to prevent performance deterioration by lowering net positive suction head required of the main impeller. However, several types of cavitation and instabilities take place in the flow field. Therefore, numerous experiments and CFD analysis for turbopumps have been conducted. Especially, there were some previous studies on inducer tip clearance, but they were limited to inducer regions due to the complexity of simulating the entire pump. In this study, the flow through an oxidizer pump in a turbopump was numerically investigated with four different sizes of inducer tip clearances. ANSYS CFX 13.0 with Rayleigh–Plesset equation was used to test flows in both non-cavitating and cavitating conditions. In the non-cavitating condition, the pump with the largest inducer tip clearance showed the worst head rise, efficiency and huge size of backflow ...
TL;DR: In this paper, the influence of tip clearance issues in an axial turbine installed to operate as oxidizer booster in the Space Shuttle Main Engine (SSME) was evaluated numerically.
TL;DR: In this article, the influence of tip clearance on the scour rate of pile-supported horizontal axis tidal current turbine (TCT) and also attempts to correlate time-dependent scour depth with the tip clearance.
TL;DR: In this paper, a subsonic axial flow compressor with tip injection was implemented experimentally to understand the underlying flow mechanisms of stability improvement of the compressor with discrete tip injection, and the combination of tip injection with traditional casing treatments was experimentally studied to generate an engineering-acceptable method of compressor stall control.
TL;DR: In this paper, the effects of flow incidence on aerodynamics and heat transfer in the front part of blade tips are bigger than that in the rear part of the blade tips, and flow incidence effects at 0.4% and 1.0% of blade span are investigated.
01 Apr 2017
TL;DR: In this article, the authors investigated the role of the tip clearance flow in the instability in the centrifugal compressor and used ring air jet injection to eliminate the instabilities and to extend the stable flow range of the compressor.
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...
TL;DR: In this article, a linear cascade was fabricated with a nozzle that was set to 65° based on the axial direction, and a blade row was designed to be movable along the pitchwise direction in order to investigate flow characteristics as a function of blade movement.
TL;DR: In this paper, a prototype optical fiber measurement system was built and tested based on the rotor test rig, which consists of the reflective intensity-modulated optical fiber bundle (sensor), main signal processing unit, high-speed data acquisition card, and a computer.
Abstract: The benefits of reducing the tip clearance have been receiving many scholars’ attention all the time, which bring turbine efficiency increasing, emissions reduction, payloads increasing, and mission range abilities extension. In order to gain the blade tip clearance dynamically, a prototype optical fiber measurement system was built and tested based on the rotor test rig. The optical fiber tip clearance measurement system consists of the reflective intensity-modulated optical fiber bundle (sensor), main signal processing unit, high-speed data acquisition card, and a computer. The static performance and dynamic performance experiments were conducted to verify the performance of the system we designed. In addition, the results show that the accuracy of the system is 25 μm or better; the stability of the measurement system was evaluated in room temperature. The clearance measurement range is about 5 mm, and sensitivity of the sensor is 0.0733/mm. Furthermore, the typical tip clearance dynamic measurement experiment results show that the system has good dynamic response characteristics as well. The system will provide a new tool for engine health monitoring or fast active tip clearance control.
17 Aug 2017
TL;DR: In this article, the rotor failure caused by flutter is a major problem in the last stage of modern steam turbines and it is because rotor at this stage always has a large scale in spanwise, which provides low structural...
Abstract: Blade failure caused by flutter is a major problem in the last stage of modern steam turbines. It is because rotor at this stage always has a large scale in spanwise, which provides low structural ...