Blade Tip Area Research Articles

Research on the flow and heat transfer performance of variable geometry high-pressure turbine blade tip area of gas turbine

Research on the flow and heat transfer performance of variable geometry high-pressure turbine blade tip area of gas turbine

Three-dimensional optimization of squealer-tip for a transonic axial-flow compressor rotor blade

This research represents an innovative method for geometry generation of the squealer-tip in axial compressor rotors and its exploit in a numerical optimization process to obtain a better stage performance. For this purpose, the NASA Rotor-67 transonic compressor rotor blade is used as a test case to study the aerodynamic performance using computational fluid dynamics. The validation was performed for the characteristic map at the design speed and the comparison with the experimental results indicates excellent matching and high adaptability of the numerical method. An ingenious method of producing squealer tip for an axial compressor rotary blade is presented in this article, which is capable for locally shaping both suction and pressure surface geometry at a desired spanwise location simultaneously, while keeping the tip clearance at its value of the baseline NASA Rotor-67 geometry. In this method, control points are used to produce the starting spanwise location of the squealer, and modify the depth of the squealer geometry. The L-27 orthogonal array of the Taguchi method as the Design of Experiment (DOE) has been used to investigate the sensitivity of the aerodynamic results in three performance points of the choke, design and near stall regions, in relation to the design variables of the squealer. The generated database in the sensitivity analysis was used to train artificial neural networks to replace the CFD solutions with overwhelming run time. By coupling the genetic algorithm to the aforementioned neural networks and by applying penalties to maintain the minimum performance of the Rotor-67, enhancement of total pressure ratio, adiabatic efficiency, mass flow rate and even the surge margin was achieved. The main effect of the squealer is to modify the shape of blade tip vortices, and by more dissipation of energy in blade tip area and reduced equivalent flow area in this region, finally results in improved overall mass flow rate, total pressure ratio, adiabatic efficiency and surge margin by 0.58 %, 0.36 %, 0.19 % and 4.81 % respectively, at design point.

Study on flow characteristics of leakage in the last stage inner blade tip clearance of steam turbine

Internal steam leakage in steam turbines from the high-pressure side to the low-pressure side through clearances causes loss, resulting in reduced efficiency and potentially compromising the safe operation of the turbine. Therefore, a comprehensive understanding of the flow characteristics of leakage through blade tip clearances is crucial to improve the efficiency of steam turbines. In this paper, the last stage blades of the low-pressure cylinder of a certain 600 MW ultra-supercritical steam turbine unit were studied. A wet steam flow model and a turbulence model were established, and the flow characteristics of the last stage under different inlet parameters, outlet parameters, and tip clearance sizes were analyzed. The results showed that an increase in the clearance size affects the inlet and outlet steam angles of the rotor blades, with significant changes occurring near the blade tip. The main flow velocity inside the rotor blade channel fluctuates violently starting from the 70% axial position. The high entropy region is located near the exit flow region of the rotor blade, with its range expanding as the clearance size increases. The entropy change is significant at 60% blade height and above, with more intense changes occurring in the blade tip area. The relative leakage amount and efficiency change uniformly with clearance variation. Generally, for every 0.1% increase in clearance height, the relative leakage amount increases by ∼0.31%–0.42%, and the stage efficiency decreases by 0.34%–0.44%. The results of this study can provide a theoretical basis and guidance for improving the flow efficiency of steam turbines.

Effect of blade tips ice on vibration performance of wind turbines

There are abundant wind resources in cold regions. Therefore, it is essential to systematically study some icing situation of wind turbines blades (especially the blade tip area) to reduce the loss of wind turbines blades caused by faults, which has important significance to the development and utilization of superior wind power resources in alpine regions in the future. An S8025 airfoil blade was used as this research object to research this influence of different loads on this typical vibration performance of a wind turbines with blade tip icing. The results display that the tip area of these wind turbines will be covered with ice because of the small chord length. Blade tip icing results in an increase in blade mass, blade stiffness, blade torsional stiffness, and other parameters, and the low-order vibration frequencies decreases while the high-order vibration frequencies increases. The centrifugal force load significantly affects the vibration performance of a wind turbines with blade tip icing. The results can be used as a reference to improve the deicing of wind turbines blade tips.

Numerical study of the effect of Inlet paired Swirl on Performance and Stability of Axial compressor

In order to study the effect of inlet paired swirl distortion on the performance and stability of compressor, a full-annulus unsteady numerical simulation of the effects of swirl distortion on performance and stability of transonic rotor Rotor 37 is carried out in this paper. The result shows that: the rotor performance deteriorates and the stable working range decreases under the effect of vortex flow distortion; the circumferential side flow caused by vortex swirl distortion leads to the uneven circumferential distribution of flow parameters at the inlet and the outlet of the compressor; the rotor blade has a very significant attenuation effect on the swirl distortion, and the swirl distortion intensity decreases along the axial direction; the circumferentially inhomogeneous distribution of rotor angle causes excessive local aerodynamic load on the rotor, and high intensity leakage vortices and excitation vortices are generated at the blade tip. The circumferentially unevenly distributed swirl angle causes excessive local aerodynamic load of the rotor, resulting in high-intensity leakage vortex and shock wave interference in the blade tip area, which severely blocks the flow path and eventually leads to unstable flow in the Rotor37.

Study on Structural Performance of Horizontal Axis Wind Turbine with Air Duct for Coal Mine

Considering the characteristics of narrow underground space and energy distribution, based on blade element momentum theory, Wilson optimization model and MATLAB programming calculation results, the torsion angle and chord length of wind turbine blade under the optimized conditions were obtained. Through coordinate transformation, the data were transformed into three-dimensional form. The three-dimensional model of the blade was constructed, and the horizontal axis wind turbine blade under the underground low wind speed environment was designed. The static structural analysis and modal analysis were carried out. Structural design, optimization calculation and aerodynamic analysis were carried out for three kinds of air ducts: external convex, internal concave and linear. The results show that the velocity distribution in the throat of linear air duct is relatively uniform and the growth rate is large, so it should be preferred. When the tunnel wind speed is 4.3 m/s and the rated speed is 224 rad/s, the maximum displacement of the blade is in the blade tip area and the maximum stress is at the blade root, which is not easy to resonate. The change rate of displacement, stress and strain of blade is positively correlated with speed. The energy of blade vibration is mainly concentrated in the swing vibration of the first and second modes. With the increase in vibration mode order, the amplitude and shape of the blade gradually transition to the coupling vibration of swing, swing and torsion. The stress and strain of the blade are lower than the allowable stress and strain of glass fiber reinforced plastics (FRP), and resonance is not easy to occur in the first two steps. The blade is generally safe and meets the design requirements.

Energy Efficiency Optimization Design of a Forward-Swept Axial Flow Fan for Heat Pump

As one of the key components of the heat pump system, compared to that of a conventional axial fan, the blade tip area of a forward-swept axial fan is much larger than its blade root, which is the main noise source of the fan and also has an important influence on the fan efficiency. Enhancement of the aerodynamic performance and efficiency of a forward-swept axial fan was addressed by utilizing the Bezier function to parameterize the forward-swept curve on blade tops. In order to quickly select an agent model suitable for the project, an ES model was established by integration of the radial basis function model and the Kriging model. When NSGA-II was combined, multi-objective optimization was carried out with the flow rate and total pressure efficiency as optimization goals. Analysis of optimization results revealed that the optimized axial flow fan’s flow rate and total pressure efficiency were improved to some degree. At the design working point, the fan’s flow rate increased by 1.78 m³/min, while the total pressure efficiency increased by 3.0%. These results lay solid foundation for energy saving of the heat pump system.

Lock-in phenomenon of tip clearance flow and its influence on aerodynamic damping under specified vibration on an axial transonic compressor rotor

In this study, the lock-in phenomenon of Tip Clearance Flow (TCF) instabilities and their relationship to blade vibration are investigated numerically on an axial transonic rotor with a large tip clearance. The capabilities of simulating instability flow and lock-in phenomenon are verified on a transonic rotor and a NACA0012 airfoil by comparing with the test data, respectively. The lock-in phenomenon is first numerically confirmed that may occur to TCF instabilities when its frequency is close to the blade vibration frequency. The lock-in region becomes wider with the vibration amplitude increasing, and it is also affected by modal shapes. For the rotor at the simulation conditions in this study, the bending mode results in a wider lock-in region than the torsional mode. In the lock-in region, the phase difference between the Tip Clearance Vortex (TCV) and the blade vibration changes with the flow condition and the frequency ratio of the blade vibration and the TCV instabilities. The frequency of the TCV instabilities reduces with the mass flow decreasing. Therefore, reducing mass flow and increasing frequency ratio have similar effects on the TCV phase, which causes a significant variation on the unsteady pressure amplitude in the blade tip area. Thus, the aerodynamic damping changes significantly with the TCV phase. The aerodynamic damping displays a nonlinear relationship with the vibration amplitude, and it changes from negative to positive with the vibration amplitude increasing at the same frequency ratio. The negative damping is mainly provided by the tip area of the blade. For unlocked conditions, the period of the TCF instabilities fluctuates over time, and it cannot be directly separated by their frequency features. Inter Blade Phase Angle (IBPA) also has an important influence on the feature of the TCV instabilities. The occurrence of frequency lock-in also requires “appropriate” IBPA. For the examined working conditions, the frequency lock-in occurs under 0 ND (Nodal Diameter), but not under 8 ND. However, no matter 0 ND or 8 ND, the phase of TCV always locks onto the IBPA at the examined conditions.

Analysis of near stall condition of high bypass fan rotor based on airworthiness certification

In order to ensure flight safety, the near stall condition test is one of the most important steps in the airworthiness certification phase of civil aircraft. The twisted and swept fan is one of the most important components of the high bypass ratio engine. The unsteady flow field of the fan rotor was calculated by CFD simulation. The unsteady flow at the tip of blades is an important cause of the development of the fan rotor from near stall condition to stall condition. Dynamic mode decomposition method (DMD) was applied to analysis unsteady flow field of the blade tip area. And compressed sensing dynamic mode decomposition (CPDMD) method was tried to deal with massive grid based on dynamic mode decomposition method. The dynamic mode decomposition method successfully separates the flow structure of the unsteady flow field. The compressed sensing dynamic mode decomposition method compresses the initial flow field snapshot to obtain low-dimensional flow field data. Then the DMD modality is got by analyzing the low-dimensional flow field. Finally, the DMD mode with the initial flow field snapshot dimension is obtained. So the CPDMD method effectively reduces algorithm runtime and reduces the computational resource requirements. This provides the possibility to process a large amount of flow field data that would otherwise be impossible to process.

Effect of blended blade tip and winglet on aerodynamic and aeroacoustic performances of a diagonal fan

Tip clearance flow significantly influences the aerodynamic and aeroacoustic performances of a fan. Its mechanism and control have remained a hotspot in the field of turbomachinery. In this paper, blended blade tip and winglet (BBTW) technology is proposed based on the combination of blended blade and end wall and winglet technologies, while the flow field and sound field of an original blade and the BBTW-blade of a diagonal fan are numerically simulated. The calculation results show that the BBTW design reduces the pressure difference between the suction surface and the pressure surface in the blade tip area and enhances the necking effect of tip clearance, thus inhibiting tip clearance leakage flow and improving the aerodynamic performance of the diagonal fan. In addition, as BBTW weakens the tip leakage vortex intensity, thereby reducing the sound pressure level of the near-field and the far-field noise.

Study of the Affinity Law of Energy and Cavitation Characteristics in Emergency Drainage Pumps at Different Rotating Speeds

The affinity law is widely used in pump design and experiments. The applicability of the affinity law in an emergency drainage pump at different rotating speeds was studied. Experiments and numerical simulation through ANSYS CFX (Computational Fluid Dynamics X) 15.0 software were used to research the affinity law characteristics. Results show that the simulation of characteristics is basically consistent with the experimental curves. In small flow rate conditions, due to the existence of obvious differential pressure between the pressure side and the suction side in the impeller blade tip area, the leakage flow occurs at the tip clearance, which collides with the main stream at the inlet and generates vortices at the leading edge of the impeller. The tip leakage flows of the pump at four different rotating speeds were compared, and it was found that the tip leakage increased with increasing rotation speed, and at the same rotation speed, the tip leakage flow was large in the small flow rate condition, which led to the simulation value of the characteristics being greater than the scaling value. As the flow rate increased, the anti-cavitation performance of the pump became worse and the hydraulic loss was larger, so the pump’s performance curve deviated from the scaling curve.

Fluid-structure interaction study of a mixed-flow pump impeller during startup

PurposeThe purpose of this paper is to experimentally and numerically study the transient hydraulic impact and overall performance during startup accelerating process of mixed-flow pump.Design/methodology/approachIn this study, the impeller rotor vibration characteristics during the starting period under the action of fluid–structure interaction was investigated, which is based on the bidirectional synchronization cooperative solving method for the flow field and impeller structural response of the mixed-flow pump. Experimental transient external characteristic and the transient dimensionless head results were compared with the numerical calculation results, to validate the accuracy of numerical calculation method. Besides, the deformation and dynamic stress distribution of the blade under the stable rotating speed and accelerating condition were studied based on the bidirectional fluid–structure interaction.FindingsThe results show that the combined action of complex hydrodynamic environment and impeller centrifugal force in the startup accelerating process makes the deformation and dynamic stress of blade have the rising trend of reciprocating oscillation. At the end of acceleration, the stress and strain appear as transient peak values and the transient effect is nonignorable. The starting acceleration has a great impact on the deformation and dynamic stress of blade, and the maximum deformation near the rim of impeller outlet edge increases 5 per cent above the stable condition. The maximum stress value increases by about 68.7 per cent more than the steady-state condition at the impeller outlet edge near the hub. The quick change of rotating speed makes the vibration problem around the blade tip area more serious, and then it takes the excessive stress concentration and destruction at the blade root.Originality/valueThis study provides basis and reference for the safety operation of pumps during starting period

水平軸風車翼端流れに関する実験的研究

The surface flow on a rotor blade of a horizontal axis wind turbine (HAWT) has complicated three-dimensional flow with span-wise velocity. This paper’s aim is to clarify the flow field around wind turbine blades. The measurement was performed on a model wind turbine with three blades using a laser doppler velocimeter (LDV) in a wind tunnel in order to clarify the three-dimensional flow field around the rotor blade tip experimentally. It can be seen that the amount of circulation due to the influences of the blade tip vortex is reduced in the blade tip area. The blade tip vortex is moved to the outside in the radial direction due to the influence of the expansion of the wake.

Coat weight control in bent blade mode

Bent blade metering is the most common method used in board coating. As board machine speeds today have increased, new requirements have been set on blade geometry and accuracy of blade adjustments. A good understanding of the blade parameters and physical phenomena around the blade tip area is, therefore, necessary. Automatic coat weight profile adjustment using feedback from the coat weight measurement system is a great tool to improve the cross-direction coating uniformity and reel condition. In bent blade coating, however, the parameters for adjusting the cross-direction profilers need to be modified from those used in stiff blade coating. At high board coating speeds with bent blade, good coat weight control will require tuning of the blade parameters. To be able to reach a given coat weight at a high speed with a low tip angle, a high mechanical force is needed to control the high dynamic forces that are created in the blade tip area. The mechanical force can be increased either with a thicker blade or with a shorter free stick-out (i.e., shorter distance between the blade support bar and the blade tip). A higher tip angle can be used to decrease the dynamic forces to keep the coat weight in target; however, coating coverage and uniformity of the coating layer will then be reduced. Furthermore, blade wear is more severe at higher tip angles. For cross-direction profiling, a shorter free stick-out is suggested as a better approach than use of a thicker blade. The coat weight profile response and accuracy improves with a shorter stick-out as thinner blade with more flexibility can be used. Three alternative coat weight control methods for bent blade operation are discussed: blade load adjustment, beam angle adjustment, and load adjustment at constant tip angle. For effective coat weight cross-direction controls, the blade operating mode and parameters need to be chosen in accordance with the speed and coat weight range at which the coater is operating.

Flow Physics and Profiling of Recessed Blade Tips: Impact on Performance and Heat Load

In axial turbine, the tip clearance flow occurring in rotor blade rows is responsible for about one-third of the aerodynamic losses in the blade row and in many cases is the limiting factor for the blade lifetime. The tip leakage vortex forms when the leaking fluid crosses the gap between the rotor blade tip and the casing from pressure to suction side and rolls up into a vortex on the blade suction side. The flow through the tip gap is both of high velocity and of high temperature, with the heat transfer to the blade from the hot fluid being very high in the blade tip area. In order to avoid blade tip burnout and a failure of the machine, blade tip cooling is commonly used. This paper presents the physical study and an improved design of a recessed blade tip for a highly loaded axial turbine rotor blade with application in high pressure axial turbines in aero engine or power generation. With use of three-dimensional computational fluid dynamics (CFD), the flow field near the tip of the blade for different shapes of the recess cavities is investigated. Through better understanding and control of cavity vortical structures, an improved design is presented and its differences from the generic flat tip blade are highlighted. It is observed that by an appropriate profiling of the recess shape, the total tip heat transfer Nusselt number was significantly reduced, being 15% lower than the flat tip and 7% lower than the base line recess shape. Experimental results also showed an overall improvement of 0.2% in the one-and-a-half-stage turbine total efficiency with the improved recess design compared to the flat tip case. The CFD analysis conducted on single rotor row configurations predicted a 0.38% total efficiency increase for the rotor equipped with the new recess design compared to the flat tip rotor.