Side Of Blade Research Articles

Numerical investigation of alleviation of undesirable effect of inter-blade vortex with air admission for a low-head Francis turbine

In order to compensate for the stochastic nature of the power grid due to the tremendous development and the integration of renewable energy resources and meet its other requirements, the hydraulic turbines are forced to operate more frequently under partial load conditions with singular and misaligned flows inevitably excited by the inter-blade vortex. This paper presents numerical investigations of the unsteady characteristics of the inter-blade vortex for a low-head model Francis turbine. The SST k - ω turbulent model is used to close the unsteady Reynolds-averaged Navier-Stokes (RANS) equation. The flow structure of the inter blade vortex predicted by the numerical simulation is confirmed by experimental visualizations. It is shown that the total vortex volume in the runner sees a quasi-periodical oscillation, with significant flow separations created on the suction side of the runner blade. A counter measure by using the air admission into the water from the head cover is implemented to alleviate the undesirable effect of the inter-blade vortex. The analyses show that the development of the inter-blade vortex is significantly mitigated by the injecting air that controls and changes the spatial distribution of streamlines. Furthermore, the flow aeration with a suitable air flow rate can reduce the energy dissipation caused by the inter-blade vortex and plays a critical role in preventing the excessive amplitudes of the pressure fluctuation on the suction side of the runner blade. This investigation provides an insight into the flow mechanism underlying the inter-blade vortex and offers a reference to alleviate and mitigate the adverse consequences of the inter-blade vortex for the Francis turbine.

Over Speed Protection of Horizontal Axis Wind Turbine Using Slot in the Turbine Blade

The wind energy is more reliable, clear, and easilyexploitable form of renewable energy source. Wind turbines are being stationed to capture the wind’s power and convert it to electricity. The wind turbines are operated at rated speed to ensure smooth operation. When the wind turbine faces the higher wind speed, wind forceimpacts the tower head causing immediate damage the turbine blade. Wind turbines are equipped with various Aerodynamic braking systems and mechanical braking system to control the over speeding of the wind turbine rotor at extreme wind velocity. In this novelmethodology, it is attended to reduce the rotational speed of the wind turbine aerodynamically by providing the chord wise slot (opening). The slot modifies the pressure distribution over the upper side and lower side of the turbine blade that slows down the rotational speed of the wind turbine within the safe limit. In this present attempt, the over speeding of the wind turbine rotor is effectively controlled without disturbing the power generation. The different parameters of the slot such as the position of the slot, inclination of the slot, and width of the slot are studied and the slot parameters are computationally optimized.

Numerical research of the influence of the geometric parameters of shadowing fins on the intensity of jet cooling by supercritical carbon dioxide

This paper discloses computer simulation results of thermos-hydraulic processes in cooling channels of carbon dioxide turbines used in oxy-fuel power production facilities. Stream cooling systems may be modified by the installation of shadowing ribs on the pressure and suction sides of a hollow blade and this intensifies heat transfer and reduces the cooling agent flow. The heat transfer maximal intensity is obtained at the distance between deflector orifice and shadowing fin of 0.25 orifice diameter. Change of the shadowing fin cross-section shape from oval to circular causes increases of the channel hydraulic resistance for 20–28% and the mean Nusselt number for 8–25%.

Numerical Investigation of the Hydrodynamic Performance of the Propeller Behind the Ship with and Without Wed

Abstract The presented paper numerically carries out the investigation of the hydrodynamic performance of the propeller behind the ship with and without wake equalizing duct (WED). It is mounted in front of the propeller in order to equalize the ship’s wake flow and improve the propeller performance. The computational fluid dynamics (CFD) analysis software STAR-CCM solver was adopted to simulate the KP505 propeller behind the KRISO container ship (KCS) using overlapping grid technology and user-defined functions. To obtain the effect of a –duct on propeller performance, the ship bare hull case, the with-propeller case, and the with-propeller-and-duct case are also computed. Together, these computations provide for a –complete CFD comparison of the duct effects. Also, the Taguchi design of the experiment method is applied to investigate three parameters (angle of attack, trailing edge radius, and chord length) of the duct. Finally, the main dimensions are obtained, and the thrust and torque coefficients are presented and discussed for one blade and whole blades during one cycle. Based on the numerical results, it is indicated that good design increases efficiency by 1.67%, and a –bad design may reduce efficiency by 3.25%. Also, the effect of the WED caused to decrease the pressure pulse by 35.9% in the face side of the propeller blade.

Film cooling simulation on an entire gas turbine blade with square pulsed coolant injection

Film cooling is an effective method to keep the gas turbine blades from high temperature gases and thermal stresses. Square pulsating film cooling on different sections of a modified NASA C3X blade is numerically investigated. Temperature distribution and film cooling performance are investigated for various blowing ratios of 0.5, 0.75, 1.0, 1.5, 2 and 2.5 in pulse frequency of 50Hz. Reynolds-Averaged Navier-Stokes equations for steady and pulsating injection considered. The shear stress transport ( ) model applied for turbulence effects. Simulations are performed using finite volume method. Obtained results show different findings of pulsating film cooling on the various blade surfaces. For large blowing ratios, averaged pulsed film covering effectiveness at leading edge and pressure side of blade is reduced compared to small and middle values of blowing ratios. This trend is reversed in the suction side. Reynolds number of mainstream has the maximum effect on film effectiveness distribution on pressure section. The averaged centerline pulsed film coolant performance on the pressure surface and leading edge at blowing ratio of 0.5 and for suction side at blowing ratio 2.5 was maximum.

Wind Tunnel Test of a Rotorcraft with Lift Compounding

Rotorcraft flight speed is limited by compressibility effects on the advancing blade side and decreasing lift potential on the retreating blade side. It may thus be beneficial to employ a hingeless rotor to generate additional lift with the advancing blade and compensate the resulting rolling moment with a fixed wing on the retreating blade side. This concept is a form of "lift compounding" that appears to show enormous potential. The present paper presents results of a wind tunnel test with a slowed, hingeless rotor and single fixed wing on the retreating blade side. Based on rotor test stand data and flow field measurements, the impact of operational and rotor parameters on system performance and aerodynamics is examined, mutual interaction effects between rotor and fixed wing are analyzed, and dominant flow structures are characterized in the reverse flow region on the retreating blade side. Flow field analysis reveals a reverse flow entrance vortex that freely convects through the reverse flow region and rivals the blade tip vortices in strength. Contrary to previous beliefs, this vortex originates from upstream of the reverse flow region and only its detachment from the rotor blade is related to entering this region. The combination of finite rolling moment trim and aft shaft tilt significantly increases rotor lift coefficient and corresponding peak lift-to-drag ratio of the compound rotorcraft. Results are compared with predictions from a comprehensive rotor analysis that is expanded to cover the main effects of the added fixed wing and is able to reproduce general performance trends of the rotorcraft. The present study highlights that adding a single fixed wing and hingeless rotor to a high-speed rotorcraft could significantly improve its performance.

Surface Curvature Effects on Film Cooling Performance for Shaped Holes on a Model Turbine Blade

Abstract Surface curvature has been shown to have significant effects on the film cooling performance of round holes, but the literature include few studies of its effects on shaped holes despite their prevalence in gas turbines. Experiments were performed using two rows of holes placed on the suction side of a scaled-up turbine blade in a low Mach number linear cascade wind tunnel with low freestream turbulence. The rows were placed in regions of high and low convex surface curvature. Geometries and flow conditions for the rows were matched to those from previous flat plate studies. Comparison of the adiabatic effectiveness results from the high curvature and flat plate rows revealed the same trends as those in the literature using round holes, with increased performance for the high curvature row at lower blowing ratios and the opposite at higher ones. The low curvature row had similar performance to the flat plate row at lower blowing ratios, suggesting the mild convex curvature had little beneficial effect. At higher blowing ratios, the low curvature row had inferior performance, which was attributed to the local freestream adverse pressure gradient that generated additional turbulence, promoting jet-to-mainstream mixing and decreasing performance.

Slowed Hingeless Rotor Wind Tunnel Tests and Validation at High Advance Ratios

In forward flight, slowing down a rotor alleviates compressibility effects on the advancing side blade tip, extending the cruise speed limit, and inducing high-advance-ratio flight regime. Previous wind tunnel tests have shown that an articulated rotor trimmed to zero hub moment generates limited thrust at high advance ratios, because the advancing side needs to be trimmed against the retreating side with significant reverse flow, where the rotor is ineffective in generating thrust. A rigid hingeless rotor with lift offset may help overcoming this problem. A series of wind tunnel tests were conducted to investigate the behavior of slowed hingeless rotors at high advance ratios. Performance, control angles, hub vibratory loads, and blade structural loads were measured and compared with comprehensive analysis predictions. The results demonstrate that a hingeless rotor with lift offset is more efficient in generating thrust and exhibits higher lift-to-drag ratio at high advance ratios. The blade structural load level is significantly higher compared with an articulated rotor, especially its flap bending moment, which can pose a critical structural constraint on the rotor.

Mechanical properties of helical milling deep hole on QFRP using cryogenic cooling process

The structure and physical properties of quartz fiber reinforced polyimide composite (QFRP) lead to the milling hole defects of crimp, ablation and delamination, as well as serious tool wear and limited hole making depth. Based on three kinds of defects of helical milling holes of composite materials, the cutting force model was constructed considering the cutting micro-zone temperature. This article presents the first comprehensive investigation on cryogenic (83K) milling deep hole process of QFRP through liquid nitrogen injection by carbide film blades with 10 mm cutting diameter. In this project, the surface morphology, cutting force, cutting temperature and tool wear performance were analyzed compared with dry milling ones. The results show that the three kinds of defects are all affected by cutting force and mechanical properties of composites. In dry milling shallow hole with low speed, the type I crimp defect of hole entry, the type II lamination defect of hole middle and exit are all serious, as well as the type III ablative defect of hole exit with 1.06 mm machining error at high speed. The milling hole cutting forces are mainly related to axial feed, tangential feed and composite properties considering temperature. At the same time, the axial and tangential forces are more affected by the change of tool axial feed than tangential feed. After cryogenic cooling intervention, milling hole defects and tool wear are well inhibited. And the accuracy of shallow hole was up to 0.03 mm at hole exit, as well as 0.05 mm for deep hole without delamination tear and ablation defects. Conclusion, the properties change of matrix and composite at low temperature are the main reason for preventing type I and II milling hole defects, and the eliminated passivation and adhesion of tool side blade and flank surface are the reasons for restraining type III defects.

Numerical investigations of flow characteristics of a pumpjet propulsor in oblique inflow

In this study, a detailed analysis of hydrodynamic performance of a pumpjet propulsor (PJP) in different oblique inflow angles (β=0⁰, 5⁰, 10⁰, 15⁰, 20⁰, 25⁰, 30⁰, 40⁰) and different rotational speeds (n=3000rpm, 3600rpm, 4200rpm) is investigated numerically. The SST k-ω turbulence model and sliding mesh technology based on the Reynolds Averaged Navier-Stokes (RANS) method are employed. The structured grids are adopted to the whole computational domain. The grid independent inspection is carried out and verified. A ducted propeller (the Ka4-70 propeller in 19A duct) is selected to validate the numerical method by comparison of its results with experimental data. Based on the numerical method, it can be found that the propulsor efficiency decreased with the increasing of different β. The propulsor efficiency changes tinily in little oblique angle and decreases significantly when the oblique angle is larger than 20⁰. The thrust coefficient and torque coefficient of PJP are obtained. The increase of β has a negative impact on the balance performance of PJP. The pressure distributions of pressure and suction side of rotor blade with different β are analyzed. Owing to the influence of β, the pressure of the upper left region of rotor blade drops significantly. The enlargement of the local load on pressure side and the appearance and expansion of the low-pressure region on suction side occour at the bottom right region of rotor blade. The radial distributions of the axial velocity (Vz) and the tangential velocity (Vt) with different Span and β along the axial direction are investigated. The increase of β resultes in a severe oscillatory behavior of the flow velocity, which easily induces the occurrence of cavitation phenomenon and mechanical vibration. The velocity contours of the axial cross section with different β are presented. Due to the change of β, the flows are blocked by the flow-guide and duct, there are obvious high-velocity and low-velocity regions of the flows.

Numerical Analysis of High-Altitude Inlet Air on Boundary Layer Flow Loss in an Aero-Engine Compressor

A numerical analysis is performed to explore the high altitude and high Mach flight on the effect of wall boundary layer loss in the compressor. The accuracy for solution results by the application of the similarity criterion and parameter definition of the air inlet is compared with the existing experimental test result. The results indicate that the radial adverse pressure gradient in the rotor domain gradually increases along the span direction and decreases as flight Mach number increases; meanwhile, the circumferential adverse pressure gradient on the pressure side of the rotor blade is correspondingly larger and less than that on the suction side. In particular, the entropy increase along the streamwise shows a decreasing trend and an increasing trend inside the hub and shroud wall boundary layers, respectively. At 2.1 Ma, the entropy increase in the rotor domains enhances by 24.36–27.80% inside the shroud boundary layer, relative to the hub boundary layer; however, it decreases by 0.97–8.54% in the stator domain. With the increase in flight Mach number from 2.1 to 3.4, the average entropy increase reductions in the rotor domain decrease by 18.99–24.97% within the hub boundary layer and 5.71–8.1% within the shroud boundary layer. In the stator domain, it drops by 18.45–9.03% inside the hub boundary layer and 6.88–8.67% inside the shroud boundary layer. It was therefore found that, as Mach number increases from 2.1 to 3.4, the entropy increase reduction is larger inside the hub boundary layer than inside the shroud boundary layer.

Numerical investigation on the effects of leakage flow from Guide vane-clearance gaps in low specific speed Francis turbines

Clearance gap in guide vanes of Francis turbine induces the leakage vortex. This vortex flow interacts with the main flow and leads to the instability in the fluid flow pattern and eventually deteriorates the performance of the turbine. In this study, the detailed numerical examination of the unsteady flow due to leakage vortex and influence of this in the performance of turbine is carried out using time dependent numerical analysis. The numerical simulation is carried out using SST turbulence model with numerical validation. The development of leakage vortex is studied within the clearance gap region. Time dependent numerical simulation is carried out to investigate the growth and vortex propagation considering five revolutions of the runner. Results shows that the leakage vortex travelling form the guide vane clearance gaps influence the performance of the runner. On analysing the leakage vortex path, it is seen that the vortex travels from the pressure side of runner blade to the suction side of adjacent blade opposite to the runner rotation. Furthermore, this leakage vortex is carried down to the draft tube where the vortex rope seems to grow up to 50% geometric progression of draft tube cone and gradually decreases before reaching the elbow. Upon investigation of resulting torque and head during runner rotation, the periodic variation of torque and head can be seen, however with different phase. This is inferred to be the influence of leakage vortex that travels along with the main flow.

CFD analysis of horizontal axis wind turbine braking system using chordwise spacing

Wind energy is an environment- friendly and efficient source of renewable energy to meet the growing demand for energy. The wind turbines are designed to operate at rated wind speed. The sudden wind acceleration and wind gusts can overload the tower head causing immediate damage to the mechanical drive train shaft, gearbox, and turbine blade. The various aerodynamic braking systems are presently used to control the rotational speed of the wind turbine at extreme wind velocity. In this proposed approach, it is attempted to control the over speeding of the wind turbine aerodynamically by providing the chord wise spacing (slot) on the blade. The spacing provided on the blade alters the pressure distribution between the pressure side and the suction side of the turbine blade that brings down the rotational speed of the wind turbine within the allowable limit. In this approach, the over speeding of the wind turbine blades is effectively controlled without affecting the power generation. The primary parameter of the spacing i.e. chord wise position of the spacing is computationally analyzed.

Distribution and motion characteristics of bubbles in a multiphase rotodynamic pump based on modified non-uniform bubble model

Multiphase rotodynamic pumps are important equipment that transport gas-liquid mixtures in offshore oilfields, suggesting it is necessary to investigate the flow characteristics in such pumps. In this study, the Eulerian two-fluid model is solved to obtain the bubble distribution in the pump, while the non-uniform bubble model is used to predict the break-up and coalescence of bubbles. The gas cavity equation is introduced to capture the rapid coalescence of bubbles near the suction side of the impeller blades, and the interphase forces in the cavities are modified. Compared with the experimental measurements for the gas volume fraction and bubble size, it is found that the simulations with the modification have better accuracies than without it. The effects of the inlet gas volume fraction (IGVF) on the bubble distribution are analyzed. Due to the formation of vortices, a large bubble number density is observed near the shroud of the impeller inlet, which increases with greater IGVF. The gas-liquid separation in the diffuser becomes more significant as the IGVF increases. Bubbles from the impeller inlet are observed to continuously gather near the suction side of the impeller blades. This forms a gas cavity that moves towards the impeller outlet with a low gas volume fraction. The rotor-stator interactions cause the air pockets to discontinuously move along the pressure side of the diffuser blade.

Numerical investigation on inter-blade cavitation vortex in a Franics turbine

Inter-blade cavitation vortex is substantially considered as a particular cavitation flowing phenomenon associated with liquid transportation in Francis turbine. It causes several adverse effects on the pressure and velocity fields and cannot be eliminated by hydraulic design or optimization. This paper presents the numerical and experimental investigations on cavitation fluid for a reduced scale model of Francis turbine. The inter-blade cavitation vortex structure predicted by numerical simulation yields a very good validation against the experimental visualization. The vapor volume caused by cavitation flowing oscillates periodically and is accompanied by the precessing frequency of inter-blade vortex that is equivalent to the rotational frequency of the runner. Flow separation induced by negative incident angle at the leading edge of runner is identified as the main reason for the incipient and development of the inter-blade cavitation vortex. Cavitation-vortex interaction analysis in terms of the relative vorticity transport equation evidently shows that the vortex stretching term and Coriolis force term always significantly influence the vorticity production near the suction side of the runner blades while the dilatation term and baroclinic torque term play decisive roles on vorticity development adjacent to the vortex center.

Methyl jasmonate induces leaf senescence of Ginkgo biloba L.: relevance to endogenous levels of plant hormones

Methyl jasmonate (JA-Me) applied to the abaxial side of the middle of leaf blade on the beginning of September extremely induced leaf senescence in Ginkgo biloba; three weeks after the treatment the leaves disappeared chlorophylls and became yellow, while the control leaves remained still green. Contrarily JA-Me applied to the adaxial side of leaves affected little to induce senescence. When JA-Me was treated on the abaxial side of a half of leaf blade across to the vein, the yellowing widely took place both in acropetal and basipetal directions along vein, but no yellowing was visible in the non-treated half. On the other hand, when JA-Me was applied to the abaxial side of a half of leaf blade along to the vein, yellowing was observed only in both sides of a small area along to the applied area, and little yellowing was visible in the neighboring lateral tissues. JA-Me treatment on the abaxial side of leaf blade greatly increased the levels of JA-Me and jasmonic acid in leaf blade and petiole. Endogenous abscisic acid levels substantially increased during natural and JA-Me-induced leaf senescence, but 1-aminocyclopropane carboxylic acid levels did not change. The contents of cytokinins, gibberellins and auxins identified changed little during natural and JA-Me-induced leaf senescence. These suggest that a cooperative crosstalk between JAs and various hormonal signals, especially abscisic acid, occurs in regulation of G. biloba leaf senescence. Possible different action of JA-Me applied to the abaxial and the adaxial sides of the leaves on leaf senescence is discussed.

The Effect of Suction Side Tubercles on Torque Output of a Steam Turbine Low-Pressure Last Stage Blade

Flow separation and different kinds of stall flows occur under low load conditions for steam turbine last stage blades. In order to delay the flow separation and increase turbine power production, we applied suction side tubercles on steam turbine low-pressure last stage blades in the present study. The amplitude, wavelength, position, and thickness were considered as our design variables. We used the orthogonal test method (OTM) to generate modified blades with different tubercle variables that were then numerically simulated by a three-dimensional computational fluid dynamics (CFD) analysis. The blade axial torque of the nine modified tests was compared with the original blade. The results showed that the application of bionic tubercles on the suction side of the steam turbine blade is a promising solution to improve the blade axial torque for all modified tests with a maximum increase of 33.32% due to the turbulent vortices generated by bionic tubercles.

Inducer/Exducer Matching Characteristics inside Tandem Impellers of a Highly Loaded Centrifugal Compressor

A centrifugal compressor usually operates with low isentropic efficiency and a terrible stable operating range, resulting from the complex impeller flow structure companied with the intense interaction among the impeller and the diffuser downstream. In many studies, the potential of centrifugal compressor tandem-impeller configurations for improving the compressor has been demonstrated. Whereas, compared with the convincing results on the tandem-designed axial compressors, the results on tandem impellers are limited and contradictory. Very little insight has been provided into the flow mechanisms inside tandem impellers, which is considered to be the primary reason for the confusion in tandem impeller design and application. Tandem impellers are expected to exhibit a totally different behavior due to the intense aerodynamic interaction between the inducer and the exducer, which substantially contributes to the flow structure and the compressor performance change. In the present study, a numerical study of a highly-loaded centrifugal compressor with various tandem designs was conducted to explore the inducer/exducer matching characteristics and the underlying flow mechanism inside tandem impellers. Two tandem impeller design parameters, namely, the inducer/exducer clocking fraction and the axial gap (overlap), were considered in the tandem impeller design process. The tandem impeller was also compared to the existing conventional impeller which the tandem impeller was redesigned for. The results demonstrated that the tandem-designed impeller can improve the centrifugal compressor stage performance and intense inducer/exducer interaction can be observed with changes in the clocking fraction and the axial gap (overlap). The tandem impeller performance is sensitive to changes in axial gap (overlap) when the suction side of the exducer blade is circumferentially close to the inducer blade. The fundamental reason for the performance variation in the inducer and the exducer lies in the inducer pressure change in the blade trailing edge that is determined by the Kutta condition. Additionally, the correlation between the tandem impeller slip effect and the discharge flow quality should be emphasized in the inducer/exducer gap jet analysis, in which the jet injection angle and the Coanda effect of the exducer suction surface critically affect the discharge flow characteristics.

Effect of Turbine Blade Tip Cooling Configuration on Tip Leakage Flow and Heat Transfer

Abstract The pressure difference between suction and pressure sides of a turbine blade leads to tip leakage flow, which adversely affects the first-stage high-pressure (HP) turbine blade tip aerodynamics. In modern gas turbines, HP turbine blade tips are exposed to extreme thermal conditions requiring cooling. If the coolant jet directed into the blade tip gap cannot counter the leakage flow, it will simply add up to the pressure losses due to leakage. Therefore, the compromise between the aerodynamic loss and the gain in tip-cooling effectiveness must be optimized. In this paper, the effect of tip-cooling configuration on the turbine blade tip is investigated numerically from both aerodynamics and thermal aspects to determine the optimum configuration. Computations are performed using the tip cross section of GE-E3 HP turbine first-stage blade for squealer and flat tips, where the number, location, and diameter of holes are varied. The study presents a discussion on the overall loss coefficient, total pressure loss across the tip clearance, and variation in heat transfer on the blade tip. Increasing the coolant mass flow rate using more holes or by increasing the hole diameter results in a decrease in the area-averaged Nusselt number on the tip floor. Both aerodynamic and thermal response of squealer tips to the implementation of cooling holes is superior to their flat counterparts. Among the studied configurations, the squealer tip with a larger number of cooling holes located toward the pressure side is highlighted to have the best cooling performance.

Simulation study of Savonius tandem blade wind turbine using an adjustable deflector

The conventional Savonius wind turbine has two inverted cylindrical blades, it can indeed receive fluid impulses from all horizontal directions and produce a greater drag force than other wind turbines. The weakness of Savonius is the resistance in one blade side. Efforts to improve that has been done is to add a blade that serves to increase the local velocity of fluid flow to resist the resistance which is termed Savonius tandem blade (STB). This research was conducted to further reduce the resistance value of one side STB with the addition of an adjustable deflector. The purpose of this study is to obtain information on changes in the torque of the STB wind turbine on variations in the deflector angle and stream velocity. The research method used is numerical simulation using CFD software. A two-dimensional view of the rotor model using deflector was considered. The deflector angle varies start from 15 degrees with an increase also every 15 degrees until the torque decreased. The CFD simulation show there is a significant increase in torque with the addition of a deflector. Maximum torque is not achieved at one deflector angle value but is also influenced by stream velocity. At higher stream velocity there is a tendency to reach the maximum torque required larger deflector angle. Then at a certain point, the torque will decrease when the deflector angle is enlarged.