Blade Trailing Edge Research Articles

A Review of Cooling Studies on Gas Turbine Rotor Blades with Rotation

Increases in power density and thermal efficiency of a highly efficient gas turbine engine motivate an ever-mounting turbine entry temperature. The combined metallurgical and cooling advancements ensure the structural integrity of a gas turbine rotor blade that spins at high rotor speeds in a gas stream with temperatures above the melting point of the blade material. The cooling performances promoted by a variety of heat transfer enhancement methods typical of the coolant channels of the leading edge, the mid-chord region, and the trailing edge of a gas turbine rotor blade are reviewed. The manifested rotational effects on the aerothermal performances of impinging jets and swirl chambers for leading-edge cooling, multi-pass ribbed, dimpled, and/or wavy channels over the mid-chord region, as well as pin fin and latticework narrow ducts in the trailing edge of a gas turbine rotor blade, are summarized and cross-examined. Research orientations for future cooling studies aimed at preventing the development of hot spots in a gas turbine rotor blade are recommended.

Effects of Blade Suction Side Modification on Internal Flow Characteristics and Hydraulic Performance in a PIV Experimental Centrifugal Pump

In this paper, the effects of blade trailing edge (TE) profile modification of the suction side on the internal flow and hydraulic performance in a low-specific speed centrifugal pump are investigated through particle image velocimetry (PIV) analysis. Three impellers with different blade trailing edge profiles named original trailing edge (OTE), arc trailing edge 1 (ATE1), and arc trailing edge 2 (ATE2) are designed for PIV experiments. Results show that blade trailing edge modification of the suction side can significantly change the flow pattern, affecting the hydraulic performance of the model pumps. There is a definite counterclockwise backflow vortex near the suction side of OTE at deep-low flow rate, resulting in a decrease in the uniformity of the flow field at the outlet and the hydraulic performance. ATE1 with a reasonable larger blade outlet angle has the best flow field, and the head and efficiency are increased by about 1.2% and 8%, respectively under the same working condition. The hydraulic performance of ATE2 with the blade outlet angle of 59° is better than that of OTE under low flow rate, but it is less than that of OTE under high flow rate due to the streamline deviation generated on the pressure side. Meanwhile, the energy conversion abilities of the modified model pumps are evaluated by slip factor and the deviation degree of the nominalized local Euler head distribution (NLEHD). Since there is no definite counterclockwise backflow vortex at the outlet after modification, the slip factor of ATEs increases and the energy conversion ability is enhanced. Moreover, the jet-wake phenomenon of ATEs is weakened, and the local Euler head (LEH) increases near the outlet, decreasing the deviation degree of the NLEHD to obtain better energy conversion ability.

Vortex-Pressure Fluctuation Interaction in the Outlet Duct of Centrifugal Pump as Turbines (PATs)

The outlet duct is the only outlet flow component of the pump as turbines (PATs). The flow state within it not only affects its operation stability but also influences the safe operation of downstream process equipment. The undesirable flow phenomenon of the vortex is the main reason for pressure pulsations and vibrations; therefore, it is important to adopt simulation and experimental methods to reveal the vortex-pressure fluctuation interaction characteristics in the outlet duct of PATs. Firstly, the spatial and temporal evolution of the vortex in the outlet duct under different operation conditions were compared based on the Q-vortex identification criterion. Subsequently, the frequency components corresponding to local high amplitude vorticity and pressure pulsations were clarified. Finally, the relationship between vortex evolution and the pressure pulsations in the outlet duct was established. The results showed that the flow rates of the turbine significantly affected the spatial and temporal evolution of the vortex rope in the outlet duct. The front chamber leakage flow and vortex shedding from the blade trailing edge also influenced the vortex distribution characteristics in the outlet duct. The dominant frequency of the pressure pulsation in the outlet duct was 6 fn under different operating conditions, and the amplitude of the pressure pulsation increased with the flow rates. The effect of vortex evolution on the local pressure pulsation characteristics decreased with increasing flow rates. The results can be used to improve and stabilize the operation and further optimization of PATs.

Multi-Conditional Optimization of a High-Specific-Speed Axial Flow Pump Impeller Based on Machine Learning

In order to widen the range of high-efficiency area of a high-specific-speed axial flow pump and to improve the operating efficiency under non-design conditions, the parameters of the axial flow pump blades were optimized. An optimization system based on computational fluid dynamics (CFD), optimized Latin hypercube sampling (OLHS), machine learning (ML), and multi-island genetic algorithm (MIGA) was established. The prediction effects of three machine learning models based on Bayesian optimization, support vector machine regression (SVR), Gaussian process regression (GPR), and fully connected neural network (FNN) on the performance of the axial flow pump were compared. The results show that the GPR model has the highest prediction accuracy for the impeller head and weighted efficiency. Compared to the original impeller, the optimized impeller is forward skewed and backward swept, and the weighted efficiency of the impeller increases by 1.31 percentage points. The efficiency of the pump section at 0.8Qd, 1.0Qd, and 1.2Qd increases by about 1.1, 1.4, and 1.6 percentage points, respectively, which meets the optimization requirements. After optimization, the internal flow field of the impeller is more stable; the entropy production in the impeller reduces; the spanwise distribution of the total pressure coefficient and the axial velocity coefficient at the impeller outlet are more uniform; and the flow separation near the hub at the blade trailing edge is restrained. This research can provide a reference for the efficient operation of pumping stations and the optimal design of axial flow pumps under multiple working conditions.

Interaction mechanism between the tip leakage flow and inlet boundary layer in a highly loaded compressor cascade based on scale-adaptive simulation

Based on the scale-adaptive simulation, the interaction mechanism between the tip leakage flow (TLF) and the inlet boundary layer (IBL) and its effects on the tip flow field and aerodynamic performance of the compressor cascade were investigated. The time-averaged results show that the IBL reduces the blade tip load near the leading edge region, decreases the axial momentum of the TLF, and inhibits the development of the TLF to a certain extent. On the other hand, the IBL promotes the coupling of the tip leakage vortex, secondary vortex, and separation vortex and induces breakdown, resulting in a large area of severe flow separation in the corner region, greatly reducing the diffusion capacity and significantly increasing the flow loss in the tip region. The analysis of the unsteady transient flow fields indicates that the unsteady fluctuation in the tip region is mainly caused by the tip leakage vortex and flow separation near the blade trailing edge. The former is suppressed under the influence of the IBL, while the latter is amplified. The high-intensity oscillation due to the breakdown and decomposition of the tip vortex structures plays a critical role in the fluctuation of the cascade performance. By means of proper orthogonal decomposition, it is found that the IBL enhances the fluctuation of small-scale vortex structures related to flow separation and leakage flow and makes the stability of the tip flow field worse.

Dynamic modeling of rotary blade crack with regard to three-dimensional tip clearance

To investigate the dynamic characteristics of the three-dimensional blade tip clearance (3D-BTC) of rotary blade cracks, a novel dynamic model of the rotary blade crack with regard to the 3D-BTC is derived based on the Timoshenko beam theory. In this model, the modal shape functions of the blade are derived based on the transfer matrix method, and the axial and circumferential aerodynamic loads are introduced to better obtain the dynamic responses of the blade vibration. Then, a breathing crack model of the blade trailing edge crack is established by considering the coupling effects of the centrifugal stress, axial bending stress, and circumferential bending stress. The crack opening width is introduced into the breathing crack model to comprehensively depict the crack together with the crack depth and crack location. Moreover, a numerical calculation method for the 3D-BTC is proposed for the rotary blade with cracks. The dynamic model is validated by comparing it with the finite element model and the experiment. Finally, the effects of the blade trailing edge crack on the 3D-BTC are analyzed. The results show that the cracked blade's first-order natural frequency decreases with the crack depth increase, and it increases first and then decreases slightly when the crack location moves away from the blade root. The effects of crack opening width on the first-order natural frequency are relatively small due to its small size. In the meantime, the nonlinear damage indicators (NDIs) of the 3D-BTC are calculated. The results show that the NDIs can reflect the severity of the blade crack, and the proposed model can comprehensively analyze the effects of rotary blade crack on the 3D-BTC, which is beneficial for the diagnosis method for blade cracks based on the 3D-BTC.

Study on Influential Mechanism of Trailing Edge Sweep Angle on Aerodynamic Noise of a Centrifugal Air Compressor

As the main noise source in the hydrogen fuel cell system, the noise level of the centrifugal air compressor greatly affects the comfort of the hydrogen fuel cell vehicle, and can be effectively reduced by optimizing the trailing edge sweep angle of the blade. In this paper, the computational fluid dynamics model was used to study the influence of the trailing edge sweep angle on the aerodynamic performance and flow characteristics of a centrifugal air compressor for vehicle fuel cells. The Ffowcs Williams–Hawkings equation and the computational fluid dynamics–boundary element coupling method were adopted to calculate the dipole source strength on the surface of the blade and the radiated aerodynamic noise, respectively, under the different trailing edge sweep angles. The results showed that the trailing edge sweep could lead to an increase in pressure ratio as well as isentropic efficiency, and a decrease in the intensity of flow separation. Meanwhile, the sound pressure level of the compressor under each working condition could be effectively reduced by the trailing edge sweep. When the rotation speed was 80,000 r·min−1 and the blade trailing edge sweep angle was 15°, the sound pressure level of the radiated aerodynamic noise was 5.8 dBA lower than that without sweep.

Surface film cooling characteristics of rectangular holes along the trailing edge of a transonic turbine blade tip

The present study investigates film cooling in the trailing edge region of a transonic turbine blade tip, with an arrangement which is significantly different from all previous blade tip investigations. In particular, five rectangular film cooling holes, located along the tip near the blade trailing edge and positioned downstream of a squealer recess region, are employed. Each film cooling hole is oriented at a 45° angle relative to the blade tip surface. Heat transfer coefficient ratio data, and adiabatic film cooling effectiveness data are provided for two tip gaps over a range of blowing ratios. Tip gap magnitudes are 1.4 mm and 0.8 mm, which correspond to 1.16% and 0.66% of the true blade span, respectively. Surface heat transfer characteristics are measured using a transient impulse-response approach with infrared thermography. Along most of the trailing edge tip surface, adiabatic film cooling effectiveness values are locally augmented for all blowing ratios BR and for both tip gaps considered, which evidences substantial film coolant concentrations near the blade tip surface. Local values of adiabatic film cooling effectiveness often increase with increasing blowing ratio and are consistently higher for the smaller tip gap. In general, only minor differences between the 0.8 mm and 1.4 mm tip gap heat transfer coefficient ratio data sets are present, with marginally higher values of heat transfer coefficient ratios for the smaller tip gap. Together, heat transfer coefficient ratio and adiabatic film cooling effectiveness data suggest that the thermal protection offered by the 0.8 mm tip gap along the trailing edge tip region is superior to that of the 1.4 mm tip gap for a range of blowing ratios.

Investigation of the relationship between the 3D flow structure and surface heat transfer within a realistic gas turbine blade trailing edge internal serpentine cooling channel

Proper internal cooling of the thin trailing edge of gas turbine blades is crucial for blade lifespan extension. In this study, numerical and experimental analyses are conducted to elucidate the relationship between the 3D flow structure and surface heat transfer in a realistic three-pass serpentine channel within the trailing edge of a blade. Magnetic resonance velocimetry is conducted to first experimentally validate the mean velocity field from the Reynolds-averaged Navier Stokes simulation. Heat transfer and friction coefficients are then obtained through numerical analysis. The serpentine channel is investigated at each section. The inlet S-duct contributes to heat-transfer promotion upstream of the first ribbed passage due to an intense vortex pair. This vortex pair generates high streamwise velocity along the pressure and suction side, as well as additional friction due to secondary flow. In the second passage, film cooling holes make the separation bubble attach only to the suction side and create a high streamwise velocity region around the holes by bringing the surrounding flow to the periphery of the holes. This effect also occurs near the ejection holes in the third passage. These flow features within the passages are analyzed using the momentum distortion parameter (D) and secondary flow energy parameter (E). We found that the distortion parameter is not sufficient in predicting the heat transfer trend due to in-plane wall shear. Thus, the estimator is revised as (D+E)/2 to additionally account for secondary flow. This composite parameter shows good performance in estimating heat transfer for all the passages, compared to the friction coefficient which is hard to directly measure.

Experimental study of the flow of the Tr-Francis turbine along the no-load curve

Emergence of new renewable energies, such as solar or wind power, has introduced intermittency on the grid. Hydraulic turbines, initially designed to perform close to their best efficiency point, are more and more at off-design operating conditions, such as no-load regimes, when the runner rotates without energy extraction. These no-load regimes are characterized by complex flow phenomena inducing fluctuations of the blade loading and resulting in a reduced lifetime of the runner. Understanding the origins of pressure fluctuations in no-load conditions is consequently essential to prevent fatigue damage to the turbine. This paper presents the study, with experimental flow visualization, pressure measurements and numerical simulations, of the flow behavior at speed no-load in a medium head Francis turbine model. Evolution of the different flow structures along the no-load curve is then assessed. At speed-no-load, flow visualizations show the presence of a cavitating zone at the blade trailing edge. According to the results of the numerical simulations, this zone seems to correspond to the region where a backflow in the draft tube enters the runner. This interaction results in a backflow inside the runner and in a blockage of the upper part of the inter-blade channel. Sensitivity of this cavitating region to test parameters (discharge and rotation speed) is investigated for different no-load operating points with high-speed visualization at a constant cavitation number. Decrease of the energy coefficient tends to intensify the phenomena and increase the volume of cavitation.

Numerical Investigations of a Non-Uniform Stator Dihedral Design Strategy for a Boundary Layer Ingestion (BLI) Fan

A distributed propulsion system has the advantage of saving 5–15% fuel burn through ingesting the fuselage boundary layer of an aircraft by fan or compressor. However, due to boundary layer ingestion (BLI), the fan stage will continuously operate under serious inlet distortion. This will lead to a circumferentially non-uniform flow separation distribution on the stator blade suction surface along the annulus, which significantly decreases the fan’s adiabatic efficiency. To solve this problem, a non-uniform stator dihedral design strategy has been developed to explore its potential of improving BLI fan performance. First, the stator full-annulus blade passages were divided into blade dihedral design regions and baseline design regions on the basis of the additional aerodynamic loss distributions caused by BLI inlet distortion. Then, to find the appropriate dihedral design parameters, the full-annulus BLI fan was discretized into several portions according to the rotor blade number and the dihedral design parameter investigations for dihedral depth and dihedral angle were conducted at the portion with the largest inflow distortion through a single-blade-passage computational model. The optimal combinational dihedral design parameter (dihedral depth 0.3, dihedral angle 6 deg) was applied to the blade passages with notable flow loss which were mainly located in the annulus positions from −120 to 60 degrees suffering from inlet distortion, while the blades in the low-loss annulus locations were unchanged. In this way, a non-uniform stator dihedral design scheme was achieved. In the end, the effectiveness of the non-uniform stator dihedral design was validated by analyzing the internal flow fields of the BLI fan. The results show that the stator dihedral design in distorted regions can increase the inlet axial velocity and reduce the aerodynamic load near the blade trailing edge, which are beneficial for suppressing the flow separations and reducing aerodynamic loss. Specifically, compared with the baseline design, the non-uniform stator dihedral design has achieved a reduction of aerodynamic loss of about 7.7%. The fan stage has presented an improvement of adiabatic efficiency of about 0.48% at the redesigned point without sacrificing the total pressure ratio. In the entire operating range, the redesigned fan has also shown a higher adiabatic efficiency than the baseline design with no reduction of the total pressure ratio, which provides a probable guideline for future BLI distortion-tolerant fan design.

Performance analysis of geometrically optimized PaT at turbine mode: A perspective of entropy production evaluation

In the field of hydroelectric power, Pump as Turbine (PaT) is an important tool to achieve recycling the redundant kinetic energy in small stream/rivers. However, due to the contradiction between the reverse fluid flow working at turbine mode and the designed flow passage of pump geometry, the internal hydraulic loss in PaT is excessive. As a result, it renders the PaT performance extremely low affecting its wide applications with the demand of high efficiency operation. Therefore, this paper aims to optimize the geometric parameters of the impeller in PaT turbine mode under three different typical flow conditions (i.e. rated, best efficiency, and overload working conditions). After the geometric optimization, the internal energy losses among the flow passages are analyzed by using the entropy production method. The results show that the impeller passage exhibits obviously higher entropy loss in comparison to the volute and the outlet pipe. Inside the impeller, the blade leading and trailing edges on both suction and pressure sides are the locations where the majority of the impeller energy losses occur, and the high entropy area is concentrated at the impeller inlet area. Moreover, The energy loss gradually decreases from blade leading edge (BLE) to blade trailing edge (BTE), and the entropy production decreases from the blade pressure side (PS) to the blade suction side (SS) due to the large mixing flow loss from PS to SS. It is concluded that the entropy production analysis is effective in explaining the PaT power losses caused by the geometric mismatch of different components including inlet, impeller, and outlet, providing the reference value for the geometric optimization of other turbine machinery.

Experimental Investigation of Fenestron Noise

The noise radiation of an EC135 Fenestron is investigated by means of flight tests. The noise emission was measured with ground microphones during several different maneuvers. These include hover, rearward flight, and forward flight at different combinations of the side slip angle and the airspeed. In hover, a high level of broadband noise is observed. A comparison with available engine noise data suggested that engine noise is not dominant in hover. In rearward flight, the Fenestron may encounter a relatively clean aerodynamic inflow. However, the measurements do not indicate a reduction in noise radiation of the Fenestron. For rearward flight, a significant increase in main rotor noise is observed. Flights at different combinations of the side slip angle and airspeed show that the Fenestron radiates high levels of tonal noise at high-speed flight at negative side slip. The most likely cause for this is a highly disturbed inflow caused by flow separations of the diffusor outlet edge and the sharp trailing edges of the stator blades. Measurements of the tail boom yaw moment and Fenestron drive shaft torque imply that a reverse flow is possible at medium airspeed, while the Fenestron thrust does not reverse sign. Only at higher airspeeds and negative side slip, it is possible to achieve a thrust reversal in addition to a flow reversal.

Wavy Trailing Edge Feasibility for Aircraft Engine Composite Fan Blade

Attempts to add the advanced technologies to aerospace composite structures like fan blade have been on in recent times to further improve its performance. As part of these efforts, it has been proposed that the wavy trailing edge could be used in the blade to reduce the noise level. It has been also proposed that it’s structural feasibility could be studied by fabricating coupons representing blade like boundary conditions and mimicking max strain contours of wavy trailing edge of blade and testing them. Suitable size coupons (baseline flat and ones with wavy edge) were designed, and appropriate boundary condition was suggested for tests. The four-point bend tests were performed on baseline flat and wavy edge coupons and after analyzing the results it was concluded that some wavy edge configurations coupons do show some knock down in the failure load/strain but the optimized wavy edge configuration coupons show almost no knockdown (within scatter) in the failure load/strains. This leads to the conclusion that the wavy edge configuration under consideration has sufficient structural integrity as per the representative coupon test

Study on the solid particle erosion characteristic of top gas pressure recovery turbine under variable working condition

Aiming at the problem of particle erosion in top gas pressure recovery turbines, the physical and chemical properties of the sampled gas dust particles are tested in this paper, and particle motion behavior and erosion characteristics in the turbine cascade are investigated by employing a validated numerical method. On this basis, the influence mechanism of adjustable stator angle and rotate speed on the erosion characteristics of blades under variable working conditions is quantitatively explored. Results show that the erosion damage of the first-stage stator S1 and rotor R1 are mainly initiated by particles with different size. The change of adjustable stator angle will change the load and gas enthalpy drop distribution of the cascade, which then affects the impingement velocity and position of the particles. When adjustable stator angle reduces from 44.2 to 25% opening, erosion of S1 trailing edge grows about 20%, while the erosion of R1 trailing edge reduces by 50%. The change of rotating speed will change the relative magnitude of the particle centrifugal force and airflow drag force, which in turn affects the particle’s trajectory and impingement velocity. When rotate speed increases from 3,000 to 4,500 r/min, both the particle impingement velocity and escape rate increase, resulting in doubling of the erosion on blade leading edge and halving of the erosion on blade trailing edge. Finally, for the high rotation speed TRT operating under variable working conditions, some insightful suggestions are given to minimize the erosion damage of the turbine blades.

Aerodynamic Interaction of Volute With Rotor in a Nozzleless Radial Turbine

Abstract Aerodynamic interaction of rotor with stator is the primary cause of high cycle fatigue of radial turbine blade. However, few studies have been carried out on aerodynamic interaction in nozzleless radial turbines. This paper studies aerodynamic interaction in a nozzleless radial turbine via the experimentally validated numerical method. The results suggest that several flow phenomena are related to blade excitation. First, when the blade sweeps by the volute tongue, the tongue wake induces a strong separation vortex at the blade leading edge and interacts with it. As the tongue wake migrates downstream, it deforms into a triangular shape across the rotor passage. Second, the potential field of the volute leads to drastic fluctuations of blade load as well as tip leakage flow. Importantly, the tongue wake interacts with the tip leakage vortex in the vicinity of blade trailing edge. This phenomenon results in strong disturbance to pressure fluctuations on suction surface at low pressure ratio, and the frequency of disturbance is roughly one order higher than that of potential field. However, its influence can be neglected at high pressure ratio. Furthermore, the details of vortex evolution in the rotor passage are discussed via the time-space contour plots of pressure difference. Various behaviors including propagation speed, direction, and strength can be well manifested by this method. Finally, the strong influence of unsteady interaction on blade excitation in the nozzleless turbine is confirmed by a direct comparison of blade loads in unsteady conditions with that in quasi-steady conditions.

Numerical Investigation on the Effect of Asymmetry of Flow Velocity on the Wake Vortex of Hydrofoils

The Karman vortex street is a common flow phenomenon. In hydraulic machinery, it is usually located downstream of the guide vanes and the runner blades, which reduces hydraulic performance and may also cause fatigue damage to the structure. The latest research suggested that the difference in velocity gradient on each side of the blade trailing edge may have a significant impact on the strength of the wake vortex. The current work aims to verify the above conclusion and further explore the influence of asymmetry of flow velocity on the wake vortex. A numerical model with the velocity ratio, α, between the two sides of the hydrofoil as the only variable was designed, and the wake characteristics were solved by a computational fluid dynamics (CFD) method based on the finite volume. The unsteady Reynolds-average Navier–Stokes (URANS) equations were numerically solved by coupling with a transitional shear-stress transport (SST) turbulence model. The results showed that with the increase of α, the vortex shedding frequency decreased first, and then increased after reaching the critical velocity ratio αc1 ≈ 1.4. The vortex intensity first gradually decreased, and the vortex street suddenly disappeared after reaching the critical velocity ratio αc2 ≈ 2.2. The value of αc1 was affected by the thickness of the trailing edge, and αc2 was affected by the thickness and the Reynolds number. Besides, the asymmetry of the flow velocity also affected the effectiveness of the trailing-edge trimming. This research can provide references for the design of hydraulic machinery and other submerged structures.

An energy consumption improvement method for centrifugal pump based on bionic optimization of blade trailing edge

The centrifugal pump is one of the most widely used types of power machinery in the water resource utilization and chemical industries. Its energy consumption cost accounts for a large proportion of its total economic cost. In this paper, an energy consumption improvement method for centrifugal pump is proposed by referring to the bionic structure to reduce the energy loss of the centrifugal pump. Four types of impellers with different types of sinusoidal tubercle trailing edges (STTE) are designed. Experiment and numerical simulation are combined to explore the beneficial effects of STTEs. Experimental research shows that this structural change will not affect the performance of the pump. On this basis, the entropy generation rate analysis method was introduced, and the numerical calculation results were analyzed to explore the internal influence of the STTE on the energy loss characteristics of the centrifugal pump. Results show that the use of STTEs can adjust the proportion of energy loss of each component in a centrifugal pump and effectively reduce the overall energy loss. Quantitative research indicated that the STTE3 has the optimal effect of reducing energy consumption. The use of STTE3 can reduce the total energy consumption by more than 5% at all flow rate conditions and reach a peak of 16.95% under 1.2 times nominal flow rate conditions. Thus, the bionic structure optimization method to improve the internal energy loss characteristics of centrifugal pumps will be beneficial and can provide a certain degree of reference for the hydraulic design of centrifugal pumps.

Performance Prediction and Geometry Optimization for Application of Pump as Turbine: A Review

Pump as Turbine (PAT) is a technically and economically effective technology to utilize small/mini/micro/pico hydropower, especially in rural areas. There are two main subjects that influence the selection and application of PAT. On the one hand, manufacturers of pumps will not provide their characteristics under the turbine mode, which requires performance prediction methods. On the other hand, PAT efficiency is always slightly lower than that of pump, which requires further geometry optimization. This literature review summarized published research studies related to performance prediction and geometry optimization, aimed at guiding for selection and optimization of PAT. Currently, there exist four categories of performance prediction methods, namely, using BEP (Best Efficiency Point), using specific speed, loss modeling, and polynomial fitting. The using BEP and loss modeling methods are based on theoretical analysis, while using specific speed and polynomial fitting methods require statistical fitting. The prediction errors of published methods are within ±10% mostly. For geometry optimization, investigations mainly focus on impeller diameter and blade geometry. The influence of impeller trimming, blade rounding, blade wrap angle, blade profile, blade number, blade trailing edge position, and guide vane number has been studied. Among published methods, the blade rounding and forward-curved impellers are the most effective and feasible techniques.

Initiation Mechanism of Transverse Cracks in Wind Turbine Blade Trailing Edge

Transverse crack often occurs in the trailing edge region of the blade when subjected to the excessive edgewise fatigue load. In this paper a refined model was established through local mesh refinement methods in order to investigate the initiation mechanism of crack and its extension in blade trailing edge. The material stress around the crack in trailing edge region under different thicknesses is calculated based on the fracture mechanics theory. The factors affecting the fatigue robustness of blade trailing edge are concluded by investigating the results of finite element analysis and coupons test. Compared with the laminate, the lower fatigue strength of the adhesive is the cause of the transverse crack of the adhesive joint at the trailing edge. The increase of the adhesive thickness at the adhesive joint will significantly increase the stress concentration factor at the crack region and accelerate the crack extension of the laminate. In final, a practical design scheme to prevent crack initiation is given for the manufacture of the wind turbine blade.