Blade Forces Research Articles

Study on hydraulic characteristics and internal flow mechanism of composite blade disc pump

Abstract Disc pump is widely used in difficult-pump-medium transportation such as petroleum and chemical industry. Discontinuous blade impellers play an important role in the passability and energy efficiency of disk pump. The research of design and internal flow mechanism are particularly important. Based on the structural characteristics and the internal flow mechanism of the original model, the improved design of the blade structure is carried out. Through the experimental verification and the numerical analysis of multiple working conditions, the influence law of the new composite blade on the hydraulic characteristics and internal flow mechanism of the disc pump is obtained. The results show that the error of energy efficiency characteristics of simulation and experiment under different flow conditions is within 5%, and the accuracy of simulation results meets the requirements; The hydraulic characteristics of the improved model are about 5.8% higher than that of the original model. The driving force of the new composite blade is more sufficient and the flow field is improved more obviously; The low pressure is located in the center of the impeller and gradually increases to the outlet of the impeller. There is obvious energy and mass conversion between the bladed region and bladeless region. The research results can provide a reference for the structural design of disc pump composite blade and the analysis of internal flow mechanism.

Study of aerodynamic parameters of the sail blade

This article studies the aerodynamic characteristics of a triangular sail blade of various parameters. For this purpose, we made a triangular sail blade with a dynamically changing surface shape. The airflow velocity varied from 3 to 12 m/s. The dependences of the aerodynamic forces of the sail blade on the flow velocity were investigated at various angles of the apex of the triangular blade. The experiments were carried out at different vertices of the angles: 00; 300; 600; 900. As a result of the experiment, it was revealed that at the vertex angle γ = 900, the triangular sail blade has optimal aerodynamic parameters. The dependences of the aerodynamic coefficients on the dimensionless angle of attack are obtained. It is found that the optimal number oftriangular blades for a wind power plant with sailing blades is 6. It is established that at the angle of attack α= 00, the maximum value of the middle section of the wind wheel to the streamlined airflow will introduce a decrease in the value of the drag coefficient with an increase in attack α. The analysis of the experiment results on the change in α from the speed of the airflow of the sail blade is carried out. When the blade position changes, drag changes relatively to the airflow. The wind wheel will change its position relative to the stream with an increase in the attack angle. With an angular position change, the area of the middle section of the wind wheel begins to decrease relative to the incoming flow. With a decrease in the middle section of the wind wheel, the drag force decreases, and the drag coefficient decreases accordingly. Thus, the total result of pressure changes on the leeward and windward surfaces of the sail can be represented as one resultant aerodynamic force directed at an angle to the line perpendicular to the wind direction.

Comparison of Three-Dimensional Numerical Methods for Modeling of Strut Effect on the Performance of a Vertical Axis Wind Turbine

This paper compares three different numerical models to evaluate their accuracy for predicting the performance of an H-rotor vertical-axis wind turbine (VAWT) considering the influence of struts. The strut of VAWTs is one factor that makes the flow feature around the turbine more complex and thus influences the rotor performance. The focus of this study is placed on analyzing how accurately three different numerical approaches are able to reproduce the force distribution and the resulting power, taking the strut effect into account. For the 12 kW straight-bladed VAWT, the blade force is simulated at three tip speed ratios by the full computational fluid dynamics (CFD) model based on the Reynolds-averaged Navier–Stokes (RANS) equations, the actuator line model (ALM), and the vortex model. The results show that all the models do not indicate a significant influence of the struts in the total force over one revolution at low tip speed ratio. However, at middle and high tip speed ratio, the RANS model reproduces the significant decrease of the total tangential force that is caused due to the strut. Additionally, the RANS and vortex models present a clear influence of the struts in the force distribution along the blade at all three tip speed ratios investigated. The prediction by the ALM does not show such distinctive features of the strut impact. The RANS model is superior to the other two models for predicting the power coefficient considering the strut effect, especially at high tip speed ratio.

Effect of the odd and even number of blades on the hydrodynamic performance of a pre-swirl pumpjet propulsor

A numerical study based on detached eddy simulations is conducted to investigate the effects of the odd and even number of rotor/stator blades, that is, nr/ns, on the hydrodynamic performance of a pre-swirl pumpjet propulsor (PJP). In this paper, six PJPs, the PJP 6-4 (ns–nr), 8-6, 10-8, 7-5, 9-7, and 11-9, are created. The hydrodynamic performance, the unsteady force of blades, and the wake structure of the PJPs are compared. The results show that the frequency of the fluctuating force of the whole rotor highly depends on the number or, more specifically, the parity of nr. When the parameter nr is the even number, it can be found that the total unsteady force of the rotor blades will be strengthened at the k-order stator-blades-passing frequency (k=1/2nr). Moreover, it indicates that the superposition-enhancement coefficient (is defined as A*) at k=1/2nr equals to nr, at least from the present tests. In terms of both the rotor and stator numbers are even, a phenomenon of the rotor–stator resonance occurs at f=1/2nsnrfn, where fn represents the hub rotational frequency. This work is expected to give some insight in the design of a PJP.

Draught force prediction from soil relative density and relative water content for a non-winged chisel blade using finite element modelling

This study aims to develop a model for prediction of the draught force of a new narrow non-winged chisel blade as a function of tillage depth (d), forward speed (v), soil relative water content (wrel), and soil relative density (ρrel) based on combination of statistical and finite element (FE) models. The soil-chisel blade interaction was simulated for various combinations of relative density and relative water content of a sandy loam soil at three levels of forward speed (i.e., 2, 3, and 5 km h−1) and three levels of tillage depths (i.e., 0.15, 0.2, and 0.25 m) using finite element method. The draught force of each simulation was obtained and used to develop a statistical model. A simple model with an adjusted coefficient of determination (Radj2) of 0.81 and the root mean square error (RMSE) of 0.3 kN was proposed for draught force. This model was tested for a set of experimental data obtained in a clay loam soil. The fitted regression line to the data showed that the predicted draught forces lie within bounds of ±6% of the measured values with a coefficient of determination of 0.96. In general, the results of this study showed that using relative density and relative water content, a prediction model could be developed for draught force to work across soil textures. Further studies in a wider range of soil textures are suggested to evaluate the model for the tillage tool.

A numerical study of strut and tower influence on the performance of vertical axis wind turbines using computational fluid dynamics simulation

AbstractThis paper presents the influence of the strut and the tower on the aerodynamic force of the blade for the vertical axis wind turbine (VAWT). It has been known that struts degrade the performance of VAWTs due to the inherent drag losses. In this study, three‐dimensional Reynolds‐averaged Navier–Stokes simulations have been conducted to investigate the effect of the strut and the tower on the flow pattern around the rotor region, the blade force distribution, and the rotor performance. A comparison has been made for three different cases where only the blade; both the blade and the strut; and all of the blade, the strut, and the tower are considered. A 12‐kW three‐bladed H‐rotor VAWT has been studied for tip speed ratio of 4.16. This ratio is relatively high for this turbine, so the influence of the strut is expected to be crucial. The numerical model has been validated first for a single pitching blade and full VAWTs. The simulations show distinguished differences in the force distribution along the blade between two cases with and without struts. Since the wake from the struts interacts with the blades, the tangential force is reduced especially in the downwind side when the struts are considered. The calculated power coefficient is decreased by 43 %, which shows the importance of modeling the strut effect properly for accurate prediction of the turbine performance. The simulations also indicate that including the tower does not yield significant difference in the force distribution and the rotor power.

INVESTIGATION OF THE AERODYNAMIC FORCES OF A TRIANGULAR WIND TURBINE BLADE FOR THE LOW WIND SPEEDS

This article investigates the aerodynamic characteristics and finds the critical angle of attack of a triangular sail blade of a wind turbine for low wind speeds. For this purpose, a triangular sail blade of various parameters has been developed. The prototype is made of metal frame rods, the material of the triangular sail blade consists of a light and durable material (silk), one end of which is fixed to the top of the frame with a strong thread and support rods and bearing with an inner diameter of 8 mm. A sail blade differs from other blades in that the sails are made with the ability to change the angle of attack using a movable thread. To determine the critical angle of attack, the aerodynamic forces of the sail blade were investigated at different angles of attack 00 ; 150 ; 300 ; 450 , 600 ; 750 ; 900 . From the data analysis, it was found that the critical angle of attack is 150 , at which the value of the lift is maximum. Furthermore, at the critical angle of attack, the dependences of the lift and drag force on the air flow velocity were established, the value of which varied from 4 to 12 m/s.

Methodology for Evaluating the Cutting Force of Planar Technical Blades Used in Flatfish Processing

In the food industry, there are many varieties of technical blades with different contours as well as different cutting edge geometries. The evaluation of the ability of technical blades to separate (cut) animal tissues is not a simple task and is usually based on the evaluation of the cutting effects in a technological process. This paper presents a methodology for evaluating the cutting force of technical blades used in food processing. A specially made test stand with numerical control was used in the study. Its application enabled a comparison of cutting force values for four different cutting edge geometries of planar knives used in the skinning operation of flat fishes. A unique feature of the conducted research was the use of a relatively high cutting speed value of vf = 214 mm/s, which corresponded to the real conditions of this process carried out in the industry. Obtained test results allow unambiguously choosing the most advantageous variant of knife geometry from among four different variants used for the tests. The results showed a clear relationship between the cutting force value and the value of the tip angle of the blades tested: for blades with the lowest tip angle, the lowest cutting force values were obtained.

Reducing underwater radiated noise of a SUBOFF model propelled by a pump-jet without tip clearance: Numerical simulation

A pump-jet without tip clearance is proposed to propel a scaled SUBOFF model. The hydrodynamic performance of the pump-jet behind the SUBOFF, modal characteristics and vibro-acoustic responses of the SUBOFF – pump-jet under unsteady excitations are reported and compared with those by the pump-jet with a 2 mm tip clearance. The hydrodynamics are obtained by CFD (Computational Fluid Dynamics) and vibro-acoustic responses are predicted by coupled FEM (Finite Element Method) and direct BEM (Boundary Element Method). The CFD model of the pump-jet without tip clearance is validated by experimental results in a cavitation tunnel through steady hydrodynamics. Fluctuation pressure, standard deviation of fluctuation pressure and spectra of the new pump-jet behind SUBOFF are demonstrated. It is shown that fluctuation pressure on a single blade and fluctuation force of the rotor are suppressed remarkably, as well the amplitudes at BPF (blade passing frequency) and its multiples is greatly attenuated for the monitoring points on the rotor and duct. Since a shroud is added for rotor blades and stiffness is presented between the shroud and the duct due to hydrodynamic lubrication, a new mode of coupled rotor and duct deformation is borne and modal frequency at longitudinal mode of shaft is increased due to change of the cantilever supporing state of rotor blades. New force transmission paths for the rotor via the duct to excite the hull, and that for the duct via the shafting to excite the hull are presented, which will transmit part of vibration energy when applying excitation forces on the rotor or duct. The sound radiation power level is greatly suppressed after eliminating the tip clearance. Especially at the characteristic structural modes due to combined effect of alternating the structural modes to be far away from the characteristic frequencies of excitation forces and suppressing fluctuation pressures on the rotor and duct.

Estimation of blade forces in wind turbines using blade root strain measurements with OpenFAST verification

This paper introduces an inference method for computing the forces and bending moments on operating wind turbine blades using strain measurements and supervisory control and data acquisition (SCADA) data. Operational data from four months of a Clipper Liberty C96 2.5 MW turbine instrumented with interferometric strain sensors at the blade roots as well as SCADA data such as wind speed, rotor hub speed, and blade pitch angle allow for accurate calculation of blade forces and moments. To perform such calculations, certain structural properties of the turbine blades must be inferred in the absence of detailed, proprietary information. This is done by inferring missing information from the National Renewable Energy Laboratory (NREL) 3 MW WindPACT reference wind turbine specifications. The derived forces and moments computed on the blades of the Clipper turbine are compared with the behavior of the NREL 3 MW reference turbine according to OpenFAST simulation outputs. Comparison of blade root reaction forces to OpenFAST outputs match closely, demonstrating that this inference method can be used to successfully estimate the internal forces and bending moments acting on the blades. These methods are useful on turbines for which all the structural information is not available.

Open water performance of B-Series marine propellers in tandem configurations

The hydrodynamic performance of 4-bladed B-series tandem propellers with different design configurations in open water is numerically investigated using a RANS-based CFD solver. The integration of the co-rotating aft propeller increases the resultant thrust and torque coefficients in the entire range of propeller loading. The open water efficiency at moderate to high propeller loadings is reduced, but the range of positive thrust output is increased.Due to the induced velocities and flow acceleration caused by the forward propeller, a higher pitch ratio should be adopted for the aft propeller to generate the blade forces. While the forward propeller behaves very similar to a conventional single propeller, the thrust and torque coefficients of the aft propeller show minimal variations with advance coefficient due to high induced velocities. At higher advance coefficients and blade sections closer to the hub there is greater deviation of forces generated by the aft propeller blade as compared to a single propeller of similar design. Parametric investigations are presented, highlighting the influence of axial spacing, relative angular position, pitch difference, and diameter ratio between the forward and aft propellers on the open water performance. From the present study, a pitch ratio difference of 0.3 may be maintained between the two propellers for optimal open water performance.

A throughflow-based optimization method for multi-stage axial compressor

A multi-objective optimization tool for multi-stage axial compressors is developed based on an automatically calibrated throughflow method. The Euler-based throughflow equations with blade force terms are solved using a time-marching finite volume method to obtain the meridional flow fields, while the traditional empirical deviation and loss correlation are substituted by several Kriging metal models constructed based on the circumferentially averaged results of three-dimensional computational fluid dynamics simulations. Optimization maximizing both the total pressure ratio and adiabatic efficiency is performed to search for the optimal flowpath and radial distributions of geometrical parameters by using the non-dominated sorted genetic algorithm II method. A low-speed 4.5-stage axial compressor is chosen as the test case to verify the procedures, including throughflow solver validation, design optimization, etc. The throughflow solver has proved to be reliable. The optimization under the design operation condition achieves a great increase in the total pressure ratio and a small increase in adiabatic efficiency. Moreover, improvements in the total pressure ratio and stall margin are also observed for the optimal configuration in this optimization, with a decrease in the cost of adiabatic efficiency under the operation condition near stall.

Investigating of Flow Field and Power Performance on a Straight-blade Vertical Axis Wind Turbine with CFD Simulation

Forecasting the power performance and flow field of straight-blade vertical axis wind turbine (VAWT) and paying attention to the dynamic stall can enhance more adaptability to high turbulence and complicated wind conditions in cities environment. According to the blade element-momentum theory, the force of blade is analyzed in one period of revolution based on the structural characteristics of straight blade airfoil. The power performance of VAWT obtained by computational fluid dynamics (CFD) simulation is compared with experiment to estimate the accuracy about the numerical simulation results. As a result, the trend of average value of simulation Cpower is entirely consistent with the value of experiment data, and the extreme value of average Cpower of VAWT is 0.225 for tip speed ration (TSR) λ=2.19 when the freestream velocity is 8 m/s. The flow separation around the blade surface also gradually changes with the azimuth angle increasing, and the maximum pressure difference on the blade surface appears in the upstream. In the case of high leaf tip velocity, the synthetic velocity is much larger than the incoming wind velocity, and the angle of synthetic velocity increases slightly with the increase of blade tangential velocity. Thus, the angles of attack are very close in two TSRs λ=2.19 and 2.58. The research provides a computational model and theoretical basis for predicting wind turbine flow field to improve wind turbine power performance.

Spectral proper orthogonal decomposition of compressor tip leakage flow

To identify the spatiotemporal coherent structure of compressor tip leakage flow, spectral proper orthogonal decomposition (SPOD) is performed on the near-tip flow field and the blade surface pressure of a low-speed compressor rotor. The data used for the SPOD analysis are obtained by delayed-detached eddy simulation, which is validated against the experimental data. The investigated rotor near-tip flow field is governed by two tip leakage vortices (TLV), and the near-tip compressor passage can be divided into four zones: the formation of main TLV (Zone I), the main TLV breakdown (Zone II), the formation of tip blockage cell (Zone III), and the formation of secondary TLV (Zone IV). Modal analysis from SPOD shows that a major part of total disturbance energy comes from the main TLV oscillating mode in Zone I and the main TLV vortex shedding mode in Zone III, both of which are low-frequency and low-rank; on the contrary, modal components in Zones II and IV are broadband and non-low-rank. Unsteady blade forces are mainly generated by the impingement of the main TLV on the blade pressure surface in Zone III, rather than the detachment of the secondary TLV from the blade suction surface in Zone IV. These identified coherent structures provide valuable knowledge for the aerodynamic/aeroelastic effects, turbulence modeling, and reduced-order modeling of compressor tip leakage flow.

UNAFLOW: a holistic wind tunnel experiment about the aerodynamic response of floating wind turbines under imposed surge motion

Abstract. Floating offshore wind turbines are subjected to large motions due to the additional degrees of freedom of the floating foundation. The turbine rotor often operates in highly dynamic inflow conditions, and this has a significant effect on the overall aerodynamic response and turbine wake. Experiments are needed to get a deeper understanding of unsteady aerodynamics and hence leverage this knowledge to develop better models and to produce data for the validation and calibration of existing numerical tools. In this context, this paper presents a wind tunnel experiment about the unsteady aerodynamics of a floating turbine subjected to surge motion. The experiment results cover blade forces, rotor-integral forces, and wake. The 2D sectional model tests were carried out to characterize the aerodynamic coefficients of a low-Reynolds-number airfoil with harmonic variation in the angle of attack. The lift coefficient shows a hysteresis cycle close to stall, which grows in strength and extends in the linear region for motion frequencies higher than those typical of surge motion. Knowledge about the airfoil aerodynamic response was utilized to define the wind and surge motion conditions of the full-turbine experiment. The global aerodynamic turbine response is evaluated from rotor-thrust force measurements, because thrust influences the along-wind response of the floating turbine. It is found that experimental data follow predictions of quasi-steady theory for reduced frequency up to 0.5 reasonably well. For higher surge motion frequencies, unsteady effects may be present. The turbine near wake was investigated by means of hot-wire measurements. The wake energy is increased at the surge frequency, and the increment is proportional to the maximum surge velocity. A spatial analysis shows the wake energy increment corresponds with the blade tip. Particle image velocimetry (PIV) was utilized to visualize the blade-tip vortex, and it is observed that the vortex travel speed is modified in the presence of surge motion.

Development of a mathematical relationship for prediction of mixing quality in industrial convective batch mixers

This study focuses on the effects of bed-height and number of revolutions on the granular mixing performance with an objective to derive a mathematical relationship between mixing performance and number of revolutions. The simulations were carried out in a rectangular box in which three fill-levels and up to 15 blade revolutions were used. Blade forces were observed to have a direct relationship with the fill-level while mixing performance had an inverse relation and decreased with the increase in fill-level or bed-height. Mixing performance increased with the increase in the number of revolutions almost exponentially in the beginning. After around 12 blade-passes, the change in mixing performance was not significant, i.e., the mixing index value reached an asymptotic value. A mathematical relationship was derived for a quick estimate of mixing performance after given number of revolutions. The findings are significant and have direct industrial applications as they can best predict the mixing efficiency and residence times for the mixer. The proposed mathematical relationship can be effectively used for any industrial batch mixer employing blade movement or rotation and reduce the mixing costs by a significant factor.

Effects of Tip Speed Ratios on the Blade Forces of a Small H-Darrieus Wind Turbine

Lift force is an important parameter for the performance evaluation of an H-Darrieus wind turbine. The rotational direction of the streamlined force is effective on the performance of the wind turbine. In order to analyze the flow characteristics around the turbine blades in real-time, a numerical analysis using three-dimensional unsteady Reynold-averaged Navier–Stokes equations has been introduced. Experimental data were obtained from a field test facility constructed on an island in South Korea and was introduced to compare the numerical simulation results with measured data. The optimum tip speed ratio (TSR) was investigated via a multi-variable optimization approach and was determined to be 3.5 for the NACA 0015 blade profile. The turbine displays better performance with the maximum power coefficient at the optimum TSR. It is due to the delay in the flow separation from the blade surface and the relatively lower strength of the tip vortices. Furthermore, the ratio between lift and drag forces is also the highest at the optimum TSR, as most of the aerodynamic force is directly converted into lift force. For one rotation of the turbine blade at the optimum TSR, the first quarter of motion produces the highest lift as the static pressure difference is maximum at the leading edge, which helps to generate maximum lift. At a TSR less than the optimum TSR, small-lift generation is dominant, whereas at a higher TSR, large drag production is observed. Both of these lead to lower performance of the turbine. Apart from the TSR, the optimum wind angle of attack is also investigated, and the results are prepared against each TSR.

Influence of jet flow on the hydrodynamic and noise performance of propeller

The non-uniformity of the propeller wake field will lead to noise deterioration and structural strength problems of the underwater vehicles. Therefore, the study of jet flow technology is of great significance for improving the uniformity of the wake field and reducing vibration and noise. In this study, the Reynolds-averaged Navier–Stokes method and Ffowcs Williams and Hawkings acoustic model are used together to ascertain the influence of jet flow on the hydrodynamic and noise performance of the propeller. The accuracy of the numerical simulation method is verified through the convergence analysis of the calculation results. The hydrodynamic performance of the submarine and propeller with jet flows on different parameters is studied. The results show that the triangular jet can significantly improve the non-uniformity of the circumferential distribution of the wake field at the propeller plane and reduce the dynamic bearing force of the propeller blade. Simultaneously, the spectrum analysis of the numerical simulation results of the propeller noise shows that, compared with the no jet condition, the total sound pressure level at the propeller plane in the low-frequency range can be reduced by more than 3 dB using jet flow in front of the propeller. Hence, the low-frequency discrete spectrum noise of the submarine propeller can be better controlled.

Validation of wind turbine wakes modelled by the Meso-NH LES solver under different cases of stability

In wind farms, the wakes of upstream turbines impact the downstream ones in terms of power production, loads, and fatigue. The wake properties depend on many parameters such as the stratification, Coriolis force, large-scale forcing and orography. To simulate this interdependence, the actuator line method (ALM) has been implemented in the atmospheric code Meso-NH, which is an LES research code developed by the French weather services. This implementation has already been validated for the blade force distribution on the NewMexico case (uniform inflow in a wind tunnel) and for the interaction with the atmosphere on the Horns Rev photo case. The work presented here aims at completing the validation in a realistic atmospheric boundary layer (ABL), with a focus on velocity deficit and wake meandering. It is based on the international SWiFT benchmark which compares the results of many numerical models with LiDAR measurements in the wake of a single turbine for three cases of atmospheric stability: neutral, unstable and stable. The good results show the capacity of Meso-NH/ALM to generate realistic wakes in a representative ABL.

The Influence of Blade Type and Feeding Force during Resin Bonded Dentin Specimen Preparation on the Microtensile Bond Strength Test.

This paper presents the effect of blade type and feeding force during resin-bonded dentin specimen preparation on the microtensile bond strength (μTBS) test. Forty resin-bonded flat middle dentin specimens were divided into four groups. The specimens of each group were sectioned according to type of blade and feeding force as follows: fine grit/20 N, fine grit/40 N, medium grit/20 N, and medium grit/40 N to obtain resin-dentin sticks with a cross-sectional area of 1.0 mm2. Four sticks from the center of each tooth were subjected to the μTBS test. Five remaining sticks of each group were selected for surface topography observation under a scanning electron microscope (SEM). As a result, the bond strength of the medium-grit group was higher than that of the fine-grit group (p < 0.001), whereas the feeding force had no influence on bond strength values (p = 0.648). From the SEM, sticks prepared with the fine-grit blade showed a smoother surface integrity and fewer defects on the specimen edges in comparison with the sticks prepared with the medium-grit blade. The grit type of the blade is one of the considerable factors that may affect the bond strength and the surface integrity of resin-dentin specimens for microtensile testing.