Blade Curvature Research Articles

Velocity Measurement of Flow Around Model Vertical Axis Wind Turbines

A study of the air flow around five different model vertical axis wind turbines has been undertaken using Particle Image Velocimetry (PIV) in a closed loop wind tunnel. Turbine models include a ‘standard Savonius’ design, a ‘deep’ blade and a ‘shallow’ blade and two blades with compound blade curvature. Measurements were obtained at six constant phase angles of the turbine rotor. Large scale flow structures are evident in all designs such as vortices shed from blade surfaces. Results show the rotor relies on lift forces. Further analysis shows that there is considerable interaction between flow over the forward blade and the wake of the trailing blade.

A mathematical model of the oar blade – water interaction in rowing

Our aim was to present a mathematical model of rowing and sculling that allowed for a comparison of oar blade designs. The relative movement between the oar blades and water during the drive phase of the stroke was modelled, and the lift and drag forces generated by this complex interaction were determined. The model was driven by the oar shaft angular velocity about the oarlock in the horizontal plane, and was shown to be valid against measured on-water mean steady-state shell velocity for both a heavyweight men's eight and a lightweight men's single scull. Measured lift and drag force coefficients previously presented by the authors were used as inputs to the model, whichs allowed for the influence of oar blade design on rowing performance to be determined. The commonly used Big Blade, which is curved, and it's flat equivalent were compared, and blade curvature was shown to generate a 1.14% improvement in mean boat velocity, or a 17.1-m lead over 1500 m. With races being won and lost by much smaller margins than this, blade curvature would appear to play a significant role in propulsion.

Aerodynamics of swept and leaned transonic compressor-rotors

A systematic investigation to understand the impact of axially swept and tangentially leaned blades on the aerodynamic behaviour of transonic axial-flow compressor rotors was undertaken. Effects of axial and tangential blade curvature were analyzed separately. A commercial CFD package, which solves the Reynolds-averaged Navier–Stokes equations, was used to compute the complex flow field of transonic compressor-rotors. It was validated against NASA Rotor 37 existing experimental data. Computed performance maps and downstream profiles showed a good agreement with measured ones. Furthermore, comparisons with experimental data indicated that the overall features of three-dimensional shock structure, shock-boundary layer interaction, and wake development are calculated well by the numerical solution. Next, quite a large number of new transonic swept rotors (26) were modelled from the original Rotor 37, by changing the meridional curvature of the original stacking line through three previously defined control points (located at 33%, 67% and 100% of span). Similarly, 26 new transonic leaned rotors were modelled by changing the circumferential position of the same control points. All the new transonic rotors were simulated and the results revealed many interesting aspects which are believed to be very helpful to better understand the blade curvature effects on shock structure and secondary losses within a transonic rotor.

An experimental investigation on dimensional stability of injected wax patterns of gas turbine blades

An experimental study on dimensional stability of simplified waxed models of gas turbine blade is presented. Gas turbine blades, made of a super alloy, have narrow dimensional and geometrical tolerances. Blades are manufactured by investment casting process consisting of wax injection, ceramic coating, wax removal, metal casting, and finishing. The dimensional accuracy of wax injection step introduces a great influence on the final blade dimension and thus on finishing process. The focus of this experimental work was on the injection stage, investigating the effects of processing parameters and blade geometrical features on the shrinkage of critical dimensions. To reduce the complexity of the analysis and mold manufacture, two designed models were extracted from the blade geometry. A mold was manufactured with two cavities (for two models). Injection temperature and holding time were chosen as variable processing parameters. The results indicated that the effect of blade curvature and non-uniform thickness are noticeably different. The effect of the holding time was found to be more dominant than that of the injection temperature.

Computational studies of flow through cross flow fans - effect of blade geometry

This present paper describes three dimensional computational analysis of complex internal flow in a cross flow fan. A commercial computational fluid dynamics (CFD) software code CFX was used for the computation. RNG k-e two equation turbulence model was used to simulate the model with unstructured mesh. Sliding mesh interface was used at the interface between the rotating and stationary domains to capture the unsteady interactions. An accurate assessment of the present investigation is made by comparing various parameters with the available experimental data. Three impeller geometries with different blade angles and radius ratio are used in the present study. Maximum energy transfer through the impeller takes place in the region where the flow follows the blade curvature. Radial velocity is not uniform through blade channels. Some blades work in turbine mode at very low flow coefficients. Static pressure is always negative in and around the impeller region.

Untersuchung einer Axialturbinen-Stufe mit tangential gekrümmten Leitschaufeln - Teil I: Strömungsstruktur im Leitradkanal

By tangential curvature of the stacking line of the blade profiles guide vanes can be designed, which have on both ends an obtuse angle between suction side and sidewall. This configuration, according to literature, is capable of reducing the secondary loss. This type of vanes, because of the resulting radial components of the blade force, effects a radial displacement of the meridional stream-lines, a modification of the pressure distributions on the profiles and different flow outlet angles. Three-dimensional numerical simulations with the Navier-Stokes-solver Numeca have been made for a single stage axial turbine with different types of tangentially curved guide vanes. The effects of the blade curvature on the flow field and the blade forces have been investigated systematically and in detail.

Towards a generic architectural model of tillering in Gramineae, as exemplified by spring wheat (Triticum aestivum)

This paper presents an architectural model of wheat (Triticum aestivum), designed to explain effects of light conditions at the individual leaf level on tillering kinetics. Various model variables, including blade length and curvature, were parameterized for spring wheat, and compared with winter wheat and other Gramineae species. The architectural model enables simulation of plant properties at the level of individual organs. Parameterization was based on data derived from an outdoor experiment with spring wheat cv. Minaret. Final organ dimensions of tillers could be modelled using the concept of relative phytomer numbers. Various variables in spring wheat showed marked similarities to winter wheat and other species, suggesting possibilities for a general Gramineae architectural model. Our descriptive model is suitable for our objective: investigating light effects on tiller behaviour. However, we plan to replace the descriptive modelling solutions by physiological, mechanistic solutions, starting with the localized production and partitioning of assimilates as affected by abiotic growth factors.

Three-dimensional flow analysis and improvement of slip factor model for forward-curved blades centrifugal fan

This work developed improved slip factor model and correction method to predict flow through impeller in forward-curved centrifugal fan. Both steady and unsteady three-dimensional CFD analyses were performed to validate the slip factor model and the correction method. The results show that the improved slip factor model presented in this paper could provide more accurate predictions for forward-curved centrifugal impeller than the other slip factor models since the present model takes into account the effect of blade curvature. The correction method is provided to predict mass-averaged absolute circumferential velocity at the exit of impeller by taking account of blockage effects induced by the large-scale backflow near the front plate and flow separation within blade passage. The comparison with CFD results also shows that the improved slip factor model coupled with the present correction method provides accurate predictions for mass-averaged absolute circumferential velocity at the exit of impeller near and above the flow rate of peak total pressure coefficient.

Genotypic variation of leaf characteristics of wild populations of Cordyline australis (Lomandraceae) in New Zealand

Observations were made on the size, shape, and colour of leaves of 5‐ to 6‐year‐old trees of Cordyline australis (cabbage tree, ti kouka) raised from seed of 28 wild populations from a 12° latitudinal range in New Zealand and grown under uniform garden conditions at Lincoln (43°38'S, 172°43'E). Overall, mean population linear leaf dimensions increased, leaves became broader, and petioles were less defined the further south the population origin. These genotypic patterns were correlated with matching leaf phenotypic characteristics of trees at their source locations. Latitudinally related clines of variation were also shown for leaf colour states and states defining transverse curvature of leaf blades. Blade thickness, purple leaf‐base coloration, and midrib distinc‐tiveness showed regional foci of variation. Character distribution patterns indicate centres of variation in northern North Island and northern South Island. The variations of the leaf character states are discussed in relation to adaptation to irradiance and water availability. It is concluded that the variation observed is adequately described genecologically as predominantly continuous and clinal along ecological gradients, and regional discontinuities in the occurrence of character states do not merit taxonomic categorisation. The study supports in situ conservation of genetically distinct C. australis populations across the species range and emphasises the importance of using locally sourced seed where the species is planted to restore native plant communities.

Flow field investigations in centrifugal pumps with simple blade curvature and constant impeller width by means of digital particle image velocimetry

Flow field investigations in centrifugal pumps with simple blade curvature and constant impeller width by means of digital particle image velocimetry

Effect of Film Hole Row Location on Film Effectiveness on a Gas Turbine Blade

Experiments were performed to study the effect of film hole row location on local film effectiveness distribution of a turbine blade model with air or CO2 film injection. Tests were performed on a five-blade linear cascade at the chord Reynolds number of 3.0 × 105 at the cascade inlet. A combination of turbulence grid and unsteady wake was used to create a higher free-stream turbulence level. The test blade had three rows of film holes in the leading edge region and two rows each on the pressure and suction surfaces. Film hole row locations were set by leaving the film holes at that row location open and covering the remaining rows. In addition, the additive nature of film cooling on the turbine blade model was examined by comparing the measured film effectiveness with the predicted effectiveness from the superposition method. Results show that injection from a different film hole row location provides a different effectiveness distribution on pressure and suction surfaces depending on local mainstream velocity and blade curvature. In most cases, the superposition method holds downstream of the last film hole row.

Optimization of impeller design for gas inducing type mechanically agitated contactors

AbstractRates of gas induction and fractional gas hold‐up were measured in a 0.57 m i.d. gas inducing type mechanically agitated contactor. Several designs of the impeller were employed for optimizing the rate of gas induction with respect to power consumption. The effect of blade width blade, angle, blade thickness, blade curvature, number of blades, etc. on gas induction, has been investigated in detail. An optimum design has been proposed. Hysteresis in the gas induction rate and power consumption was observed for a wider impeller projecting out of stator.

Theoretical analysis of inertially irrotational and solenoidal flow in two-dimensional radial-flow pump and turbine impellers with equiangular blades

Using the theory of functions of a complex variable, in particular the method of conformal mapping, the irrotational and solenoidal flow in two-dimensional radialflow pump and turbine impellers fitted with equiangular blades is analysed. Exact solutions are given for the fluid velocity along straight radial pump and turbine impeller blades, while for logarithmic spiral pump impeller blades solutions are given which hold asymptotically as (r1/r2)n→0, in whichr1is impeller inner radius,r2is impeller outer radius andnis the number of blades. Both solutions are given in terms of a Fourier series, with the Fourier coefficients being given by the (Gauss) hypergeometric function and the beta function respectively. The solutions are used to derive analytical expressions for a number of parameters which are important for practical design of radial turbomachinery, and which reflect the two-dimensional nature of the flow field. Parameters include rotational slip of the flow leaving radial impellers, conditions to avoid reverse flow between impeller blades, and conditions for shockless flow at impeller entry, with the number of blades and blade curvature as variables. Furthermore, analytical extensions to classical one-dimensional Eulerian-based expressions for developed head of pumps and delivered work of turbines are given.

Analysis of Flow within Pump Impeller of Torque Converter.

It is very difficult to measure the flow patterns within rotating elements of a torque converter due to the complicated construction. In this study, three-dimensional incompressible turbulent flow within a pump impeller of a torque converter was analyzed numerically at three different speed ratios between the pump and the turbine. The governing equations involving the standard k-ε model in the physical component tensor form were solved with a boundary-fitted coordinate system fixed on the rotating impeller. The computed results were compared with those obtained by the flow visualization and good agreement between them was obtained. Moreover, the results at the three speed ratios were also examined in order to clarify the behavior of secondary flow patterns in detail. The results showed that the structures of secondary flow patterns were influenced by the correlations among the intensities of the Coriolis force and the centrifugal forces caused by the passage curvature in the meridional plane and the blade curvature on the blade-to-blade surface.

Advanced direct-design procedure for centrifugal impellers

The design of centrifugal impellers usually starts with a preliminary design making use of one-dimension al flow analysis thus enabling the skeletal dimensions of the impeller to be determined. This is followed by a detailed design that requires the complete description of the three-dimensional geometry which is subsequently modified by means of successive aerodynamic analysis (indirect approach). The initial description of the blade geometry relies heavily on the experience and the engineering judgement of the designer. This article will present a method that will replace this arbitrary stage of the design sequence by a design procedure that will effectively generate the three-dimensional coordinate of impellers designed for a prescribed velocity schedule (direct-design approach). The study suggests that the degree of blade wrapping could—and was controlled by—adjusting the magnitude and the distribution characteristics of the relative pressure loading parameter. The leaning of the mean streamline forward is caused by increasing the loading distribution while a backward lean is achieved by decreasing the blade loading. The rate at which the radial relative velocity accelerates was used to eliminate undesirable blade curvatures during the design procedure.

An Experimental Study of Local Wall Shear Stress, Surface Static Pressure, and Flow Visualization Upstream, Alongside, and Downstream of a Blade Endwall Corner

The experimental study reported in this paper was performed to acquire information on the distribution of wall shear stress and surface static pressure in a blade endwall corner. The blade endwall corner region investigated was divided into three sections: 0.4 chord length upstream of the blade leading edge, inside the endwall corner region, and one chord length downstream of the blade trailing edge. The maximum increases in the values of wall shear stress were found to exist on the endwall, in the corner region, between the blade leading edge and the location of maximum blade thickness (≈ 140 percent maximum increase, compared to its far upstream value, at x/D = 6). Surface flow visualization defined the boundaries of the vortex system and provided information on the direction and magnitude of the wall shear stress. The acquired results indicated that the observed variations of wall shear stress and surface static pressure were significantly influenced by the interaction of secondary flows with pressure gradients induced by the presence of blade curvature.

Ergonomics in sickle operation

Sickle operation in harvesting has been analysed with reference to design features of nine different types of sickles, and field and laboratory based investigations on biomechanical stresses and physiological valuation on six farmers. It has been indicated that the blade geometry contributes significantly to human performance and there is ample scope for further design optimisation. The suggested modifications are: (i) sickle weight — 200 g; (ii) total length of sickle — 33 cm; (iii) handle length — 11 cm; (iv) handle diameter — 3 c cm; (v) radius of blade curvature — 15 cm; (vi) blade concavity — 5 cm; (vii) serrated sickle: tooth pitch — 0.20 cm and tooth angle — 60 degrees; (viii) ratio of the length of cutting surface to chord length — 1·20.

Flow at the Tip of a Forward Curved Centrifugal Fan

The velocity profiles, radial and circumferential components, were measured at the tip of a forward curved centrifugal fan. Three sets of measurements are presented. Two at peak efficiency for different rotational speeds and a third at the lower rotational speed and for a reduced flow rate.A reverse flow region was formed near the hub, and almost in the middle, between pressure and suction sides of the blade. Near the shroud a high velocity region was observed and a low one near the suction side, picture similar to the jet-wake structure found in the literature.At the lower rotational speed and low flow rate the flow was affected mainly by the system rotation. A “wake” was formed along the suction side of the blade. Increasing the flow rate blade curvature effects became more dominant.Increasing the rotational speed and for the same flow coefficient the system of two vortices observed in the previous case disappears and a single vortex takes its place. In this case the wake is positioned on the hub.Corner vortices also affect the main flow by changing the turbulence intensities. A corner vortex observed on the pressure side reduced the turbulence intensities in the region and a wake was formed locally. However, another corner vortex on the suction side caused an increase to the local turbulence intensities and consequently a high local velocity.Copyright © 1984 by ASME

Navier–Stokes Solutions of Unsteady Flow in a Compressor Rotor

In order to achieve more accurate predictions of unsteady flow in a transonic compressor rotor an existing numerical approach has been modified by incorporating a turbulence model. The computations are performed by solving the complete time-dependent compressible Navier–Stokes equations using MacCormack’s explicit finite difference algorithm. These equations are solved for the flow through two adjacent rotor blades at a streamsurface near the blade tip subjected to the wakes emitted from upstream stators. At this radial location the flow enters the blade passage at an absolute Mach number of 0.66. The high blade curvature at this radial location produces a large region of separated flow on the suction surface with laminar flow. To more accurately resolve the features of this flow separation the Baldwin–Lomax algebraic eddy-viscosity turbulence model is incorporated into the numerical procedure in regions near the blade surface. The unsteady flow features are represented at the inflow boundary through the use of characteristic variables involving the upstream and downstream running Riemann invariants and the entropy variation expressed in terms of the total pressure profile. At the outflow boundary the concept of a “second throat” or choke point is implemented in conjunction with supersonic outflow conditions. The results are compared with numerical results obtained without the use of a turbulence model (laminar) for a single blade passage. Improved agreement with limited experimental data is also noted.

A Consideration of Blade and Flake Curvature

A method for characterizing blade and flake curvature is introduced and discussed in the context of broader prehistoric behavioral interpretation. The curvature value begins with interval measureme...