Actual Blade Research Articles

Thermo-flow characteristics and air flow field leading of the air-cooled condenser cell in a power plant

Special A-frame geometry of the air-cooled condenser cell and the complicated flow field at the exit of the axial flow fan bring on the air mal-distribution on the surface of the finned tube bundles and the deteriorated thermo-flow performances of a condenser cell. It is of benefit to the design and operation optimization of the direct dry cooling system in a power plant to investigate the thermo-flow characteristics of the condenser cell and propose the flow leading measures of cooling air. On the basis of the representative configuration of the air-cooled condenser cell in a 600 MW direct dry cooling power plant, the computational models of the air side fluid and heat flows are built, in which the actual fan blade geometric details are considered. Various flow field leading ways of cooling air are presented and the thermo-flow characteristics in the A-frame condenser cell and through the finned tube bundles are compared. Results show that the flow field leading measures can result in the increased volumetric flow rate and heat rejection, thus bringing on the improved performance of the condenser cell. The improvement of thermo-flow performances depends upon the geometric details of the flow guiding device.

Characteristics of lightning strikes on wind turbine blades. Experimental study of the effects of receptor configuration and other parameters

AbstractThe characteristics of lightning strikes on wind turbine blades have been investigated by model experiments with real turbine blades. The effects of various types of receptors, the polarities of the applied voltages, and pollution on the blade surface are clarified. Based on these experimental results, lightning protection design of actual wind turbine blades by receptors is discussed. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(3): 8–18, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21143

Laboratory Tests of a Hybrid Metal-Composite Transport Helicopter Blade Segment

Experimental acquisition and verification of structural properties of an actual helicopter main rotor blade segment have been done with an aim to validate the capability of bonded joints of these structural elements to sustain the most dominant dynamic loads in forward flight, for the assigned blade’s life time. It was also one of the qualitative tests of the newly applied rotor blade hybrid structure production technology, consisting of a metal spar and 21 plastic composite segments, bonded to it after the polymerization process. Because of the structural similarity of the segments, only the most highly loaded 21st segment and adjacent spar section were investigated, as representative in this particular sense. This has enabled remarkable reduction both in time and funds required for the design and construction of the test facility. This paper is focused on the demonstration of usage of fairly low-cost experimental infrastructure for that purpose, and also provides the designers and engineers with some examples and guidelines of how it is possible to conduct experimental verifications of the properties of similar, both aeronautical and non-aeronautical hybrid structures and joints, exposed to the long-lasting dynamic loads. Tests presented in this paper were only a part of a very wide test campaign, mostly undertaken on the entire new hybrid blade structures, both on the ground and in flight, before they have been put to operational service.

Evaluation of shear flow in composite wind turbine blades

The present work addresses the evaluation of the shear flow as an extension of the Jourawski’s formula. This idea is developed here for the case of a multi-celled composite thin-walled section. Firstly, the explicit formulation of the shear flow due to shear forces and torsion is derived, noting the simplificative hypothesis adopted. Then, the implemented model is verified by means of a benchmark problem with a known analytical solution. Finally, this model is utilized to evaluate the shear flow on an actual blade configuration, comparing the results obtained with those of a Finite Element model of the same blade, with a similar discretization.

Tone Noise Prediction of a Propeller Operating in Nonuniform Flows

aerodynamic sources to be integrated over the actual blade surface, rather than over the mean-chord surface. The prediction of the radiated far-field tonal noise for a four-bladed propeller operating in a nonuniform mean flow is performed. Validation of the method is presented through a detailed comparison between numerical predictions of the far-field noise and the measured data, in which excellent agreement is obtained, both in magnitude and directivity. This paper concludes that for first harmonic noise, matching the number of the main inflow harmonic of nonuniform flow with blade number creates a dipole-type symmetric directivity pattern, and mismatching appears as an asymmetric directivity pattern. Effects of a single inflow harmonic on the far-field radiated tonal noise are also quantified in this paper, which shows that when the matching condition is satisfied, the main inflow harmonic contributes most of the total radiated sound pressure, except at locations normal to the propeller axis. When the matching condition is not satisfied, however, the total radiated sound pressure is mainly caused by the dominant inflow harmonic and the inflow harmonic that equals the blade number.

OS0705 ガスタービン動翼用Ni基DS超合金の多軸熱疲労寿命(OS7-1 高温・寿命,OS-7 多軸応力下における疲労損傷および疲労き裂進展1)

In this study, biaxial thermo-mechanical fatigue (TMF) tests simulating actual blade loading condition have been carried out using a directionally solidified super alloy which is typically used in 1300C class gas turbine blades. Fatigue lives under biaxial TMF life could not be correlated with Mises equivalent strain range. An equivalent shear strain range for the Ni based DS superalloy was derived based on Γ-plane theory, and the biaxial TMF life was well correlated with the equivalent shear strain range. It was found that fatigue life was reduced to 1/5 by introducing 6 minutes strain hold time at the maximum temperature. This life reduction may be occurred due to increasing of tensile stress during strain hold period.

A Fiber Bragg Grating-Based All-Fiber Sensing System for Telerobotic Cutting Applications

A fiber Bragg grating (FBG)-based strain sensing system for minimally invasive telerobotic cutting applications is presented in this paper. Investigations assume that a scissor blade can be approximated as a uniformly tapered cantilever beam. A replica of the scissor blade is produced and strain characterization has been carried out using an FBG sensor system. Results are validated against measurements obtained using conventional electrical resistance strain gauges. The scissor blade experiences both direct and lateral forces during cutting, hence the system is characterized for a direct load range of 0-30 N and a lateral load range of 0-10 N. The results show a very good linear response for direct loading and some sensitivity to lateral loading. An actual sensorized scissor blade prototype is also characterized and results compared with that of the replica blade. The FBG interrogation system used was a macro-bend fiber filter-based ratiometric system. The use of FBGs together with macro-bend fiber-based interrogation system eliminates the influence of temperature on the sensing system and hence temperature independent strain information from the blade is obtained. The results obtained using the macro-bend fiber filter are compared with that of a commercial interrogation system and found to be in agreement. By implementing an all fiber sensing system based on fiber Bragg gratings and macrobend fiber filter interrogation system, remote operation of telerobotic cutting applications can be made more cost effective while providing a competitive accuracy and resolution solution.

A Methodology for Predicting the Response of Blades With Nonlinear Coatings

Ceramic coatings applied by air plasma spray or electron beam techniques as thermal barrier coatings or to improve the erosion or corrosion resistance of blades in gas turbine engines are found to add damping to the system. However, such coatings display nonlinear mechanical properties in that the Young’s modulus and the measure of damping are dependent on the amplitude of cyclic strain. To account for the coating nonlinearity, a new methodology for predicting blade response was developed and applied to an actual component coated with a titania-alumina blend ceramic infiltrated with a viscoelastic material. Resonant frequencies, mode shapes, and the forced response of a one blade segment of an integrated disk from a fan stage rotor were computed and compared with results from bench tests. Predicted frequencies agreed satisfactorily with measured values; predicted and observed values of system damping agreed to within 10%. The results of these comparisons are taken to indicate that it is possible to use laboratory-determined material properties together with an iterative finite element analysis to obtain satisfactory predictions of the response of an actual blade with a nonlinear coating.

Heat Transfer and Pressure Drop Measurements for a Square Channel With 45 deg Round-Edged Ribs at High Reynolds Numbers

Experiments to determine heat transfer coefficients and friction factors are conducted on a stationary 45 deg parallel rib-roughened square channel, which simulates a turbine blade internal coolant passage. Copper plates fitted with silicone heaters and thermocouples are used to measure regionally averaged heat transfer coefficients. Reynolds numbers studied range from 30,000 to 400,000. The ribs studied have rounded (filleted) edges to account for manufacturing limitations of actual engine blades. The rib height (e) to hydraulic diameter (D) ratio (e/D) ranges from 0.1 to 0.2, while spacing (p) to height ratio (p/e) ranges from 5 to 10. Results indicate an increase in the heat transfer due to the ribs at the cost of a higher friction factor, especially at higher Reynolds numbers. Round-edged ribs experience a similar heat transfer coefficient and a lower friction factor compared with sharp-edged ribs, especially at higher values of the rib height. Correlations predicting Nu and f as a function of e/D, p/e, and Re are presented. Also presented are correlations for the heat transfer and friction roughness parameters (G and R, respectively).

Broadband rotor noise prediction based on a new frequency-domain foumulation

This article studies the broadband noise of a rotor in upstream turbulence. A numerical approach is proposed, based on frequency domain, for predicting rotor broadband noise which requires the aerodynamic sources to be integrated over the actual blade surface rather than over the mean-chord surface. The prediction of the radiated rotor broadband noise due to turbulence is made. This method is validated through a comparison between numerical predictions and measured data, with a reasonable agreement. Noise level directivity shows that the main lobe is located along the rotor axis, while the minimum noise occurs in the direction vertical to the rotor axis.

Spatial structure of a turbulent boundary layer with irregular surface roughness

Particle image velocimetry experiments were performed to study the impact of realistic roughness on the spatial structure of wall turbulence at moderate Reynolds number. This roughness was replicated from an actual turbine blade damaged by deposition of foreign materials and its features are quite distinct from most roughness characterizations previously considered as it is highly irregular and embodies a broad range of topographical scales. The spatial structure of flow over this rough surface near the outer edge of the roughness sublayer is contrasted with that of smooth-wall flow to identify any structural modifications due to roughness. Hairpin vortex packets are observed in the outer layer of the rough-wall flow and are found to contribute heavily to the Reynolds shear stress, consistent with smooth-wall flow. While similar qualitative consistency is observed in comparisons of smooth- and rough-wall two-point correlations, some quantitative differences are also apparent. In particular, a reduction in the streamwise extent of two-point correlations of streamwise velocity is noted which could be indicative of a roughness-induced modification of outer-layer vortex organization. Proper orthogonal decomposition analysis reveals the streamwise coherence of the larger scales to be most sensitive to roughness while the spatial characteristics of the smaller scales appear relatively insensitive to such effects.

Harmonic Balance Analysis of Blade Row Interactions in a Transonic Compressor

In this paper we apply the harmonic balance technique to analyze an inlet guide vane and rotor interaction problem, and compare the computed flow solutions to existing experimental data. The computed results, which compare well with the experimental data, demonstrate that the technique can accurately and efficiently model strongly nonlinear periodic flows, including shock/vane interaction and unsteady shock motion. Using the harmonic balance approach, each blade row is modeled using a computational grid spanning just a single blade passage regardless of the actual blade counts. For each blade row, several subtime level solutions that span a single time period are stored. These subtime level solutions are related to each other through the time derivative term in the Euler (or Navier―Stokes) equations, which is approximated by a pseudo-spectral operator, by complex periodicity conditions along the periodic boundary of each blade row's computational domain, and by the interface boundary conditions between the vane and rotor. Casting the governing equations in harmonic balance form removes the explicit dependence on time. Mathematically, the equations to be solved are similar in form to the steady Euler (or Navier―Stokes) equations with an additional source term proportional to the fundamental frequency of the unsteadiness. Thus, conventional steady-state computational fluid dynamics techniques, including local time stepping and multigrid acceleration, are used to accelerate convergence, resulting in a very efficient unsteady flow solver.

243 自動車用ワイパブレードの反転挙動における分岐現象(実験,OS-21 機械・構造物における非線形振動とその応用,総合テーマ「伝統を,未来へ!」)

Recently, wiping performance simulation and theoretical analysis of a wiper is desired to streamline the development of it. This research aims to describe the dynamics of the reversal behavior of the wiper blade. First, the experiment with the cut model of actual blade rubber was conducted to observe the reversal behavior of wiper blade. To theoretically identify the mechanism, governing equations are derived from the analytical model of wiper blade which consists of a rigid bar. Bifurcation produced in the reversal behavior is discussed with the equation of equilibrium focusing on the friction acting the rubber.

Experimental Study of Heat Transfer in Gas Turbine Blades Using a Transient Inverse Technique

To enhance specific power output and thermal efficiency of gas turbine engines, industry searches for ways to increase the turbine inlet temperatures. Therefore, temperatures of turbine blades increase as well and necessitate active cooling of these components. Experimental design work on such internal cooling schemes is carried out to find acceptable compromises between heat transfer and pressure losses. It is often carried out by using transient thermochromic liquid crystal techniques in combination with Plexiglas models. However, for real turbine blades this experimental technique is inappropriate due to the lack of optical access. Therefore, to study actual turbine blades there is need for development of noninvasive, nondestructive methodologies. This article describes a measurement technique that allows determination of internal heat transfer coefficients of real turbine blades experimentally. Thus, a test rig with a rapidly responding heater was designed to fulfill the requirement of a sudden increase in the air temperature within the cooling passages. The outer surface temperatures were measured using infrared thermography. To estimate the spatial distribution of internal heat transfer coefficients from transient surface temperatures the inverse heat transfer problem was solved. As optimization algorithm the Levenberg–Marquardt method was chosen. Outer surface temperature data was measured for a rectangular reference model with rib turbulators and compared with simultaneously acquired data using the thermochromic liquid crystal technique. It is concluded that the new experimental measurement technique could be used to quantitatively determine internal heat transfer coefficients.

A model to determine the theoretical maximum feed speed of a frame saw

The frame saw is a popular primary and secondary log breakdown saw in South Africa. In this study a theoretical model for estimating the maximum feed speed of a frame saw is derived. Contrary to earlier models, the actual blade speed is used as a variable in the derivation. The chip holding capacity of the saw gullet is used as the limiting factor for feed speed. The model was evaluated in a trial at an industrial saw mill. The results from the sawing variation trial support the validity of the model. In the case where the feed speed was above the calculated theoretical maximum value, sawing variation increased significantly.

Lightning Striking Characteristics to Wind Turbine Blades -Experimental Study of Effects of the Receptor Configuration and Other Parameters-

Lightning striking characteristics to wind turbine blades have been investigated by the model experiments with actual turbine blades. The effects of various types of receptors, polarities of applied voltages, pollution on the blade surface have been clarified. Based on these experimental results, lightning protection design of actual wind turbine blades by receptors has been discussed.

Familial Risk Of Kidney Cancer

Gravity and centrifugal investment casting processes of low-pressure turbine blades with high Nb–TiAl alloy were simulated by Procast software. Actual blade components were poured by vacuum induction suspended furnace with Ar protection. The experimental verification indicated that the simulation results were in good agreement with the experimental results. Comparative results had shown that the surface of centrifugal casting blade was more complete than that of gravity casting one. In gravity casting process, molten metal filled the thinnest trailing edge at last, resulting in the generation of misrun defects. Furthermore, the shrinkage porosity and crack defects of gravity casting were much more and dispersive. The internal and external quality of centrifugal casting was much better than that of gravity casting. Microstructures from edge to center of gravity casting blade had no significant change. The microstructure for centrifugal casting blade is finer than that for gravity casting blade, however, a large number of dentritic γ segregation appeared in the blade edge of centrifugal casting, which resulted from the fast cooling rate of centrifugal casting surface.

A Comparison of Approximate Versus Exact Geometrical Representations of Roughness for CFD Calculations of cf and St

Skin friction (cf) and heat transfer (St) predictions were made for a turbulent boundary layer over randomly rough surfaces at Reynolds number of 1×106. The rough surfaces are scaled models of actual gas turbine blade surfaces that have experienced degradation after service. Two different approximations are used to characterize the roughness in the computational model: the discrete element model and full 3D discretization of the surface. The discrete element method considers the total aerodynamic drag on a rough surface to be the sum of shear drag on the flat part of the surface and the form drag on the individual roughness elements. The total heat transfer from a rough surface is the sum of convection on the flat part of the surface and the convection from each of the roughness elements. Correlations are used to model the roughness element drag and heat transfer, thus avoiding the complexity of gridding the irregular rough surface. The discrete element roughness representation was incorporated into a two-dimensional, finite difference boundary layer code with a mixing length turbulence model. The second prediction method employs a viscous adaptive Cartesian grid approach to fully resolve the three-dimensional roughness geometry. This significantly reduces the grid requirement compared to a structured grid. The flow prediction is made using a finite-volume Navier-Stokes solver capable of handling arbitrary grids with the Spalart-Allmaras (S‐A) turbulence model. Comparisons are made to experimentally measured values of cf and St for two unique roughness characterizations. The two methods predict cf to within ±8% and St within ±17%, the RANS code yielding slightly better agreement. In both cases, agreement with the experimental data is less favorable for the surface with larger roughness features. The RANS simulation requires a two to three order of magnitude increase in computational time compared to the DEM method and is not as readily adapted to a wide variety of roughness characterizations. The RANS simulation is capable of analyzing surfaces composed primarily of roughness valleys (rather than peaks), a feature that DEM does not have in its present formulation. Several basic assumptions employed by the discrete element model are evaluated using the 3D RANS flow predictions, namely: establishment of the midheight for application of the smooth wall boundary condition; cD and Nu relations employed for roughness elements; and flow three dimensionality over and around roughness elements.

Computationally fast harmonic balance methods for unsteady aerodynamic predictions of helicopter rotors

A harmonic balance technique for the analysis of unsteady flows about helicopter rotors in forward flight and hover is presented in this paper. The aerodynamics of forward flight are highly nonlinear, with transonic flow on the advancing blade, subsonic flow on the retreating blade, and stalled flow over the inner portion of the rotor. Nevertheless, the unsteady flow is essentially periodic in time making it well suited for frequency domain analysis. The present method uses periodic boundary conditions that allows one to model the flow field on a computational grid around a single helicopter blade, no matter the actual blade count. Using this approach, we compute several solutions, each one corresponding to one of several instants in time over one period. These time levels are coupled to each other through a spectral time derivative operator in the interior of the computational domain and through the far-field and periodic boundary conditions around the boundary of the domain. In this paper, we apply the method to the three-dimensional Euler equations (although the method can also be applied to three-dimensional viscous flows), and examine the steady and unsteady aerodynamics about wings and rotors.

Tensile and bending thermo-mechanical fatigue testing on cylindrical and flat specimens of CMSX-4 for design of turbine blades

This paper briefly describes thermo-mechanical fatigue tests performed on cylindrical and flat specimens of the single crystal material CMSX-4 in 〈0 0 1〉, 〈0 1 1〉 and 〈1 1 1〉-orientation. The test matrix was defined based on the thermo-mechanical loading identified at different positions of actual turbine rotor blades. It included tensile strain-controlled TMF-test conditions on the cylindrical plain specimens and tensile load-controlled TMF-test conditions on the flat specimens with a variable number of straight and angled holes. Flat specimens without holes were tested under load-controlled bending TMF conditions. Different cycle types of in-phase, out-of-phase and phase-shift were applied. A summary is given about the test results including S-N-curves, fracture sections and hysteresis loops and about empirical modeling for prediction of fatigue life of the material. The developed algorithms that predicted the lives in good agreement with the experimental ones cover a large range of thermo-mechanical loading conditions and are applicable to the design of future turbine blades.