Chord Direction Research Articles

Parameter Optimization for Laser Peen Forming on 6005A-T6 Aluminum Alloy Plates to Enhance the Constrained Deformation of Integral Stiffened Plates.

Multiscale parameter optimization for laser peen forming (LPF) on 6005A-T6 aluminum alloy plates was conducted through a combination of simulation and experimentation. By obtaining the optimal parameter, this study aims to explore the constrained deformation and forming laws of the integral stiffened plates. Detailed descriptions were provided regarding the dynamic response process and transient behavior of aluminum alloy plates under ultrahigh strain rates, along with an in-depth analysis of the stress evolution. The results reveal that laser beam diameter and laser beam energy can achieve large range forming, while the number of tracks facilitates the precise deformation adjustment. During the 12-track LPF process, there is an overall upward trend in deformation values accompanied by a dynamic increase in the bend curvature. After static relaxation, the deformation value recovers to 55.2% of the final bending curvature. The chord direction scanning of stiffened plates exhibits a larger bending curvature, indicating its greater forming capacity for large-sized single unfolding direction formation; whereas, the unfolding direction scanning of stiffened plates excels in achieving efficient integrated two-way forming.

The Matching Mechanism and Flow Mechanisms of Supersonic Through-Flow Variable-Pitch Tandem Cascade

Abstract The geometric structure of the supersonic through-flow variable-pitch tandem fan poses challenges in ensuring optimal relative blade positions across various operating modes. This study employed numerical simulations to investigate the impact of axial overlap and percent pitch on the aerodynamic performance of fan in typical modes. Furthermore, it delved into the intricate interplay between the front and rear blades, offering detailed insights into the selection principles governing the relative blade positions in the supersonic through-flow variable-pitch tandem fan. The findings underscored the pivotal role of percent pitch based on chord direction in fan's aerodynamic performance. Specifically, supersonic and transonic modes exhibited superior performance when chord direction percent pitch was set at 10% and 100%, respectively. The key factor contributing to these lower losses was the influence of low-speed fluid from the wake of the front blade, which weakened the shock boundary layer interaction on the rear blade's surface. In the high-speed windmilling mode, within the confines of geometric constraints, higher percent pitch based on chord direction values corresponded to reduced losses. This outcome was primarily attributable to the gap-blocking effect, which diminished the shock boundary layer interaction on the rear blade's pressure side and improved the wake of the rear blade. However, in this mode, the loss demonstrated a positive correlation with the pressure ratio. Consequently, the selection of the relative blade position required a delicate balance between the competing demands of these two factors.

Research of biomimetic corrugation on the blade flutter suppression in large-scale wind turbine systems

Aiming at the blade flutter of large horizontal-axis wind turbines, a method by utilizing biomimetic corrugation to suppress blade flutter is first proposed. By extracting the dragonfly wing corrugation, the biomimetic corrugation airfoil is constructed, finding that mapping corrugation to the airfoil pressure side has better aerodynamic performance. The influence of corrugation type, amplitude λ, and intensity on airfoil flutter is analyzed using orthogonal experiment, which determines that the λ has the greatest influence on airfoil flutter. Based on the fluctuation range of the moment coefficient ΔC m, the optimal airfoil flutter suppression effect is obtained when the type is III, λ= 0.6, and intensity is denser (n = 13). The effective corrugation layout area in the chord direction is determined to be the leading edge, and the ΔC m of corrugation airfoil is reduced by 7.405%, compared to the original airfoil. The application of this corrugation to NREL 15 MW wind turbine 3D blades is studied, and the influence of corrugation layout length in the blade span direction on the suppressive effect is analyzed by fluid-structure interaction. It is found that when the layout length is 0.85 R, the safety margin S f reaches a maximum value of 0.3431 Hz, which is increased 2.940%. The results show that the biomimetic corrugated structure proposed in this paper can not only improve the aerodynamic performance by changing the local flow field on the surface of the blade, but also increase the structural stiffness of the blade itself, and achieve the effect of flutter suppression.

Microstructure degradation and residual low cycle fatigue life of a serviced turbine blade

AbstractThis paper was attempted to investigate the microstructure degradation and low cycle fatigue (LCF) performance of a serviced K465 Ni‐based superalloy turbine blade. LCF tests were carried out with small‐scale plate specimens sampled from the blades. Relationship between residual LCF life and microstructure state was estimated. The results indicate that the coarsening of γ/γ′ phases was the most significant microstructure degradation mode for the serviced blades. Both the γ matrix width and the γ′ precipitate diameter increased with the increase of service duration, while the γ′ precipitate volume fraction slightly decreased. The most severe microstructure degradation occurred at the leading edge along the chord direction, particularly at 50–70 % airfoil spans. The residual LCF life exhibited an accelerated decrease characteristic as increases of microstructure degradation degree. The coarsened microstructure diminished shear resistance of the superalloy, which resulted in additional accumulated inelastic deformation and a corresponding reduction in LCF life.

The Influence of Angle of Attack on the Icing Distribution Characteristics of DU97 Blade Airfoil Surface for Wind Turbines

This study explores the influence of angle of attack (AOA) on the icing distribution characteristics of asymmetric blade airfoil (DU97) surfaces for wind turbines under icing conditions by numerical simulation. The findings demonstrate a consistence between the simulated ice shapes and experimental data. The ice thickness distribution on the lower surface of the leading edge exhibits a trend of first rising and then declining along the chord direction while showing a gradually decreasing trend on the upper surface. The ice distribution range on the upper surface of the trailing edge is broader than that on the lower surface. The peak ice thickness at the trailing edge rises significantly as AOA increases from 5° to 10°, and at the leading edge raises dramatically at droplet sizes of 30–40 μm and wind speeds of 5–10 m/s. The peak ice thickness is more significantly influenced by AOA than by ambient temperature due to the combined effect of airflow characteristics induced by AOA and latent heat (phase change) and sensible heat (thermal convection and thermal radiation) caused by ambient temperature. The findings offer valuable insights into the flow and heat transfer physics, and can operate as references for wind turbine anti/de-icing technology.

Study of non-constant local cavitation suppression in micro-wedge structure

To alleviate the negative impacts of cavitation phenomenon on hydrodynamic machinery, such as mechanical vibration and noise, a hydrofoil model is established based on the micro-wedge structure, and numerical simulation of the hydrofoil is carried out by using the modified turbulence model k–omega shear stress transport (SST k–ω) to analyze the lift coefficient of drag, pressure pulsation, cavitation volume fraction, cavitation volume morphology, and turbulent kinetic energy distribution, and to reveal the inhibition of cavitation mechanism of the chord direction of the placement and the height of the micro-wedge structure coupling. The results show that the height of the micro-wedge structure determined by the thickness of the boundary layer is an important parameter affecting the cavitation performance, and the micro-wedge structure with a smaller height will produce better cavitation suppression, and the height of 0.05 mm has the best suppression effect, and the suppression of the main frequency of pulsation and the amplitude of pulsation shows a positive effect. The micro-wedge structure arranged on the hydrofoil can delay the change cycle of the cavitation volume to different degrees, in which the chordwise position of 3.5 mm has the best cavitation suppression effect, and the cavitation suppression rate is about 16.7%.

Impact of the natural structure of cortex and pith ring on water loss and deformation in bamboo processing

The function of the pith ring and cortex in biological and fluid exchanges with the surrounding environment implies a natural intelligence. Their ingenious structure enables bamboo to thrive and impacts its processing and utilization. As drying is an essential step in bamboo product manufacturing, in this study, the effects of the pith ring and cortex on the water loss, deformation, and cracking of bamboo at the macroscopic, tissue, and cellular levels were investigated. Our study revealed a previously unknown mechanism of bamboo drying deformation. The cortex significantly affected the rate of water loss, whereas the pith ring did not significantly reduce the drying rate. Three deformation mechanisms originating from the pith ring were identified: the cell structure and orientation, self-flattening during drying, and excellent bending performance in the chord direction. These pith ring characteristics led to a larger radius of the bamboo splits during drying. These findings expand our understanding of the natural intelligence of the inner and outer layers of bamboo and provide important insights into bamboo drying, deformation, cracking, bionics, and composite material manufacturing.

Partial tip air injection to extend the stall margin in an axial flow compressor with circumferential inlet distortion

As a typical non-axisymmetric inflow, circumferential pressure inlet distortion was experimentally investigated in an axial flow compressor. Based on the obvious decreasing trend of stall margin with the enhancement of distorted intensity, the stall mechanism under the condition of maximum distorted intensity, namely, 24.57 %, was studied in detailed. The casing static pressure over the rotor blade tip along the chord and circumferential direction were measured using a collection of dynamic transducers. Results show that under the circumferential inlet distortion condition, the pressure disturbance is always generated downstream from the distorted region along the rotational direction, and circumferentially propagates until it disappears in the upstream of the distorted region. With the continuous throttling, if the pressure disturbance that has not completely disappeared in the undistorted region enters the distorted region again, its energy will be enhanced, finally induces the stall. Using the above understanding as a foundation to apply partial tip air injection to suppress the disturbance caused by the circumferential inlet distortion, and resist its adverse effect on stall margin to ensure the safe operation of the compressor. It demonstrated that the tip air injection applied in the downstream of the distorted region can obtained the largest stall margin on the premise of the same injected momentum. For the strongest distortion case (DC (60) equals to 24.57 %), the injectors fixed downstream the distorted region can reduce the number and scale of the spike disturbances, suppress the local tip leakage vortex, and decrease the amplitude of the pressure disturbance energy, thus a maximum stall margin improvement of 3.18 % is obtained. However, tip air injection in the undistorted region cannot contribute the stall margin improvement that it leads to stronger tip leakage vortex and earlier stall inception. This study provides a guideline to design the non-axisymmetric tip air injection for circumferential inlet distortion with a help of injected mass flow and energy reduction.

Study on the Aerothermoelastic Characteristics of a Body Flap Considering the Nozzle–Jet Interference

A body flap/RCS-integrated configuration is often used to achieve pitch trimming and controlled flight in near space for hypersonic vehicles. Under the high temperature and pressure load induced by the expansion wave at the nozzle exit, the body flap is prone to significant structural deformation, which leads to a change in the resulting moment, even comparable to the control ability, and bring additional challenges to the control system. Based on the CFD/CTD/CSD coupling method, the aerothermoelastic effect on the aerodynamic characteristics and structural deformation of the body flap under jet interaction is systematically studied. Numerical results indicate that the pitching moment coefficients show an increasing trend for all the models, rigid, elastic and thermoelastic, while the increment significantly decreases with the increase in trajectory altitudes. With the increase in deflection angle, the pitching moment coefficients of the three models decrease nonlinearly at high altitude, and the aerothermoelastic effect significantly decreases. At a middle-lower altitudes, the pitching moment coefficient is reversed at a lager deflection angle, and the trailing edge of the body flap presents the deformation characteristics of upward bending, which makes the aerothermoelastic phenomenon degenerate into an aeroelastic problem. From the station along the chord and spanwise direction, the change in displacement increment of the thermoelastic model reflects the competitive relationship between normal stress and thermal stress imposed by jet interaction.

A stall diagnosis method based on entropy feature identification in axial compressors

AbstractA stall diagnosis method based on the entropy feature extraction algorithm is developed in axial compressors. The reliability of the proposed method is determined and a parametric sensitivity analysis is experimentally conducted for two different types of compressor stall diagnoses. A collection of time‐resolved pressure sensors is mounted circumferentially and along the chord direction to measure the dynamic pressure on the casing. Results show that the stall and prestall precursor embedded in the dynamic pressures are identified through nonlinear feature perturbation extraction using the entropy feature extraction algorithm. Further analysis demonstrates that the prestall precursor with the peak entropy value is related to the unsteady tip leakage flow for the spike‐type stall diagnosis. The modal wave inception with increasing amplitude is identified by the considerable increase of the entropy value. The flow field in the tip region indicates that the modal wave corresponds to the flow separation in the suction side of the rotor blade. The warning time is 100–300 rotor revolutions for both types of stall diagnoses, which is beneficial for stall control in different axial compressors. Moreover, a parametric study of the embedding dimension m, similar tolerance n, similar radius r, and data length N in the fuzzy entropy method is conducted to determine the optimal parameter setting for stall diagnosis. The stall warning based on the entropy feature extraction algorithm provides a new stall diagnosis approach in the axial compressor with different stall types. This stall warning can also be adopted as an online stability monitoring index when using the concept of active stall control.

Quadratic combined convective flow about yawed cylinder in presence of time variations and magnetic effects: entropy analysis

The significance of time-dependent variations in a quadratic combined convective magnetohydrodynamic (MHD) flow around an infinite yawed cylinder with entropy analysis is explored in the present investigation. There are numerous real-world applications wherein the yawed-shaped bodies are used extensively, for example, overhead cables, bridge stay cables, chimney stacks etc. First, the dimensional governing equations are made dimensionless by applying the appropriate transformations of non-similar nature. After that, using the Quasilinearization technique, the resulting equations are linearised and discretized by employing implicit finite difference approximations. In unsteady flow, velocity distributions along chordwise and spanwise directions reduced when compared with the steady case. As the cylinder's yaw angle grows, fluid pressure inside it rises, increasing its velocity in all directions. The surface drag coefficients along chord & spanwise directions and the energy transfer rate increase approximately by 104%, 67% and 40%, respectively, as R i increases from −2 to 10, for accelerating flow ( α > 0 ) at θ = 45 0 and τ = 1 . An increase in the yaw angle results in more entropy generation (EG). It shows that yawed cylinder overcomes the EG difficulties faced in the case of a vertical cylinder. It is revealed that, by using a yawed cylinder with MHD, one can restrict the amount of energy loss.

Numerical simulation of fluid-thermal structure coupling of the hypersonic wing

Taking a wing of the hypersonic aircraft as the research object, a fluid-thermal-solid coupling analysis of a two-dimensional flow around circular pipe model was simulated in MpCCI platform, which combining Fluent and Abaqus. The result was verified by the typical hypersonic flow around two-dimensional round tube unsteady experiment. It shows that the position of the shock wave and the density distribution of the flow field can be accurately calculated based on the k - ω SST turbulence model in the simulation of flow field outside the tube. The stagnation temperature of the tube is 378.7 K when T was 2s, and the relative error is 2.6% compared with the experiment. On that basis, the temperature and the stress distributions of the wing is simulated under the 2 seconds aerodynamic heating time at different Mach numbers. The results show that the wall temperature and Mises increased gradually with the increasing velocity, but the rising trend of temperature and Mises decreased gradually, and the maximum temperature appears near the leading edge of the wing, Mises decreased gradually along chord and span directions. The maximum deformation appears at the trailing edge of the wing and the elastic deformation of the whole structure is positively correlated with the temperature, and the deformed area is located at the wing tip.

Experimental Investigation of Ground Effect on the Vortical Flow Structure of a 40° Swept Delta Wing

The ground effect influences the flow structure on a delta wing during landing and take-off processes. In this regard, comprehensive instantaneous velocity measurements and flow visualizations were carried out by particle image velocimetry and dye flow visualization techniques to reveal the ground effect on leading-edge vortex characteristics of a 40° swept delta wing. The flow behaviors on the delta wing under the impact of the ground were analyzed at two angles of attack, 8° and 11°, and the space between the ground and lower surface of the wing was nondimensionalized with the wing’s chord length. It was found that the presence of the ground caused premature leading-edge vortex breakdown due to the increasing adverse pressure gradient on the wing’s suction side along the chord direction. The ground effect caused an increase in peak value and distributions of turbulent kinetic energy on the wing surface that depended on the earlier leading-edge vortex bursting and complex and disorganized flow structures. The value of time-averaged vertical velocity was lower when the delta wing descended from the free-stream flow zone into the ground effect zone because of the blocking of fluid flow in the gap between the ground and pressure surface of the wing. Thus, it can be concluded that the ground effect is very influential on the change of vortical flow characteristics of nonslender delta wings.

Simulations of flow over a bio-inspired undulated cylinder with dynamically morphing topography

Inspired by the geometric properties of seal whiskers, the addition of spanwise undulations on a cylinder have been shown to lower the mean and oscillatory forces and modify the frequency of flow-induced vibration when compared to smooth cylinders. Previously, computational fluid dynamics (CFD) has been used to characterize the hydrodynamic response with respect to specific geometric features. However simulations are time intensive due to complex three-dimensional meshing and computation time, limiting the number of geometric perturbations explored. A method is proposed in which the specific geometric features of this complex topography can be modified during a simulation thereby decreasing the time per geometric modification and removing the need for manual meshing of the complex structure. The surface of the seal whisker inspired geometry is parameterized into seven defining parameters, each of which is directly controlled in order to morph the surface into any realization within the defined parameter space. Once validated, the algorithm is used to explore the undulation amplitudes in the chord and thickness directions, by varying each independently from 0 to 0.3 thicknesses in increments of 0.05 at a Reynolds number of 500. The force and frequency response are examined for this matrix of geometric parameters, yielding detailed force trends not previously investigated. The impact of the bio-inspired morphing algorithm will allow for further optimization and development of force-mitigating underwater devices and other engineering applications in need of vibration suppression, frequency tuning, or force reduction.

Rub-impact dynamic analysis of a rotor with multiple wide-chord blades under the gyroscopic effect and geometric nonlinearity

In turbo-machinery, wide-chord blades are widely used due to the advantages of improving fan efficiency and aerodynamic performance. The rotor with multiple wide-chord blades is spaced from the outer casing. The small clearance may cause rub-impact fault between wide-chord blades and the casing, which induces different damage severity or the destruction of the whole machine. Numerical simulation is necessary to analyze this kind of rub-impact fault, but the solution process becomes complicated because of the coupling of geometric nonlinearity, local vibrations of wide-chord blades and gyroscopic motion of the rotor. This paper develops a rubbing rotor model with multiple wide-chord blades considering the gyroscopic effect and geometric nonlinearity induced by rub-impact. Based on the rub-impact model established for wide-chord blades, the high-order nonlinear governing equations of the bladed rotor are derived. Vibration responses are solved, and a series of dynamic characteristic analysis is carried out. The results reveal that high-order nonlinearity has a little effort on vibrations during slight rub-impact. But with the increase of transverse deformation induced by severe tip-rub, its influence cannot be ignored. Besides, localized rub-impact phenomenon of blades induced by external synchronous forces is found. Instead, external asynchronous force makes all blades rub, one after another along the circumferential direction of the disk, and there is a phase differenceΔφ=2π/Ω±ωNbbetween the vibration responses of adjacent blades. Then, we found that the swing motion intensifies the difference of transverse deformations along the chord direction of wide-chord blades with tip-rub, which may induce the edge failures. Also, the swing motion intensifies the steady rub-impact fault. It could weaken or eliminate its divergence and instability when the rotor with multiple wide-chord blades is unstable. The gyroscopic effect could weaken the swing motion, and then weakens the stable rub-impact fault.

Analysis of the Formation Mechanism and Evolution of the Perpendicular Cavitation Vortex of Tip Leakage Flow in an Axial-Flow Pump for Off-Design Conditions

To understand the formation mechanism and evolution process of the perpendicular cavitation vortex (PCV) of an axial flow pump for off-design conditions, turbulent cavitating flows were numerically investigated using the rotation curvature-corrected shear stress transport (SST-CC) turbulence model and the Zwart–Gerber–Belamri cavitation model. In this work, the origin and evolution of a PCV were analyzed through a high-speed photography experiment and numerical simulation. The results showed that the PCV came from a secondary tip leakage vortex (S-TLV) and was aggregated by the action of the re-entrant jet, combined with the cavitation bubbles driven by the radial flow to form the cavitation vortex (CV). With the joint action of leakage jet lifting and TLV entrainment, the PCV was reoriented and gradually became perpendicular to the chord direction. Then, the PCV and TLV collided, mixed, and entrained, which formed a strong pressure pulsation. The PCV was gradually divided into upper and lower parts. One part was combined with the residual part of the TLV and flowed to the next blade, and the other part flowed out of the impeller area along the axial direction. At the same time, the generation, evolution, and dissipation of the PCV formed high pulsation amplitudes and frequencies in the middle and rear above the blade suction.

Unsteady characteristics of pressure on wind turbine blade surface in the field

Field experiments are carried out to investigate the fluctuation characteristics of pressure on wind turbine blade surface in real operating environments. The tested wind turbine positioned pressure tapes along the blade span to obtain the dynamic pressure of seven airfoil sections over six rotation periods, and analyzed its time-domain, frequency domain, and standard deviation. The results show that the pressure on blade surface presents highly unsteady characteristics, and rotation of the wind turbine is one of the main factors that causes pressure fluctuations on the blade surface. The standard deviation of pressure near the leading edge of each airfoil section is relatively larger, indicating that the leading edge is the most sensitive to field wind conditions. Compared with the pressure surface, the blade suction surface contributes more to wind turbine power fluctuation and is more sensitive to various unsteady sources. Moreover, the standard deviation of the pressure on the blade pressure surface is largest at the tip, and the standard deviation of the pressure on the blade suction surface is clearly divided into two regions along the chord direction with different scales at different spanwise sections.

Evaluation of the Effects of Actuator Line Force Smearing on Wind Turbines Near-Wake Development

In the present study, the effects of the actuator line force smearing on the predicted near-wake development of a model wind turbine are evaluated. To exclude the uncertainties related to the blade loads computation, the loads of a corresponding blade-resolving simulation are imposed. Three force projection functions are applied, which all radially scale with the local chord length: an isotropic Gauss force distribution, an anisotropic Gauss distribution with distinct projection widths in the chord and thickness directions, and a Gauss-Gumbel projection function which creates an airfoil-like force distribution in the chord direction. Comparisons with corresponding blade-resolving simulations and experimental results show a good agreement of the tip vortex core size, position and circulation. Comparison of the mid-wake instantaneous streamwise velocity with blade-resolving simulations shows a thinner vortex sheet and stronger effects of the trailed vortices in the actuator line simulation. Although the bound vortex shape scales with the projection function, no significant difference was observed in the resulting tip vortices and near-wake flow field between the three projection functions used. It is attributed to the similar projection width in the tip vortex region for all cases considered. With the chosen grid refinement in the tip vortex area and a smearing width that scales with the chord length, tip vortices that compare with high-resolution experiments and high-fidelity blade-resolving simulation could be generated with the actuator line approach.

Computational analysis of NACA 0010 at moderate to high Reynolds number using 2D panel method

Wing structures as found in aircrafts and wind turbine blades are developed using airfoils. Computational methods are often used to predict the aerodynamic characteristics of such airfoils, typically the pressure, lift and drag force coefficients. In the present work, surface pressure coefficient distribution of NACA 0010 is evaluated using the 2D panel and Jukouwski methods for incompressible lifting flows for three Reynolds numbers, Re–3 x105, 5 x105, 1 x 106. The analysis was conducted for various AOA (angle of attack), between –20 to 100 for the airfoil with tripped and untripped conditions. The non–dimensional pressure coefficient along chord direction of airfoil is illustrated for upper and lower surfaces between –20 to 100 angle of attack. The coefficient of lift and drag as well as glide ratio are evaluated for all three Reynolds numbers. The present results from the 2D panel method are validated using the results from Hess and Smith, inverse design methods implemented on conformal mapped symmetric Jukouwski airfoil of 10% thickness to chord at 40 angle of attack.

Experimental determination of the dominant noise mechanism of rotating rotors using hot-wire anemometer

Aerodynamic noise restricts the development of wind turbines, however, the complex formation mechanism of aerodynamic noise needs to be explored for the successful realization of wind turbines in a wide range of applications. Herein, a two-dimensional hot-wire anemometer is used to capture the transient flow field at the rotor dominant sound source area from the open section of the wind tunnel. The influence of wind speed and tip speed ratio on velocity is systematically investigated by estimating the position and maximum value of velocity fluctuations. Moreover, the relationships between sound field and flow field are established in terms of frequency, position, and energy parameters. Finally, the noise generation mechanism is determined based on vortex and noise generation theories. The results reveal that the maximum velocity fluctuations are concentrated at 0.7–0.8C and 0.57–0.71 R in the chord and radial directions, respectively. One should note that the dominant sound source spectrum is consistent with the velocity fluctuation spectrum, exhibiting broadband characteristics. Furthermore, the sound source positions are consistent, but not coincident, with the positions of maximum velocity fluctuations. In addition, the sound source positions are closer to the blade tip and trailing edge in the radial and chord directions, respectively, than the maximum velocity fluctuation point. The deviations in radial and chord positions increase with increasing wind speed and tip speed ratio, whereas the deviations of maximum radial and chord position are found to be 1.4% and 36%, respectively. The sound pressure level and velocity fluctuation exhibit excellent consistency under different working conditions, such as different wind speeds and tip speed ratios. It can be concluded that the dominant noise is a broadband noise due to pressure fluctuations, which are induced by the interactions between turbulent flow and trailing edge. These results provide a baseline for the design and development of optimal blades and noise reduction.