Angle Of Pitch Research Articles

Trailing-edge boundary layer characteristics of a pitching airfoil at a low Reynolds number

The periodic variation of the flow pattern and the boundary layer characteristics near the trailing edge of a pitching NACA (National Advisory Committee for Aeronautics) 0012 airfoil are examined experimentally in this study. The mean pitching angle and pitching amplitude were 0° and 7.5°, respectively, and the reduced frequency varied from 0.094 to 0.157. Static cases with various angles of attack were tested for reference. All the tests were conducted at a low Reynolds number of 66000. Particle image velocimetry was used as the primary measurement for flow visualization and boundary layer analysis. The periodic development of the flow pattern close to the trailing edge within one pitching cycle was monitored. The instantaneous flow patterns acquired at certain phase angles are compared with the static cases, demonstrating the influences of the pitching motion, including the lag effect on the boundary layer. A vortex street is observed as the airfoil achieves certain pitching angles, leading to the largest boundary layer displacement thickness at the corresponding side. As the pitching angle increases, transition of the boundary layer at the trailing edge occurs at a higher incidence compared with the static cases. Increasing the pitching frequency would lead to the decrease in the vortex structure strength and delayed boundary layer transition near the trailing edge.

The Importance of Flapping Kinematic Parameters in the Facilitation of the Different Flight Modes of Dragonflies

To better understand dragonflies’ remarkable flapping wing aerodynamic performance, we measured the kinematic parameters of the wings in two different flight modes (Normal Flight Mode (NFM) and Escape Flight Mode (EFM)). When the specimens switched from normal to escape mode the flapping frequency was invariant, but the stroke plane of the wings was more horizontally inclined. The flapping of both wings was adjusted to be more ventral with a change of the pitching angle that resulted in a larger angle of attack during downstroke and smaller during upstroke to affect the flow directions and the added mass effect. Noticeably, the phasing between the fore and hind pair of wings varies between two flight modes, which affects the wing-wing interaction as well as body oscillations. It is found that the momentum stream in the wake of EFM is qualitatively different from that in NFM. The change of the stroke plane angle and the varied pitching angle of the wings diverts the momentum downwards, while the smaller flapping amplitude and less phase difference between the wings compresses the momentum stream. It seems that in order to achieve greater flight maneuverability a flight vehicle needs to actively control positional angle as well as the pitching angle of the flapping wings.

Research on the key technology of narrow split crawler drilling rig

According to the complex construction conditions in China, such as coal mines roadway cross section is small and the space is little, a new type of down hole drill was designed in this paper. In order to improve the mobility under the coal mines, the split type and narrow body structure was adopted in the design drill process, the compact type and more range combined frame with the ability which can construct for more rows level drill holes in the coal roadways and all–round pitching angle drilling in the rock. The industrial test showed that the new type drilling has well application effect in complex conditions with flexible mobility and process adaptability under the coal mines, the workers labor intensity was obviously reduced.

Numerical study on the hydrodynamic performance of a semi-passive oscillating hydrofoil

The bio-inspired oscillating hydrofoils are capable of harvesting energy from tidal currents. In this study, the effects of mechanical (spring and damping coefficients) and kinematic (pitching amplitude and oscillation frequency) parameters on the performance of the semi-passive oscillating hydrofoil (NACA 0015) system were numerically studied at a high Reynolds number of 106. It is found that the spring (k *) is necessary to obtain a stable heaving response. The initial pitching angle has a significant effect on the heaving response, while it has a little impact on the power output. The balance position of the heaving response deviates notably from the initial position, especially when the initial pitching angle is zero. A larger damping coefficient (c *) results in poor energy harvesting performance due to a smaller oscillation amplitude. The heaving amplitude increases firstly and decreases afterward with the increase of the pitching amplitude (θ0), while it decreases monotonically with increasing oscillation frequency (f *). When f *>0.15, the heaving and pitching power coefficients increase and decrease with increasing f *, respectively. The net power coefficient decreases at high oscillation frequencies because the increase in the heaving power coefficient is smaller than the decrease in the pitching power coefficient. When k* = 0.5 and c* = 0.8π, an optimal energy harvesting efficiency of 40.84% is achieved at θ0=85° and f * = 0.125.

On calculation of the pitch and angle of pitch of a closed ruled surface of dimension (k + 1) using a rotation minimizing frame in Euclidean space ℝn

In this paper, first, the pitch and the angle of pitch of a closed ruled surface of dimension (k + 1) are calculated according to a rotation minimizing frame in Euclidean space . To calculate this pitch and this angle of pitch of the closed ruled surface of dimension (k + 1), three different ruled surfaces are taken according to the rotation minimizing frame. Therefore, for these three different ruled surfaces, three different situations are found. Second, by taking any curve in four‐dimensional Euclidean space, the closed ruled surface of this curve, its orthogonal trajectory, the pitch, and the angle of pitch of this closed ruled surface are obtained according to the rotation minimizing frame. Finally, the pitch and the angle of pitch of the closed ruled surface of dimension (k + 1) are generalized to n‐dimensional Euclidean space with the help of the rotation minimizing frame.

Numerical investigation of dynamic stall reduction on helicopter blade section in forward flight by an airfoil deformation method

In the present work, airflow over blade section of helicopter rotor in forward flight is investigated numerically to offer a proposal for reduction or alleviation of dynamic stall on retreating blade. Unsteady 2-D compressible Reynolds-averaged Navier–Stokes equations are solved at flow conditions experienced by retreating blade of UH-60A helicopter rotor. For validation and verification purposes, flows around static and pitching airfoils in constant and variable flow Mach numbers are simulated and compared with other numerical results and experimental data. Having defined two deformation parameters, nine different permanently-deformed airfoils are produced from SSC-A09 airfoil. Flow field around these nine airfoils are simulated in variable flow Mach number with defined pitching angles. Coefficients of $$C_{{\text{l}}}$$ , $$C_{{\text{d}}}$$ and $$C_{{\text{m}}}$$ of these deformed SSC-A09 airfoils are compared with those of original airfoil to demonstrate that airfoil deformation proposed here is able to reduce and alleviate dynamic stall. Quantitatively, $$C_{{{\text{d}},\max }}$$ and absolute value of $$C_{{{\text{m}},\min }}$$ have been reduced up to 49.2% and 25%, respectively. In addition it is worth to mention that in some flow conditions dynamic stall is even eliminated with the proposed airfoil deformation. These are all achieved by permanent airfoil deformation which does not impose design complexities and expenses needed by dynamic airfoil deformation as proposed by others.

Load cell-based PID method controlled Segway system modelling and simulation

In the present study, mathematical modelling and simulation of load cell-based Segway has been done. Four load cells placed on the Segway to provide the control of the system. According to the measured weight information, the dynamic model of the system can be updated instantly. This operation makes the Segway control easier by changing the maximum pitch angle. In order for the system to stay in balance on two wheels, it must move at the appropriate pitching angle and at the desired speed. The control of the suitable pitching angle and speed are controlled by the PID method. As a result of the simulation in Matlab/Simulink environment, Segway's speed information, current information of BLDC and pitching angle can be accessed. As a result of the study, it is thought that the load cell-based Segway can be controlled more effectively.

The Influence of Hydrodynamic Changes in a System with a Pitched Blade Turbine on Mixing Power

This paper presents an analysis of hydrodynamics in a tank with a 45° and 60° pitched blade turbine impeller operating while emptying the mixer and with an axial agitator working during axial pumping-down of water at different water levels above the impeller. Measurements made with the PIV method confirmed the change in direction of pumping liquid after the level dropped below the critical value, with an almost unchanged liquid stream flowing through the mixer. It was found that an increase in the value of the tangential velocity in the area of the impeller took place and the quantity of this increase depended on the angle of the blade pitch and the rotational frequency of the impeller. Change in this velocity component increased the mixing power.

Attitude control strategy of airship based on active disturbance rejection controller

The flight performance of the airship is closely related to the attitude control. For the stability of the station-keeping and the rapidity and accuracy of the trajectory tracking, it is necessary to study the attitude control of the airship. This paper proposes a strategy including two parties. First, a novel control mechanism combining moving-mass and tail vector thrust is proposed, and the airship mathematical model is introduced briefly. Second, active disturbance rejection controller (ADRC) is introduced which is developed from classical proportion–integration–differentiation (PID) controller. Considering the special working environment of stratospheric airship, the wind field is added to the simulation as external disturbance. The results show that the system is stable which can track any expected angle of pitch and yaw directions with small overshoot and rise time. In general, with or without the disturbance of 4 m/s wind field, the ADRC performs better than PID controller.

Rotation improvement of vertical axis wind turbine by offsetting pitching angles and changing blade numbers

To improve the power extraction performance and self-starting characteristics of the vertical axis wind turbine (VAWT), the effect of offsetting pitching angles and blade numbers on the performance of a wind-induced rotation VAWT has been systematically investigated. Different from the conventional numerical and experimental approach, the rotation velocity of the turbine is driven by the aerodynamic torque of the blade in the present study. The flow around the turbine was simulated using Fluent 6.3 code, and the governing equation of the turbine’s rotation was coupled to the code through UDF. The optimized pitching angle β was found to be of −4°, at which the maximum 5.89 and 5.14 times average power increasing were achieved for the turbine with 5-blades and 3-blades, respectively. Moreover, shorter self-starting time was also observed for the turbine with β = −4° at larger wind velocity (>9 m/s). In addition, the influence of the blade number on the performance of the turbine depended on the wind velocity. The analysis of the flow field of the turbine showed that the offsetting pitching angle and blade number could suppress or delay the vortex separation, and therefore improve the overall performance of the turbine.

The Influence of Winglet Pitching on the Performance of a Model Wind Turbine: Aerodynamic Loads, Rotating Speed, and Wake Statistics

The objective of this study is to investigate the influence of winglet pitching as an aero-brake on the performance of a model wind turbine by wind tunnel experiments. Time-resolved particle image velocimetry, force sensor, and datalogger were used to characterize the coupling between wake statistics, aerodynamic loads, and rotation speed. Results highlighted that, for a winglet with 4% of the rotor diameter length, the increase of its pitching angle can significantly reduce the turbine rotation speed up to ∼28% and thrust coefficient of ∼20%. The winglet pitching induced minor influence on the velocity deficit in the very near wake regions, while its influence on accelerating the wake recovery become clear around three diameters downstream the turbine rotor. The turbulence kinetic energy exhibited a distinctive increase under large pitching angles in the near wake region at the turbine hub height due to the strong vertical flow fluctuations. Further investigation on the spectra of wake velocities revealed that the pitching of winglet can suppress the high-pass filtering effects of turbines on wake fluctuations; such large-scale turbulence facilitated the flow mixing and accelerated the wake transport.

Effects of Euler Angles of Vertical Cambered Otter Board on Hydrodynamics Based on Response Surface Methodology and Multi-Objective Genetic Algorithm

Abstract In this present work, effects of three Euler angles (angle of attack (AOA), angle of trim (AOT), and angle of pitch (AOP)) of vertical cambered otter board on hydrodynamic characteristics (drag coefficient (Cd), lift coefficient (Cl), center-of-pressure coefficients (Cp)) were studied based on numerical simulation combined with Kriging response surface methodology (KRSM) and multi-objective genetic algorithm (MOGA). Wind tunnel experiments were carried out to validate the accuracy of the response surface based on numerical simulation. It was demonstrated that AOA had noticeable effects on Cd and Cl, while AOT and AOP had fewer effects. The working posture of the otter board was recommended to lean inward (0 deg–6 deg) and forward (−10 deg–0 deg) to improve the lift-drag ratio without sacrificing Cl. The influences of AOT and AOP on positions of center-of-pressure points were less significant than that of AOA and decreasing with the increase of AOA. Besides, the response surface of hydrodynamic coefficients around the critical AOA was a decent indicator of the occurrence of stall. Finally, three candidate cases were selected to satisfy the high working efficiency by MOGA, which was consistent with the above recommendations. This study provided a scientific reference of response surface experimental investigations methodology in the fishery engineering and the configuration of Euler angles of otter board.

Effect of Initial Pitching Angle on Helicopter Ditching Characteristics Using Smoothed-Particle-Hydrodynamics Method

The present Paper investigates the ditching characteristics of a helicopter model by means of an in-house-developed smoothed-particle-hydrodynamics solver coupled with a six degree-of-freedom motion equation. Verification and validation have confirmed the feasibility and accuracy of the developed solver in predicting hydrodynamic problems. In view of the inherent importance, the effect of initial pitching angle of helicopter was comprehensively considered. Numerical results show that the helicopter experiences a subsequent nose-up and nosedown motion for all the positive initial pitching angles during ditching which is caused by the hydrodynamic overpressure and suction effects. The initial pitching angle significantly affects the helicopter ditching characteristics in terms of load and pressure distribution. For the specific configuration of the helicopter, ditching with initial pitching angle at 6 or 8 deg endures relative lower hydrodynamic load in both horizontal and vertical directions, which can be regarded as preferable setups for a controllable ditching event.

Dynamic Scattering Approach for Solving the Radar Cross-Section of the Warship under Complex Motion Conditions

To obtain the electromagnetic scattering characteristics of the warship under complex motion conditions, a dynamic scattering approach (DSA) based on physical optics and physical theory of diffraction is presented. The observation angles, turret rotation, hull attitude changes and sea wave models are carefully studied and discussed. The research results show that the pitching and rolling angles have a large effect on the radar cross-section (RCS) of the warship. Turret movement has a greater impact on its own RCS but less impact on the warship. The RCS of the warship varies greatly at various azimuths and elevations. Different sea surface models have a greater impact on the lateral RCS of the warship. The DSA is effective and efficient to study the dynamic RCS of the warship under complex motion conditions.

On the Performance of Swing Arm Flapping Turbines

Abstract This study investigates the energy extraction mechanism by means of swing arm turbine. The swing arm turbines have a particular motion pattern. The pure translation motion in the conventional flapping turbine changes based on the swing arm rotation. The laminar flow around a NACA0015 is resolved using computational fluid dynamics (CFD) method. The turbine blades are equipped with an oscillating gurney flap for trying to boost the system efficiency. The connected gurney flap oscillates with a given pitching angle. A user-defined function and the sliding dynamic mesh technique available in ansys fluent version 15 are used to adjust both the blade and the flap positions during the turbine flapping cycle. The effects of the swing factor and the flap length on the system performance are provided. It is shown that the suggested strategy of control is able to alter the pressure distribution during both the up stroke and down stroke phases, which changes the blade aerodynamic forces during all the flapping cycle portions and therefore improving the turbine efficiency.

Computational Model for Simulation of Lifeboat Free-Fall during Its Launching from Ship in Rough Seas

In order to improve the accuracy of the freefall of lifeboat motion simulation in a ship life-saving simulation training system, a mathematical model using the strip theory and Kane’s method is established for the freefall of the lifeboat into the water from a ship. With the boat moving on a skid, the model of the ship’s maneuvering mathematical group (MMG) is used to model the motion of the ship in the waves. Based on the formula of elasticity and friction theory, the forces of the skid acting on the boat are calculated. When the boat enters the water, according to the analytical solution theory of slamming, the slamming force of water entry is solved. The simulation experiments are carried out by the established model. The results of the numerical simulation are compared with the calculation results of the hydrodynamics software Star CCM+ at water entry under initial condition A in the paper. The position and velocity of the center of gravity of the boat, the angle, and velocity and acceleration of pitch calculated by the two methods are in good agreement. There is a little difference between the values of translation acceleration calculated by the two methods, which is acceptable. This shows that our numerical algorithm has good accuracy. A qualitative analysis is performed to find the safe point of water entry under the condition of different wave heights and two situations of a ship encountering waves. Finally, the model is applied to the ship life-saving training system. The model can meet the system requirements and improve the accuracy of the simulation.

Ride comfort performance of hydro pneumatic isolation for soil compactors cab in low frequency region

The hydro pneumatic isolation (HPI) of the cab combined by the high static stiffness and nonlinear viscous damping of the pneumatic isolation; and nonlinear adjustable damping of the hydraulic isolation are proposed. Based on the simulation and experimental studies, a nonlinear dynamic model of the soil compactor interacting with the deformable terrains is built to analyze the low frequency ride comfort of the HPI. The HPI’s performance for improving the ride comfort and health of the driver is evaluated via both the power-spectral-density and root-mean-square of acceleration responses of the driver’s seat heave, pitching and rolling cab angles. The research results show that the HPI’s characteristics with high static stiffness and nonlinear damping have an obvious impact on reducing low frequency vibration and controlling the cab shake of the vehicle in comparison with the traditional rubber mounts.

Control performance of suspension system of cars with PID control based on 3D dynamic model

To evaluate the control performance of the PID controller for the cars, a 3D car dynamic model with 8-DOF which can fully reflect the pitch and roll of the car body is proposed in this study. The PID controller is then researched and applied to control the active suspension system of the cars under the different excitations of the road surface and the various car speeds. The control performance for improving the ride comfort of the driver is evaluated via the root-mean-square (RMS) of acceleration responses of the vertical driver’s seat, pitching and rolling car body angles. The research results show that the PID controller for the car suspension system have an obvious impact on reducing the vibration and controlling the car body shaking in comparison with the passive suspension system.

Design improvement of flapping hydrokinetic turbines

This investigation deals with the flow control and the enhancement of the output power of a flapping foil turbine. The connected gurney flap (GF) is a small arc that oscillates with a given pitching angle. The incompressible laminar flow around a simple flat plate equipped with an oscillating gurney flap is solved using a computational method. A user-defined function and a coupled layering/sliding dynamic mesh technique available in ANSYS FLUENT.15 are used to adjust both the blade and the flap positions during the turbine flapping cycle. It was shown that an appropriate synchronization between the flap oscillation and the turbine blade rotation could modify the blade flap camber, which corrects, in turn, the pressure distribution and therefore boosts the lift force during both the up-stroke and down-stroke stages. The application of this strategy of control enhances the output power dramatically compared with a clean flapping turbine blade.

Numerical parametric study on three-dimensional rectangular counter-flow thrust vectoring control

Recently, fluidic thrust vectoring control is popular for micro space launcher propulsion systems due to its several advantages, such as fast dynamic responsiveness, better control effectiveness, and no moving mechanical equipment. Counter-flow thrust vectoring control is an especially effective technique by utilizing less suction flow to control the mainstream deflection flexibly. In the current work, theoretical and numerical analyses are performed together to elaborate on the performance of the three-dimensional rectangular counter-flow thrust vectoring control system. A new propulsion nozzle of Mach 2.5 is devised by method of characteristics. To testify the feasibility and accuracy of the present research methodology, numerical results were validated against experimental data from the open literature. The computational result using the standard k-epsilon turbulence model reveals a good match with experimentally measured static pressure values along the centerline of the upper suction collar. The influence of several key parameters on vectoring performance is investigated herein, including the mainstream temperature, collar radius, horizontal collar length, and gap height. Critical parameters have been quantitatively analyzed, such as static pressure distribution along the centerline of the upper suction collar, pitching angle, suction mass flow ratio, and thrust coefficient. Furthermore, the flow-field features are qualitatively expounded based on the static pressure contour, streamline, iso-turbulent kinetic energy contour, and iso-Mach number contour. Some important conclusions are offered for further studies. The mainstream temperature mainly affects different dynamic characteristics of the mixing shear layer, including the convective Mach number of the shear layer, density ratio, and flow velocity ratio. The collar radius influences the pressure gradient near the suction collar surface significantly. The pitching angle increases rapidly with the increasing collar radius. As the horizontal collar length increases, the systematic deflection angle initially increases then decreases. The highest pitching angle is obtained for L/ H = 3.53. With regard to the gap height, a larger gap height can achieve a higher pitching angle.