Wind Tunnel Measurements of Flow-Induced Vibration of a NACA0015 Airfoil Model

2014 ◽  
Author(s):  
Petr Šidlof ◽  
Václav Vlček ◽  
Martin Štěpán ◽  
Jaromír Horáček ◽  
Martin Luxa ◽  
...  
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Aerodynamic Force ◽  
Dynamic Pressure ◽  
Mechanical Vibration ◽  
Vertical Position ◽  
High Speed Camera ◽  
Flow Induced Vibration ◽  
Aeroelastic System ◽  
Stiffness Matrices

The paper reports on interferometric measurements of flow over a NACA0015 airfoil model during flutter limit cycle oscillations. The airfoil model is fixed on an elastic support allowing motion with two degrees of freedom — pitch and plunge. The structural mass and stiffness matrices can be tuned to certain extent, so that the eigenfrequencies of the two modes approach as needed. The model is equipped with dynamic pressure probes and sensors measuring the airfoil vertical position. The flow field around the airfoil was measured by Mach-Zehnder interferometer and registered using a high-speed camera synchronously with the mechanical vibration and pressure measurements. The Mach number of the incident airflow was gradually increased and the response of the aeroelastic system to initial impulse measured, until the flutter instability onset occurred. Flutter boundaries were evaluated for various additional masses attached (i.e., for various plunging mode eigenfrequencies), and post-critical behavior of the system investigated. The interferograms recorded by the high-speed camera were postprocessed, yielding pressure distribution around the airfoil during its vibration and an estimate of the total aerodynamic force and energy transfer from the airflow to the structure.

Numerical study on the mechanism of drag reduction for interceptors on planning boats

2021 ◽  
Author(s):  
Lianzheng Cui ◽  
Zuogang Chen ◽  
Yukun Feng
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Numerical Study ◽  
Dynamic Pressure ◽  
Motion Model ◽  
Gauge Pressure ◽  
Reduction Effect ◽  
Pressure Resistance ◽  
Viscous Pressure

The drag reduction effect of interceptors on planning boats has been widely proven, but the mechanism of the effect has been rarely studied in terms of drag components, especially for spray resistance. The resistance was caused by the high gauge pressure under the boats transformed from the dynamic pressure, and it is the largest drag component in the high-speed planning mode. In this study, numerical simulations of viscous flow fields around a planning boat with and without interceptors were conducted. A two degrees of freedom motion model was employed to simulate the trim and sinkage. The numerical results were validated against the experimental data. The flow details with and without the interceptor were visualized and compared to reveal the underlying physics. A thinner and longer waterline could be achieved by the interceptor, which made the boat push the water away more gradually, and hence, the wave-making resistance could be decreased. The improved waterline also reduced the component of the freestream normal to the hull surface and led to the less transformed dynamic pressure, resulting in the lowAer spray resistance. Furthermore, the suppression of the flow separation could also be benefited from the interceptor; the viscous pressure resistance was therefore decreased.

Influence of Bistable Plunge Stiffness On Nonlinear Airfoil Flutter

2021 ◽  
Author(s):  
Renan F. Corrêa ◽  
Flávio D. Marques
Keyword(s):  
Degrees Of Freedom ◽  
Initial Conditions ◽  
Equations Of Motion ◽  
Mechanical Vibration ◽  
Nonlinear Behavior ◽  
Limit Cycle Oscillation ◽  
Restoring Force ◽  
Aeroelastic System ◽  
Technical Literature ◽  
Practical Applications

Abstract Aeroelastic systems have nonlinearities that provide a wide variety of complex dynamic behaviors. Nonlinear effects can be avoided in practical applications, as in instability suppression or desired, for instance, in the energy harvesting design. In the technical literature, there are surveys on nonlinear aeroelastic systems and the different manners they manifest. More recently, the bistable spring effect has been studied as an acceptable nonlinear behavior applied to mechanical vibration problems. The application of the bistable spring effect to aeroelastic problems is still not explored thoroughly. This paper contributes to analyzing the nonlinear dynamics of a typical airfoil section mounted on bistable spring support at plunging motion. The equations of motion are based on the typical aeroelastic section model with three degrees-of-freedom. Moreover, a hardening nonlinearity in pitch is also considered. A preliminary analysis of the bistable spring geometry’s influence in its restoring force and the elastic potential energy is performed. The response of the system is investigated for a set of geometrical configurations. It is possible to identify post-flutter motion regions, the so-called intrawell, and interwell. Results reveal that the transition between intrawell to interwell regions occurs smoothly, depending on the initial conditions. The bistable effect on the aeroelastic system can be advantageous in energy extraction problems due to the jump in oscillation amplitudes. Furthermore, the hardening effect in pitching motion reduces the limit cycle oscillation amplitudes and also delays the occurrence of the snap-through.

Dynamic and Compliant Characteristics of a Cartesian-Guided Tripod Machine

2004 ◽  
Vol 128 (2) ◽  
pp. 494-502 ◽  
Author(s):  
Jeng-Shyong Chen ◽  
Wei-Yao Hsu
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Mechanical Vibration ◽  
Maximum Amplitude ◽  
High Gain ◽  
Velocity Change ◽  
Flexible Mode ◽  
Look Ahead ◽  
High Acceleration ◽  
Acceleration And Deceleration

This paper is focused on the dynamic and compliant characteristics of a three-axis parallel kinematic machine called a Cartesian-guided tripod (CGT), which has a passive leg locking the platform three rotational degrees of freedom. Because no constraint mechanism is perfect with infinite rigidity, a compliance model has been developed to determine the maximum amplitude of the passive-leg parasitic motions using given loads. System compliance, dynamic characteristics, vibration modes, and servo-contouring errors of the CGT driving system have also been evaluated under high-speed machining conditions. The nonlinear dynamic effects, such as inertia and gravity, can be controlled within acceptable accuracy using the high-gain servo-feedback control techniques. The CGT dominant flexible mode occurs on the horizontal platform-leg vibration. The platform-leg flexible mode can produce significant jerk-induced mechanical vibration on the platform when a sudden velocity change is commanded. Look-ahead Cartesian-based path acceleration and deceleration control was found to be an efficient tool to reduce the jerk-induced mechanical vibration, although the CGT was drive controlled at the joint level. It was found that at high acceleration application, such as high-speed mold and die machining, the elastic elongation of the driving leg caused by the high acceleration force became the dominant contouring error sources.

Study on the Characteristics of Contact Line and Liquid Film in Rectangular Microgrooves Under Vibration Conditions

2011 ◽  
Author(s):  
Wei Cao ◽  
Xuegong Hu ◽  
Chaohong Guo ◽  
Dawei Tang
Keyword(s):  
Liquid Film ◽  
Contact Line ◽  
Heat Input ◽  
High Speed ◽  
Mechanical Vibration ◽  
Line Length ◽  
Oscillation Period ◽  
Wide Field ◽  
High Speed Camera ◽  
Phase Contact

With the help of a high-speed camera (30000 Frames/second) and a wide-field stereo-microscope, the effects of mechanical vibration on the meniscus film and triple-phase contact line in rectangular microgrooves were experimentally investigated. Distilled water was used as working liquid. The images of the oscillated meniscus film in an oscillation period were captured through the high speed camera and they were analyzed using a MATLAB program. The results show that as the vibration table moves upward, the length of contact line increases; as the vibration table moves downward, the length of contact-line decreases. During the oscillation, the axial liquid film spreads upward further along the microgrooves and the deformation of the contact line becomes more obvious. The increase of the triple-phase contact line length caused by the external mechanical vibration is helpful for contact line heat transfer enhancement. Besides, deformation curve of the contact line with and without heat input under different vibration conditions is similar, while the contact line with heat input is shorter.

Interval Analysis-Based Flutter Analysis of Airplane Wings

2012 ◽  
Author(s):  
Singiresu S. Rao ◽  
Luna Majumder
Keyword(s):  
High Speed ◽  
Aerodynamic Force ◽  
Reduction Process ◽  
Probabilistic Information ◽  
Natural Modes ◽  
Stiffness Matrices ◽  
Flutter Analysis ◽  
Improved Performance ◽  
Equivalent Reduction ◽  
Structural Mode

Modern aircrafts require improved performance and maneuverability while they conduct the missions. The flutter, an aeroelastic phenomenon is one of the important situations that limit the aircraft speed. Furthermore, for aircraft operated at high speed, many uncertainties may exist in its structural and aerodynamics characteristics. Especially, a slight change in the wing structural mode may induce a variation in its aerodynamic force distribution. In this work, an interval-based approach is used to handle the uncertainties associated with the flutter analysis. The set-theoretic representation of uncertainty is motivated by a possible lack of detailed probabilistic information on the distributions of the parameters. The analysis procedure is performed on an aircraft wing structure using finite element idealization and the results have shown the effectiveness and feasibility of the interval method. The order of the aerodynamic, mass and stiffness matrices of the assembled structures is reduced by introducing the first few natural modes of the structure as generalized coordinates. System equivalent reduction expansion process is used for model reduction which uses the generalized inverse and carries information pertaining to the selected modes at the selected set of degrees of freedoms. The system equivalent reduction formulation allows the reduction process to preserve the dynamics of the full system in a reduced set of matrices. Thus the order of the eigenvalue problem in the flutter analysis is reduced to one-third of the corresponding statics problem.

scholarly journals Analysis of a piecewise linear aeroelastic system with and without tuned vibration absorber

2020 ◽  
Author(s):  
János Lelkes ◽  
Tamás Kalmár-Nagy
Keyword(s):  
Wind Speed ◽  
Degrees Of Freedom ◽  
Aerodynamic Force ◽  
Piecewise Linear ◽  
Piecewise Linear Approximation ◽  
Vibration Absorber ◽  
Aeroelastic System ◽  
Stall Flutter ◽  
The Stability ◽  
Tuned Vibration Absorber

Abstract The dynamics of a two-degrees-of-freedom (pitch–plunge) aeroelastic system is investigated. The aerodynamic force is modeled as a piecewise linear function of the effective angle of attack. Conditions for admissible (existing) and virtual equilibria are determined. The stability and bifurcations of equilibria are analyzed. We find saddle-node, border collision and rapid bifurcations. The analysis shows that the pitch–plunge model with a simple piecewise linear approximation of the aerodynamic force can reproduce the transition from divergence to the complex aeroelastic phenomenon of stall flutter. A linear tuned vibration absorber is applied to increase stall flutter wind speed and eliminate limit cycle oscillations. The effect of the absorber parameters on the stability of equilibria is investigated using the Liénard–Chipart criterion. We find that with the vibration absorber the onset of the rapid bifurcation can be shifted to higher wind speed or the oscillations can be eliminated altogether.

scholarly journals Recent advances in nano-opto-electro-mechanical systems

Nanophotonics ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Nan Xu ◽  
Ze-Di Cheng ◽  
Jin-Dao Tang ◽  
Xiao-Min Lv ◽  
Tong Li ◽  
...  
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
High Efficiency ◽  
Quantum Information Processing ◽  
Mechanical Vibration ◽  
Mechanical Systems ◽  
Multiple Quantum ◽  
Vibration Modes ◽  
Recent Developments ◽  
On Chip

Abstract Nano-opto-electro-mechanical systems (NOEMS), considered as new platforms to study electronic and mechanical freedoms in the field of nanophotonics, have gained rapid progress in recent years. NOEMS offer exciting opportunities to manipulate information carriers using optical, electrical, and mechanical degrees of freedom, where the flow of light, dynamics of electrons, and mechanical vibration modes can be explored in both classical and quantum domains. By exploiting NOEMS concepts and technologies, high speed and low-power consumption switches, high-efficiency microwave-optical conversion devices, and multiple quantum information processing functions can be implemented through on-chip integration. This review will introduce the principles of NOEMS, summarize the recent developments, and important achievements, and give a prospect for the further applications and developments in this field.

scholarly journals Aerodynamics of inclined cylindrical bodies free-flying in a hypersonic flowfield

2021 ◽  
Vol 62 (9) ◽  
Author(s):  
Patrick M. Seltner ◽  
Sebastian Willems ◽  
Ali Gülhan ◽  
Eric C. Stern ◽  
Joseph M. Brock ◽  
...  
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Numerical Data ◽  
Static Stability ◽  
Free Flight ◽  
Aerodynamic Coefficients ◽  
Flow Topology ◽  
Motion Data ◽  
Continuous Rotation ◽  
German Aerospace

Abstract The influence of the flight attitude on aerodynamic coefficients and static stability of cylindrical bodies in hypersonic flows is of interest in understanding the re/entry of space debris, meteoroid fragments, launch-vehicle stages and other rotating objects. Experiments were therefore carried out in the hypersonic wind tunnel H2K at the German Aerospace Center (DLR) in Cologne. A free-flight technique was employed in H2K, which enables a continuous rotation of the cylinder without any sting interferences in a broad angular range from 0$$^{\circ }$$ ∘ to 90$$^{\circ }$$ ∘ . A high-speed stereo-tracking technique measured the model motion during free-flight and high-speed schlieren provided documentation of the flow topology. Aerodynamic coefficients were determined in careful post-processing, based on the measured 6-degrees-of-freedom (6DoF) motion data. Numerical simulations by NASA’s flow solvers Cart3D and US3D were performed for comparison purposes. As a result, the experimental and numerical data show a good agreement. The inclination of the cylinder strongly effects both the flowfield and aerodynamic loads. Experiments and simulations with concave cylinders showed marked difference in aerodynamic behavior due to the presence of a shock–shock interaction (SSI) near the middle of the model. Graphic abstract

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