Vibration Phase Angle Research Articles

Enhanced interfacial boiling of impacting droplets upon vibratory surfaces

HypothesisDespite the flourishing studies of droplet interfacial boiling, the boiling upon vibratory surfaces, which may cause vigorous liquid–vapor-solid interactions, has rarely been investigated. Enhanced boiling normally can be gained from rapid removal of vapor and disturbance of liquid–vapor interface. We hypothesize that the vibratory surfaces enhance both effects with new intriguing phenomena and thus, attain an enhanced boiling heat transfer. ExperimentsWe experimentally investigated the impacting fluid dynamics and coupled heat transfer patterns of multiple droplets and a single droplet impinging on still and vibratory surfaces of various materials and different wettability. FindingsThe boiling under vibratory surfaces with increased vibration velocity amplitude and enhanced wettability can be enhanced by 80% in heat transfer coefficient and Nusselt number, which is attributed to several reasons: shortened bubble lifespan, thinner and smaller bubbles, and enhanced disturbances in liquid–vapor interfaces. The vibration also delays the Leidenfrost point when the droplet impacts a descending surface, which shows that the droplet impact moment (vibration phase angle) is particularly crucial. The descending surface releases the generated vapor actively and facilitates liquid–solid contact, thereby delaying the Leidenfrost. From fundamentals to application, this article strengthens our understanding of vibrated interfacial boiling in scenarios closer to multiple natural processes and practical industries.

A Prediction Method with Altering Equivalent Stiffness for Damping Evaluation of Shrouded Bladed Disk Dynamic Systems

In turbomachinery bladed disks are typical cyclic symmetric structures where high-cycle fatigue of the blades can easily occur. Increasing the shroud structure is an effective blade vibration reduction method using the dry friction of the shroud contact surface to dissipate vibration energy. During one vibration cycle of the blade, the contact surface of the shroud may have one or several states of stick, slip, and separation due to the different amplitude of blade, which affects not only the damping, but also the stiffness of the system. This paper proposes a method to analyze the damping characteristics of blades with shroud considering the change of equivalent contact stiffness of the shroud by using the finite element method. With a 2D contact model, this method calculates the equivalent damping and obtains the damping characteristic curve to evaluate the damping of shroud. During the design phase, the objective is that when resonance occurs, the shroud can provide the optimal damping ratio under the allowable vibration stress of the blade. The parameter sensitivity of the damping characteristic for one bladed disk with parallel shroud is investigated. It is shown that vibration phase angle, contact stiffness, contact force, friction coefficient significantly influence the damping characteristics.

A new rotor balancing method using amplitude subtraction and its performance analysis with phase angle measurement-based rotor balancing method

In order to balance a rotor, the standard rotor balancing methods involve measurement of vibration amplitude and vibration phase angle. But accurate phase angle measurement is generally difficult because vibration phase is sensitive to speed variations and it is difficult to maintain a constant speed in operating condition. Also, phase angle measurement requires very high end instrumentation for accurate phase angle measurement. Number of trial runs during balancing process also plays an important criterion in deciding the effectiveness of that method. A Method is considered to be more effective if it balances a rotor in less number of trial runs. This paper presents a novel rotor balancing method called amplitude subtraction method in which vibration amplitudes are measured only. Performance of this method is analysed by a comparative study with phase angle based rotor balancing method (trim balancing method). Trim balancing and amplitude subtraction method are compared on the basis of its accuracy and number of trial runs during balancing process. The results of experimentation demonstrate successful implementation of proposed method.

육상에 설치된 저속 7실린더 디젤엔진의 폭발 기진력 및 고진동 현상

A 7K60MC-S low speed diesel engine in a power plant has frequently experienced high vibration since the unit completed construction works. Up to date, no fundamental vibration solutions were reached. Hence, several vibration tests and analyses were conducted to identify the root cause of this high vibration and to suggest the optimal countermeasures for diesel engine. The 9.25 Hz and 25.4 Hz vibrations have been observed on main body during operation. The magnitude of engine upper structural vibration is generally similar in horizontal transverse direction. However, differences in the 'Fore' and 'After' vibration magnitude with the same vibration phase angle at 9.25 Hz occur due to the explosion pulsations of 7 cylinders and the Inertia momentum added by the SCR (selective catalytic reduction) duct system. It was analyzed that the excess structural vibration occurred when the natural frequency of engine body is affected by the exciting sources due to the explosion pressure and the discharge pulsation of the seven cylinders in resonance range.

The Flexure-Torsion Flutter of Aerofoils in Cascade : 1st Report, Computation and Experiment of Unsteady Aerodynamic Derivatives

Theoretical and experimental investigation ofthe flexure-torsion flutter of aerofoils in cascadeare presented. In this first report are shown a computational method and computed results of unsteady lift, drag and moment acting on the vibrating aerofoils in cascade, and some experimental results of these unsteady aerodynamic forces and moment. In computation are included the effects of stagger angle, solidity, attack angle (or steady circulation), inter-blade phase angle of vibration and camber of blade (or distribution of steady circulation). Each aerofoil constituting the cascade is considered to have two degrees of freedom of translational vibration (not necessarily normal to blade chord) and torsional vibration about elastic axis. Agreements between computational and experimental results are satisfactory. The effects of cascade parameters on critical flutter speed of binary flutter analyzed using the aerodynamic derivatives developed in this 1st report are shown in the 2nd report.

Transfer Function of the Middle Ear

The transfer function of the middle ear was investigated in anesthetized cats. The amplitude and phase angle of vibration of the malleus, incus, and round window for constant sound-pressure level at the eardrum was measured by a capacitive probe. The acoustic impedance at the eardrum in the frequency range from 200 to 8000 cps was also measured. The acoustic impedance at the eardrum was found to be proportional to the ratio of sound pressure at the eardrum and velocity of the malleus from about 200 cps to 4 kc/sec, showing that the eardrum acts as a rigid piston in this frequency region. By comparing the amplitude of the malleus and that of the round window, it was found that the coupling between the malleus and the cochlear fluid is very rigid. A second-order low-pass function described by its Laplace transform was found to be a good approximation to the experimental data, up to a frequency of about 4 kc/sec, or approximately 4 times the cutoff frequency. In the frequency range where the eardrum acts as a rigid piston, it is thus possible to estimate the transfer function of the middle ear entirely from the acoustic impedance data in the plane of the eardrum.