Time-varying Pressure Distribution Research Articles

Modeling method and dynamic analysis of blade with double friction damping structure considering time-varying pressure distribution

A modeling and analytical method considering contact interface pressure characteristics is presented in this paper. Firstly, a high-fidelity model of a blade with a double friction damping structure is established by solid element, and a three-dimensional friction contact element is used to describe the nonlinear friction interface between the blade contact interfaces. Then, the static pressure distribution characteristics of the contact interface of the blade are obtained through the experimental device of the blade with double friction damping structure, and the accuracy of the pressure characteristics is verified. Based on the static pressure distribution, the time-varying dynamic pressure formula of blade contact interface is derived. The influence of the pressure distribution on the contact characteristics of the contact interface is analyzed and applied to the dynamic calculation of the rotating blade. The influence of different parameters on the blade dynamics is obtained. And the optimum mass ratio of the under-platform damper is obtained by simulating the operation condition of the aero engine blade acceleration process.

Vocal fold dynamics in a synthetic self-oscillating model: Intraglottal aerodynamic pressure and energy.

Self-sustained oscillations of the vocal folds (VFs) during phonation are the result of the energy exchange between the airflow and VF tissue. Understanding this mechanism requires accurate investigation of the aerodynamic pressures acting on the VF surface during oscillation. A self-oscillating silicone VF model was used in a hemilaryngeal flow facility to measure the time-varying pressure distribution along the inferior-superior thickness of the VF and at four discrete locations in the anterior-posterior direction. It was found that the intraglottal pressures during the opening and closing phases of the glottis are highly dependent on three-dimensional and unsteady flow behaviors. The measured aerodynamic pressures and estimates of the medial surface velocity were used to compute the intraglottal energy transfer from the airflow to the VFs. The energy was greatest at the anterior-posterior midline and decreased significantly toward the anterior/posterior endpoints. The findings provide insight into the dynamics of the VF oscillation and potential causes of some VF disorders.

Modeling of fatigue damage of coated bodies under frictional loading

A model of contact fatigue damage of a coated body in high-cycle friction performed using a periodic system of indenters has been proposed. The influence of wear of non-fatigue origin on damage accumulation in the coating and substrate is studied. It is shown that the rate of damage accumulation in the coating decreases but remains unchanged or increases at the coating-substrate interface. Comparison of results for a constant and stochastically time-varying pressure distribution shows that variable loading increases the number of detachments of finite-thickness layers and inhibits contact fatigue damage accumulation at the interface.

Numerical Modeling of the Dynamical Interaction Between Slug Flow and Vortex Induced Vibration in Horizontal Submarine Pipelines

Fatigue life of submarines pipelines is known to depend on many factors, e.g., materials, spanning length, vortex induced vibration (VIV), pipe soil-interaction, etc. In the case of VIV, the external flow due to marine currents can generate the well known alternate vortex shedding regime. In this regime, a time-varying pressure distribution over the surface of the pipeline imposes forces upon the pipeline itself, thus producing vibration with a defined frequency. On the other hand, in recent years some authors have shown that slug flow regime may produce a cyclic damage that could reduce in a significant way the fatigue life of submarine pipelines, thus constituting a governing mechanism in their design. In slug flow regime, slugs traveling in the pipe act as moving gravity loads for the pipeline structure, producing a dynamic response, especially important for the free spans. If both frequencies of the before mentioned effects are closer and, in addition, are in the same range of the natural frequency of the pipeline span, resonance effects can be expected to be reinforced and drastic changes in the dynamics of the pipeline could appear. In this work, a first study of the interaction between slug flow induced vibration in horizontal pipelines and cross-flow response due to vortex shedding is presented. The fluid model was based on the classical wake oscillator model. A numerical model based on the finite difference method was implemented for the structure. Two particular extreme cases were modeled to analyze the pipeline dynamics for “small-size” and “large-size” slugs, for a range of marine current velocities. For the case involving small-size slugs, it was observed a near 10% increment in the vibration amplitude (compared to a reference value), while in the case of “large-slugs” the VIV was overweighed by the slug induced vibration (SIV) phenomenon.

Time-Varying Pressure Distribution on Solar Updraft Tower (an Axisymmetric Structure) Induced by a Translating Downburst

The characteristics of time-varying mean wind pressure distribution on the surface of solar updraft tower (SUT, an axisymmetric structure) in a translating thunderstorm downburst is discussed based on revised Chen and Letchford’s empirical model, in which Wood et al.’s empirical model for vertical profile of radial velocity, revised Poreh and Cermak’s empirical model for horizontal profile of radial velocity by considering the full time variation of downburst jet intensity, and Holmes and Oliver’ empirical model for the time function are utilized. The results show that the time histories of mean wind pressures at the points around the circular surface are complex due to the moving of stagnation points for the SUT. The time fluctuation is driven by the summation of the moving of downburst and the characteristics of pressure distribution on the SUT.

Computations of Insect and Fish Locomotion with Applications to Unconventional Unmanned Vehicles

Living creatures such as insects, birds, and fish generate lift and thrust most often by executing large-amplitude wing flapping, possibly with substantial shape deformation from root to tip. The flow for these motions is unsteady, and conventional steady-state aerodynamics is unable to correctly compute the time history of their flapping-force generation. Three-dimensional unsteady computations of flapping about the deforming wing or fin surface are necessary to correctly predict the lift and thrust throughout the flapping cycle. It is only by executing such computations for creatures or vehicles with moving and deforming surfaces that we can gain insights into the time-varying pressure distribution on all surfaces and how that results in flapping-force generation. This can be coupled with visualization of the origination and evolution of body, wing, and wake vorticity. Three-dimensional unsteady flow computations of the flapping flights of the fruit fly, a pectoral-fin swimmer (the bird wrasse), and a variety of unmanned air vehicles were carried out in pursuit of this information. The performance of these flapping wings under gust conditions was also investigated. The effect of fin deformation on the force production was studied. Novel biomimetic vehicles, incorporating information gained from these computations, were designed and built and their performance is described.

Cascade Wind Tunnel Experiment of Stall Flutter.

Stall flutter of a compressor cascade is studied by experiment using a wind tunnel with a linear cascade of blades oscillating in a torsional mode. The time varying pressure distribution on the blade surface and the unsteady velocity fluctuation in the blade passages are measured with pressure transducers and hot wire velocimeters. The experimental result shows that the synchronization and the entrainment occur between the blade oscillation and the rotating stall, and that these phenomena have dominant influence both on the unsteady flow behavior and on the flutter excitation of the oscillating blades. The experimental result agrees very well in general with the numerical result performed in advance using a discrete vortex modeling, particularly concerning the relationship between the occurrence of the stall flutter and the propagation of the rotating stall.