Flow-induced Vibration Effects Research Articles

Vibration-Enhanced Heat Transfer Analysis and Improvement of Spiral Elastic Tube Heat Exchanger

Using the fluid–solid coupling approach in fluid-induced vibration studies, the effect of flow-induced vibration on a heat exchanger is investigated. This paper analyzes the impact of flow parameters for shell fluid on heat transfer characteristics enhanced by the vibration of a spiral elastic tube bundle (SETB). Improvement schemes for heat exchangers are also proposed, and they are studied and compared. The results show that there is a positive correlation between the inlet velocity and the heat transfer coefficient of the SETB heat exchanger. As the inlet velocity rises to 0.9 from 0.3 m/s, the Nusselt number of the hollow SETB heat exchanger under vibration conditions is increased by 153.10, 45.55, and 26.73% sequentially. The vibration generated by impacting the elastic element during fluid flow can improve the Nusselt number effectively. As the flow velocity increases to 0.9 from 0.3 m/s, the flow-induced vibration enhances the Nusselt number of the hollow SETB heat exchanger by 2.13, 1.53, 1.05, and 0.89%. When the inlet flow velocity of fluid is in the range of 0.3–0.9 m/s, under the same flow velocity, same pressure drops, and same pumping power conditions, the performance of the improved heat exchanger is greater than that of the SETB heat exchanger before the structural improvement.

The Effect of Flow-Induced Vibration on Heat and Mass Transfer Performance of Hollow Fiber Membranes in the Humidification/Dehumidification Process.

Cross-flow hollow fiber membranes are commonly applied in humidification/dehumidification. Hollow fiber membranes vibrate and deform under the impinging force of incoming air and the gravity of liquid in the inner tube. In this study, fiber deformation was caused by the pulsating flow of air. With varied pulsating amplitudes and frequencies, single-fiber deformation was investigated numerically using the fluid–structure interaction technique and verified with experimental data testing with a laser vibrometer. Then, the effect of pulsating amplitude and frequency on heat and mass transfer performance of the hollow fiber membrane was analyzed. The maximum fiber deformation along the airflow direction was far larger than that perpendicular to the flow direction. Compared with the case where the fiber did not vibrate, increasing the pulsation amplitude could strengthen Nu by 14–87%. Flow-induced fiber vibration could raise the heat transfer enhancement index from 13.8% to 80%. The pulsating frequency could also enhance the heat transfer of hollow fiber membranes due to the continuously weakened thermal boundary layer. With the increase in pulsating amplitude or frequency, the Sh number or Em under vibrating conditions can reach about twice its value under non-vibrating conditions.

Numerical Study of the Flow-Induced Vibration During Tunnel Surging at the Intake Section of Chenderoh Dam

Chenderoh Dam that located in Malaysia is one of renewable energy power plant that beneficial to mankind. However, in some cases, the dam suffers from the vibration effect during the water spilling from upstream to downstream. This study focused on major part of the dam which is the intake section during the tunnel surging condition. A detail 3D model of the intake section was constructed and used in the prediction of flow-induced vibration response. The results of frequency domain response and operational defection shapes (ODS) from the effect of flow-induced vibration are compared with the natural frequencies and mode shapes of the dam. From the results, the transient vibration responses due to the flow of water occurred at the frequency of 8.63 Hz with the maximum deformation of 8.24 x 10−1 m, meanwhile, the modal analysis obtained at 2.76 Hz of natural frequency with deformation of 9.1 x 10−4 m. The deformation of ODS is high because of the water flow and tunnel surging condition. However, there is no resonance phenomenon occurred, yet a safety precaution must still be considered by the operator based on this result.

Prediction of the Flow-Induced Vibration Response of the Chenderoh Dam Left Bank Section

Flow-induced vibration is a common phenomenon that happened in any of dam structures during the operational condition. This includes the effect of water spilling from the upstream to the downstream of the dam due to high water volume at the upstream side. the release of water from the dam can be beneficial in generating the electricity source to the surrounding areas. However, in some cases, the spill of water can induced the significant vibration effects to the dam structure. In this study, the prediction of the flow-induced vibration response at the left bank section of the real scale Malaysian Chenderoh Dam model is simulated using the ANSYS software. the input force disturbances from the flow of the water at the left bank section during the normal water spilling condition is investigated. the results of frequency domain response and operational defection shapes (ODS) from the effect of flow-induced vibration are compared with the natural frequencies and mode shapes of the dam. From the results, the transient vibration responses due to the flow of water happened at the frequency of 13.3 Hz while the natural frequency of the left bank section occurred at 52.3 Hz, which indicates that there is no resonance phenomenon for the normal case of water spilling at the left bank section of the dam structure. This result is useful for the dam operation section in order to avoid any disaster of the dam structure.

On Two-dimensional Predictions of Turbulent Cross-flow Induced Vibration: Forces on a Cylinder and Wake Interaction

In this paper a typical fluid-structure interaction scenario is investigated for a turbulent flow past a circular cylinder at a relatively low subcritical Reynolds number. Numerous experimental and numerical studies have been undertaken for a baseline Reynolds number of 4,000 involving a stationary cylinder to study in detail the near wake mean flow and turbulence characteristics. These studies conclusively show that the turbulent wake displays significant coherent periodic structures of large eddies that could be adequately and profitably resolved by “low order modelling” of turbulence. In this study, an unsteady numerical framework is employed for the simulations, incorporating an Arbitrary Lagrangian–Eulerian (ALE) method for the associated grid deformation to simulate the coupled motion of the circular cylinder with a single degree of freedom in the initial zone in a typical cylinder-flow response map or what is called “initial regime”. Particular attention is paid towards resolving the large scales of the fluid motion and the inherent coupling of the cylinder’s motion towards the associated evolution of the time averaged flow field. The flow-induced vibration effects regarding the kinetic energy exchange between the mean flow and the coherent periodic scales are investigated further. The predictions discussed and analyzed in detail in the paper display reasonable agreement with the chosen benchmark tests of the stationary cylinder and suggest that the conclusions outlined regarding the coupled flow-cylinder system potentially provides a valuable contribution to the state of the art.

Effect of flow-induced vibration on local flow parameters of two-phase flow

A preliminary study was conducted experimentally in order to investigate the effect of flow-induced vibration on flow structure in two-phase flow. Two kinds of experiments were performed, namely ‘reference’ (no vibration) and ‘vibration’ experiments. In the reference experiment, an experimental loop was fixed tightly by three structural supports, whereas the supports were loosen a little in the vibration experiment. In the vibration experiment vibration was induced by flowing two-phase mixture in the loop. For relatively low superficial liquid velocity, flow-induced vibration promoted the bubble coalescence but liquid turbulence energy enhanced by the vibration might not be enough to break up the bubble. This leaded to the marked increase of Sauter mean diameter, and the marked decrease of interfacial area concentration. Accordingly, flow-induced vibration changed the void fraction profile from ‘wall peak’ to ‘core peak’ or ‘transition’, which increased distribution parameter in the drift-flux model. For high superficial liquid velocity, shear-induced liquid turbulence generated by two-phase flow itself might be dominant for liquid turbulence enhanced by flow-induced vibration. Therefore, the effect of flow-induced vibration on local flow parameters was not marked as compared with that for low superficial liquid velocity. Since it is anticipated that flow structure change due to flow-induced vibration would affect the interfacial area concentration, namely interfacial transfer term, further study may be needed under the condition of controlled flow-induced vibration.