Vortex Shedding Characteristics Research Articles

Analysis of vortex shedding characteristics and heat transfer performance of staggered tube bundle system

Tube bundle systems' heat transfer is unclear due to complex flow channels and turbulent fluctuations, affecting energy efficiency. This study simulates 2D staggered 18-row tube bundles at Reynolds numbers 3,100-50,000. 3D cylinders are simplified to 2D tubes, with grid independence and model validation. Flow, temperature fields, and synergy angles are analyzed for positions, Reynolds numbers, and spacings. High vortex shedding frequency in front tubes with multiple subfrequencies at different amplitudes. Asymmetric solutions emerge due to turbulent fluctuations. At high Reynolds, vortex shedding patterns complexify and frequencies rise. Nusselt number and synergy angle trends similar at low Reynolds, but diverge at high Reynolds. Small tube spacings significantly impact heat transfer; large spacings have weaker effects.

Enhanced performance of cutting angle cylinder piezoelectric energy harvester via coupling vortex-induced vibration and galloping

This paper proposes a novel flow-induced vibration piezoelectric energy harvester with various cutting angle cylinders (FIVPEH-C), for coupling vortex-induced vibration and galloping as well as improving the energy harvesting efficiency. The conceptual designing of the piezoelectric energy harvester with different cutting angle cylinders is conducted, the theoretical models of fluid–structure-electric multi-physical coupled fields are derived, the aerodynamic parameters are solved by three-dimensional computational fluid dynamics (CFD) simulation, and the experimental prototypes of the harvester system are fabricated. The accuracy of the theoretical model is verified by the experimental results. The flow field reveals the vortex shedding characteristics and mode conversion mechanisms. The cutting angle cylinder bluff body transforms the formation mode, initial shape, and intensity of the vortices at the microscopic level, which in turn affects the shedding mode and distance of the vortices at the macroscopic level. When α = 0° and β = 0°, the maximum output voltage of the FIVPEH-C is 13.36 V, and the enhancement ratio reaches up to 108.01 % over the conventional one, which verifies better harvesting performance. This work provides important guidance for designing more efficient piezoelectric energy harvesters via various cutting angle cylinders.

Experimental and numerical investigation on the wake flow and vortex shedding of a rotating circular cylinder

When fluid passes through a still cylinder, alternate shedding vortices are formed on the two sides of the cylinder in the wake. Regarding a rotating circular cylinder, the rotation can affect the wake flow and vortex shedding pattern. To investigate the wake flow and surface pressure characteristics of a rotating cylinder at different rotational speeds, wind tunnel tests and numerical simulation methods through Fluent were used. The dimensionless rotational speed was discussed for its impact on the vortex shedding intensity and pattern. Additionally, the correlation between the cylinder surface wind pressure and the vortex shedding pattern was analyzed. The results of this study provide useful insights into the mechanisms underlying the vortex shedding phenomenon and the effects of rotational speed on the wake flow and surface pressure of a rotating cylinder. The results show that an increase in the dimensionless rotational speed will change the characteristics of the wind pressure distribution, leading to the variation in aerodynamic coefficients. On the other hand, the vortex shedding characteristics of the wake flow will also be affected, with changes in the vortex shedding pattern and direction, thereby changing the characteristics of the wake deviation angle and correlation. Based on the analysis of wake flow speed power spectrum characteristics and the Reynolds number effect, the mechanism of the vortex shedding change caused by flow transitions is speculated and verified by numerical simulation of the vorticity field.

Vortex shedding characteristics and hydrodynamic forces of stationary and elastically mounted side-by-side cylinders fitted with small diameter control rods

Vortex shedding behind bluff bodies can induce noise and vibration problems when it engages in a feedback cycle of oscillations with an acoustic or structural mode. Therefore, several passive and active flow control techniques have been developed to suppress vortex shedding behind a single bluff body. However, less attention was given to the case of multiple bluff bodies in cross-flow. Therefore, in this paper, a numerical investigation is performed to study the effect of adding small diameter control rods in the vicinity of two side-by-side cylinders on the vortex shedding characteristics, the hydrodynamic fluid forces, as well as the suppression of vortex-induced vibration. The simulations are conducted at a Reynolds number of Re = 200 and the side-by-side cylinders have a spacing ratio of T∗=2.5. The number of control rods and their angular positions around the main cylinders are varied. Fitting the side-by-side cylinders with control rods has resulted in three different flow regimes compared to the base case with no control rods. These flow regimes depend on the angular positions of the control rods and they are classified as; bistable flow, stable biased flow, and merged wake flow regimes. The stable biased flow regime has resulted in the maximum reduction of the fluctuating lift coefficient of the side-by-side cylinders, especially when the control rods are placed at θ=135° from the flow stagnation point. Increasing the number of control rods around the cylinders has further reduced the fluctuating lift coefficient and produced a more symmetric wake at the rod angles which produce the stable biased flow, and the merged wake flow regimes. The vortex-induced vibration of the side-by-side cylinders is investigated when the control rods are placed at the angular position that results in a stable biased flow regime. It is revealed that fitting the cylinders with control rods at an angular position of θ=135° has resulted in reducing the vibration amplitude over the whole range of the simulated reduced flow velocities, which makes this technique a viable one to control the vortex shedding and the vortex-induced vibration of side-by-side cylinders.

Investigation of Vortex-Induced Vibration of Double-Deck Truss Girder with Aerodynamic Mitigation Measures

The long-span double-deck truss girder bridge has become a recommend structural form because of its good performance on traffic capacity. However, the vortex-induced vibration (VIV) characteristics for double-deck truss girders are more complicated and there is a lack of related research. In this research, wind tunnel tests were utilized to investigate the VIV characteristics of a large-span double-deck truss girder bridge. Meanwhile, the VIV suppression effect of the aerodynamic mitigation measures was measured. Furthermore, the VIV suppression mechanism was studied from the perspective of vortex shedding characteristics. The results indicated that the double-deck truss girder had a significant VIV when the wind attack angles were +3° and +5°. The aerodynamic mitigation measures had an influence on the VIV response of the double-deck truss girder. The upper chord fairing and lower chord inverted L-shaped deflector plate played a crucial role in suppressing VIV. Numerical analysis indicated that vortex shedding above the upper deck or in the wake region may dominate vertical VIV, while vortex shedding in the wake region of the lower deck may dominate torsional VIV. The upper chord fairing and lower chord inverted L-shaped deflector plate disrupted the original vortex shedding pattern in both regions, thereby suppressing VIV. This research can provide a foundation for bridge design and vibration suppression measures for large-span double-deck truss girder bridges.

Experimental investigation on the vortex-induced vibration of an inclined flexible pipe and the evaluation of the independence principle

This paper reports the experimental results of the vortex-induced vibration (VIV) response of an inclined flexible pipe with various oblique angles (θ) ranging from 0° to 60°. The flexible pipe with an aspect ratio of 75 was fixed at both ends. The VIV response was examined in the reduced velocity range of 4.02–17.55 to evaluate the IP (independence principle) validity. The experimental results illustrate that the spatial distribution of response amplitudes and associated modal weights varies with θ, and the differences are enlarged in the mode transition cases. With increasing the θ, the onset normal reduced velocity (Urn) of mode transition shifts to a lower value and the Urn range of mode transition is narrowed gradually. Additionally, the mode competition is enhanced, resulting in pronounced traveling waves with accelerated propagation speed. The vortex shedding pattern varies along the span, presenting the 2S (two vortices are shed per cycle) and P + S (a pair of vortices and a single vortex are shed from two sides of the cylinder in one cycle) patterns at the upstream and downstream pipe segments, respectively. The streamwise distance between two adjacent vortices is enlarged with the increase in θ. The pipe placed with different inclined angles presents different partitions of coupling pattern, and the Urn range of each sub-region is different. By comprehensive consideration of the spatial–temporal evolution of VIV response, the mode transition features, the coupling pattern, and vortex shedding characteristics, the IP is invalid in predicting the VIV of flexible pipe.

Enhanced performance of piezoelectric energy harvester by two asymmetrical splitter plates

This paper proposes a novel vortex-induced vibration piezoelectric energy harvester attached to two asymmetrical splitter plates (VIVPEH-S), which aims at converting the vibration mode from vortex-induced vibration (VIV) to galloping and improving the energy harvesting efficiency. The conceptual designing of VIVPEH-S with two asymmetrical splitter plates under various installation angles is first conducted, the experimental prototypes are then fabricated and the wind tunnel experimental system is constructed, and the simulation model of the harvester system is finally established. The effects of the installation angles of two asymmetrical splitter plates on the vibration characteristics and harvesting performance of VIVPEH-S are experimentally investigated, and the vortex shedding characteristic and mode conversion mechanism are revealed by CFD simulation. The results demonstrate that the installation of the asymmetrical splitter plates changes the vortex shedding characteristics and transforms the vibration mode from VIV to galloping, which can significantly broaden the working bandwidth, and improve the energy harvesting performance. A maximum enhancement ratio of the output power of VIVPEH-S with α = 60° and β = 90° is up to 471.2% over the conventional VIVPEH. This work provides an important foundation for designing a more efficient piezoelectric energy harvester by using asymmetrical splitter plates.

Drag Reduction for Flow Past Circular Cylinder Using Static Extended Trailing Edge

AbstractA numerical study has been carried out on the two-dimensional flow past a circular cylinder. In this case, a splitter plate is provided at the rear stagnation point in the downstream direction. ansys fluent has been used to carry out the numerical simulations based on finite volume method approach. Grid independence was achieved and the numerical model was validated with results available in open literature at Reynolds numbers of 100, 5000, and 100,000 respectively. In the present investigation, the characteristics of vortex shedding due to the presence of splitter plate in the circular cylinder were investigated. The main focus of this research was to find the optimal splitter plate length for low, moderate, and high Reynolds numbers. It was observed that at low, moderate, and high Reynolds numbers, the drag coefficient (cd) for optimal plate length decreased drastically as compared to the baseline circular cylinder case. Moreover, the fluctuating nature of lift coefficient (cl) had also ceased. This research work has a good potential to decrease time-varying structural loads on bluff bodies by decreasing the vortex shedding frequency and consequently decreasing drag. The scope of our research extends to structures of bridges and large vehicles, radiator pipes of heat exchangers, landing gears of aircraft, and many more.

VORTEX SHEDDING CHARACTERISTICS OF A FLOW-INDUCED VIBRATING CYLINDER: EFFECT OF RIGID VERSUS FLEXIBLE SPLITTER PLATE

VORTEX SHEDDING CHARACTERISTICS OF A FLOW-INDUCED VIBRATING CYLINDER: EFFECT OF RIGID VERSUS FLEXIBLE SPLITTER PLATE

Flow visualization observation of the interference vortex flow from a pair of square cylinders

In order to investigate the aspect of the mutual interference flow from two square cylinders, the visual water-flow observation experiment was performed. In the experiment, the pitch ratio L/d and the arrangement angle α were made into the parameter, and investigation of vortex shedding frequency or the flow pattern was performed. The pitch ratio L/d is 3 kinds, 1.13, 1.89 and 4.15, and an arrangement angle α is 7 kinds per 15 degree from 0 degrees to 90 degrees. The water flow velocity U was 0.04 m/s which correspond to the Reynolds number about 850. As the result of experiment, the complicated flow becomes clear by classification by color of tracer ink, and the aspect of the mutual interference vortex flow can understand better. Even if the pitch ratio was the same, the vortex shedding characteristics changed with arrangement angles. If an arrangement angle is smaller than a geometric duplication angle, the vortex shedding frequency from each square cylinder is the same. On the other hand, when an arrangement angle is larger than the geometric projection angle, the vortex shedding frequency from each square cylinder differs. In the smallest pitch ratio as L/d= 1.13, it is not dependent on the arrangement angle, and produce mutual interference.

Numerical analysis of flow shedding over an obstacle at low Reynolds number

This is a numerical investigation of the unsteady mixed convective flow over an isothermally heated circular cylinder. The flow is directed vertically downwards with buoyancy forces in the opposite direction. A parametric analysis was conducted at five Reynolds numbers Re=10,20,30,40,100, and for Richardson numbers between Ri=0 and 0.5, to evaluate the influence of thermal buoyancy on the instantaneous flow behaviour, vortex-shedding characteristics, thermal fields, and mean heat-transfer rates. The simulations show that at the highest Reynolds number investigated, Re=100, the normal periodic von Kármán vortex street still characterises the flow as Richardson number is increased; however, the oscillation frequency decreases and the oscillation amplitude increases. For Re≤40, a new vortex street appears, named the “Buoyancy-Opposing Vortex Street”, due to thermal buoyancy modifying the von Kármán street. Interestingly, at very low Re=20 and 10, the von Kármán street completely disappears in the heated wakes, whereas the “Buoyancy-Opposing Vortex Street” remains as the sole vortex street characterising the flow.

Characteristics of vortex shedding in the wake of a sphere with a uniaxial through-hole

Wake flows have significant effects on vehicles, buildings, and other objects encountered in daily life. Thus, wake control techniques are of practical importance and have been extensively investigated. One passive wake-control technique is to create a vent on a bluff body, which has been determined to be effective for wake control on a circular cylinder but has not been sufficiently studied for wake control on a sphere. Therefore, this study examined the effect of the vent angle on the characteristics of the wake of a sphere. A sphere with a uniaxial through-hole (vent) was placed in a uniform flow, and the vent angle was varied in the streamwise direction. The Strouhal number in the high-frequency and low-frequency modes was examined. The flow field in the sphere wake varied with respect to the vent angle. Three frequency modes (high, low, and very low), the occurrence of a switching phenomenon, wherein the velocity fluctuated between positive and negative values, and high-frequency energy injection by the vent were observed. In addition, a high dominant frequency was observed only in the positive velocity fluctuation region.

Vortex shedding characteristics and aerodynamic forces of a finned cylinder in cross-flow

The vortex shedding characteristics and aerodynamic forces of a crimped, spirally finned cylinder in cross-flow are experimentally investigated within Reynolds number range of 20×103≤ ReDeq ≤60×103, where Deq is the equivalent diameter. Three different finned cylinders with varying fin pitch-to-root diameter ratios (p/Dr) are studied and compared to their equivalent diameter (Deq) bare cylinder. In comparison to the bare cylinder, the finned cylinders exhibit a notably enlarged vortex formation length. This is due to a lower Coriolis acceleration as a result of a lower vortex force within the formation region. Reduction in the p/Dr led to a progressive increase in the vortex force. This led to a gradual decrease in the vortex formation length. Moreover, the increase in the vortex force resulted in a notable increase in the transverse Reynolds stresses and the development of more concentrated vortex cores. Indicative of a more correlated vortex shedding process, at certain p/Dr, the contribution of the coherent portion of the transverse Reynolds stresses to the total transverse Reynolds stresses exceeded that of the bare cylinder. However, due to the weaker vortex force, the amplitude of the periodic portion of the transverse Reynolds stresses never exceeded that of the bare cylinder. Although for certain p/Dr, the vortex shedding process was more correlated, the combination of an elongated vortex formation length and lower vortex force resulted in weaker dynamic loading on the finned cylinders in comparison to the bare cylinder case. The findings of this study show that the equivalent diameter approach is flawed, as it does not capture any of the intrinsic changes in the flow characteristics and hence the dynamic loading on the finned cylinders.

Interactions between polymers and flows in macro and micro length scales.

Polymer solution with large molecular weights show scale dependent nonlinear behavior. The dynamics of such polymer solution in a meter length scale are very different from those in a micrometer length scale. To clarify this scale dependent behavior, we have conducted several experiments that focus on interactions between polymers and flows in multiple length scales [1Hidema R. Suzuki H. Hisamatsu S. Komoda Y. Furukawa H. Effects of the extensional rate on two-dimensional turbulence of semi-dilute polymer solution flows.Rheol. Acta. 2013; 52: 949https://doi.org/10.1007/s00397-013-0733-3Crossref Scopus (13) Google Scholar, 2Hidema R. Suzuki H. Hisamatsu S. Komoda Y. Characteristic scales of two-dimensional turbulence in polymer solutions.AICHE J. 2014; 60: 1854https://doi.org/10.1002/aic.14364Crossref Scopus (15) Google Scholar, 3Hidema R. Murao I. Komoda Y. Suzuki H. Effects of the extensional rheological properties of polymer solutions on vortex shedding and turbulence characteristics in a two-dimensional turbulent flow.J. Non-Newtonian Fluid Mech. 2018; 254: 1https://doi.org/10.1016/j.jnnfm.2018.02.001Crossref Scopus (12) Google Scholar, 4Hidema R. Fukushima K. Yoshida R. Suzuki H. Vortex deformation and turbulent energy of polymer solution in a two-dimensional turbulent flow.J. Non-Newtonian Fluid Mech. 2020; 285104385https://doi.org/10.1016/j.jnnfm.2020.104385Crossref Scopus (3) Google Scholar, 5Fukushima K. Kishi H. Suzuki H. Hidema R. Modification of turbulence caused by cationic surfactant wormlike micellar structures in two-dimensional turbulent flow.J. Fluid Mech. 2022; 933: A9https://doi.org/10.1017/jfm.2021.1058Crossref Scopus (1) Google Scholar, 6Hidema R. Hayashi S. Suzuki Hiroshi Drag force of polyethyleneglycol in flow measured by a scanning probe microscope.Phys. Rev. Fluids. 2019; 4074201https://doi.org/10.1103/PhysRevFluids.4.074201Crossref Scopus (2) Google Scholar, 7Hidema Ruri Fujito Ken-ya Suzuki Hiroshi Drag force of polyethyleneglycol in flows of polymer solutions measured by a scanning probe microscope.Soft Matter. 2022; 18: 455https://doi.org/10.1039/D1SM01305JCrossref PubMed Google Scholar].In the first part of this talk, I will highlight characteristic vortex deformation and energy transfer caused by polymers in a two-dimensional turbulent flow [1Hidema R. Suzuki H. Hisamatsu S. Komoda Y. Furukawa H. Effects of the extensional rate on two-dimensional turbulence of semi-dilute polymer solution flows.Rheol. Acta. 2013; 52: 949https://doi.org/10.1007/s00397-013-0733-3Crossref Scopus (13) Google Scholar, 2Hidema R. Suzuki H. Hisamatsu S. Komoda Y. Characteristic scales of two-dimensional turbulence in polymer solutions.AICHE J. 2014; 60: 1854https://doi.org/10.1002/aic.14364Crossref Scopus (15) Google Scholar, 3Hidema R. Murao I. Komoda Y. Suzuki H. Effects of the extensional rheological properties of polymer solutions on vortex shedding and turbulence characteristics in a two-dimensional turbulent flow.J. Non-Newtonian Fluid Mech. 2018; 254: 1https://doi.org/10.1016/j.jnnfm.2018.02.001Crossref Scopus (12) Google Scholar, 4Hidema R. Fukushima K. Yoshida R. Suzuki H. Vortex deformation and turbulent energy of polymer solution in a two-dimensional turbulent flow.J. Non-Newtonian Fluid Mech. 2020; 285104385https://doi.org/10.1016/j.jnnfm.2020.104385Crossref Scopus (3) Google Scholar, 5Fukushima K. Kishi H. Suzuki H. Hidema R. Modification of turbulence caused by cationic surfactant wormlike micellar structures in two-dimensional turbulent flow.J. Fluid Mech. 2022; 933: A9https://doi.org/10.1017/jfm.2021.1058Crossref Scopus (1) Google Scholar]. The effects of the extensional rheological properties of polyethylene oxide solutions were focused to understand the vortex deformation in turbulent flow and turbulent statistics of the polymer solution. In the polymer solution, although the turbulent energy production was virtually zero, a characteristic peak appeared in turbulent energy. The results imply the extension and relaxation of polymers affect the energy transfer.In the second part, I will introduce a method to measure the drag force due to synthetic polymers in flowing fluids by using a scanning probe microscope [[6]Hidema R. Hayashi S. Suzuki Hiroshi Drag force of polyethyleneglycol in flow measured by a scanning probe microscope.Phys. Rev. Fluids. 2019; 4074201https://doi.org/10.1103/PhysRevFluids.4.074201Crossref Scopus (2) Google Scholar,[7]Hidema Ruri Fujito Ken-ya Suzuki Hiroshi Drag force of polyethyleneglycol in flows of polymer solutions measured by a scanning probe microscope.Soft Matter. 2022; 18: 455https://doi.org/10.1039/D1SM01305JCrossref PubMed Google Scholar]. The conformation of polymers attached to the cantilever probe was predicted, and the drag force due to the deformed polymers in a flow was calculated. The drag forces obtained by model calculations were compared to the force detected by experiments, and found to be reasonably close.

Multi-Mode Motion Dynamics of a Top Tensioned Riser Excited by Vortices and Varying Tension

A coupled model of a top tensioned riser (TTR) under combined excitations from vortices and time-varying tension is proposed. And the van der Pol oscillator is introduced to simulate the time-varying characteristics of vortex shedding. The first three mode approximations as a six degree-of-freedom (DOF) system of vibrations of the fluid-structure interaction system are derived. Two cases of resonances are analyzed by using the numerical method. One case is on the vortex induced vibration (VIV) of the six DOF system, where the 1-to-1 internal resonance (also named “lock-in” phenomenon) between frequencies of the first modes of structure and the wake oscillator are investigated. Bifurcation curves between dynamic responses in terms of the shedding frequency are derived. Comparing to the vibrations of the first order mode, the “lock-in” phenomenon for vibrations of the higher order modes can occur in the wider parameter range with large values. The second case is on the combined resonance between the 1-to-1 internal and 1-to-2 parametric resonance. Response curves versus the shedding frequency under different amplitude ratios are calculated by the Runge–Kutta method. Effects of system parameters including the amplitude ratio of the parametric excitation, shedding frequency on the response curves are investigated. Comparing to the case when only considering the 1-to-1 internal resonance in the VIV, results of the combined resonance show those large-amplitude responses of the structure and wake oscillator can be induced. Responses will increase rapidly as the amplitude of the varying tension increases. Unstable responses can occur within a large frequency band of nondimensional shedding frequency. Furthermore, the dynamic characteristics of the responses of the six DOF system including the bifurcation diagrams, time histories, phase-plane projection and Poincaré sections are computed for different amplitude ratios. Results indicate that complex dynamics such as the quasi-periodic and chaotic solutions can occur for different amplitude ratios. The analysis can be helpful for the parameter design of deep-water risers.

Investigation on the unsteady pressure pulsations and related vortical structures in a molten salt pump

AbstractThe high‐temperature molten salt pump (MSP) is the core equipment of the thermal storage system for concentrating solar power plants, which circulates the molten salt of the thermal storage medium. This study employs numerical simulation of a two‐stage MSP with a storage tank to find the correlation between pressure pulsations and the evolutions of vortical structures based on renormalization group k‐ε turbulence model. It is shown that rotor/stator interaction is the most significant excitation source of pressure pulsations with the prominent excitations being the diffuser passing frequency (fDPF) in the impeller and the blade passing frequency (fBPF). Furthermore, Q‐criterion is employed to capture the periodic shedding vortexes with a frequency of about 3fR at the suction surface and the trailing edge in diffusers. Impinging vortex and shedding vortex with the frequency 6fR on the leading edge of the diffuser is captured. The vortex shedding characteristics are significantly different under various conditions, and the separation vortexes appear at the leading edge of pressure surface in the diffusers at higher flow rates. Finally, it is obvious that the excited components and their magnitudes in the pressure spectrum are closely associated with the unsteady vortical structures within the model pump.

Fluid-structure coupled analysis of flow-induced vibrations in three dimensional elastic hydrofoils

Hydrofoils have been widely used in ocean and offshore structures. The research on their elastic response in turbulent flow is quantitatively challenging, and it is of great interest for consideration in engineering applications. In this study, a fluid-structure coupling numerical simulation of a three-dimensional elastic hydrofoil is performed. The SST (shear stress transfer) k-ω turbulence model is used to simulate the vortex shedding and near-wall flow characteristics with different Reynolds numbers. By coupling the FVM (finite volume method), the elastic response of the hydrofoils is analyzed. Furthermore, the formation and evolution of the trailing vortex is described. The elastic vibration and subsequent stress distribution of the hydrofoil caused by the vortex shedding are investigated. Moreover, the frequency domain characteristics of the vibration and turbulence field are analyzed. The results show that resonance occurs when the frequency of the vortex induced flow field fluctuations matches the natural frequency of the hydrofoil. This leads to intense hydrodynamic fluctuations in the time domain. In addition, the dynamic responses of the hydrofoil will “lock-in” to its natural frequency within a certain range of flow velocities. Although the frequency lock-in is often accompanied by resonance, lock-in phenomena cannot be solely attributed to resonance, which is caused by hydrofoil switching between the free and forced vibration regimes. The frequency lock-in is caused by the dominant frequency modulation induced by the fluid motion, thus, it can exert non-negligible effects on the flow field via fluid-structure coupling.

Vortex shedding and evolution induced by the interactions between a solitary wave and a submerged horizontal plate

This paper presents results of a solitary wave propagating over a submerged horizontal plate based on a non-hydrostatic model. A high-resolution advection scheme is employed based on a second-order flux-limiter method. The model is first validated by comparing numerical results with recently obtained measured data. Then, a series of simulations are carried out to investigate the effect of the plate length on the characteristics of vortex shedding and evolution. With the increase in the length of the plate, more dominant vortical structures induced by the solitary wave with the same wave height can be identified near the lee side of the plate. There are two separate positive vortex shedding from the lower corner of the plate near the lee side, which are not presented in experiments. The secondary positive vortex leads to the water surface deformation for the case that is close to the limit when wave breaking occurs.

Shedding vortex characteristics analysis of NACA 0012 airfoil at low Reynolds numbers

In this paper, the vortex shedding characteristics been numerically simulated for Re = 1 × 104 by computational fluid dynamics (CFD), which caused by flow separation of NACA0012 airfoil. What is more, the variation of vortex shedding structure and the corresponding frequency characteristics of vortex shedding at different angles of attack are studied. The results reveal that with the increase of the angle of attack, the flow state around the airfoil will change from steady state to unsteady state, the vortex structure of the suction surface will become more and more complex with the increase of the angle of attack. In the periodic wake vortex shedding flow field, according analysis of the vortex structure and vortex shedding frequency, the vortex shedding will show 2S (Single) mode (8°∼15°) - chaotic state (16°∼18°) - 2S (Single) model (19°)- quasi periodic flow (20°∼24°) with the increase of angle of attack for α>7°. The rising section and falling section of airfoil lift and drag coefficient curves correspond to the vortex shedding and formation respectively. The frequency spectrum corresponding to the lift coefficient can be used to analyze the characteristics of vortex shedding from the perspective of frequency domain. With the increase of the angle of attack, the stability of flow field decreases, and the Strouhal number of vortex shedding frequency decreases basically. The order of the Strouhal number in different flow field states is 2S mode > quasi periodic flow > chaotic state. Among them, most of the Strouhal number corresponding to 2S mode fluctuate around 0.2, and the Strouhal number corresponding to chaotic state and quasi periodic flow fluctuate around 0.02 and 0.07 respectively

Numerical investigations into supercavitating flows and hydrodynamic characteristics of a heaving hydrofoil

This paper presents the effects of heaving motions on the hydrodynamic characteristics, supercavitating flow regimes and vortex structures for a two-dimensional (2D) supercavitating hydrofoil. The sinusoidal heaving motion of the supercavitating hydrofoil is realized by overset grid technology. The lift coefficient, drag coefficient, supercavitating flow regime and vortex structures around the supercavitating hydrofoil are analyzed and compared among different amplitudes of the heaving motion. The predicted cavities and the hydrodynamic characteristics are in good accordance with the experiments at a stationary state. The lift coefficient and drag coefficient of the heaving hydrofoil present a sinusoidal law, which is related to the effective angle of attack. The heaving motion would affect the cavity length and its thickness. The greater the heaving amplitude, the greater the difference in cavity pattern at different heaving positions. The cavity variation would affect the shear layer and thus change the vortex shedding characteristics, which are different from those at a stationary state.