Front Of Cylinder Research Articles

Numerical simulations for the flow-induced vibrations of tandem dual flexible circular cylinders

The three-dimensional large-eddy-simulation coupled with a mode superposition method was applied to numerically simulate the flow-induced vibrations (FIVs) of tandem dual flexible cylinders at Re = 1000 with three different spacing ratios (Sx/D = 2.5, 3.5, and 5, Sx is center-to-center spacing for tandem cylinders, and D is the diameter of the cylinder), corresponding to the reattachment flow, transition flow, and co-shedding flow regimes in stationary tandem cylinders, respectively. The effects of Sx/D on structural vibrations, flow fields, distributions of the surface pressures, and energy properties were investigated to reveal the mechanism for the FIV. Increasing Sx/D weakens the influence of the upstream cylinder on maximum response amplitudes and lock-in region for downstream cylinder. The wake patterns for tandem flexible cylinders are more complex compared to stationary or vibrated rigid tandem cylinders. The shielding effect reduces surface pressure on the downstream cylinder significantly when its vibrations are smaller, leading to a decrease in mean power as well. Furthermore, different mechanisms contribute to amplified FIV in downstream cylinders depending on Sx/D: when Sx/D = 2.5, the upstream vortices collide with the downstream cylinder's front surface and merge with the vortices generated by the downstream cylinder, increasing negative pressure on both front and rear surfaces of the downstream cylinders and promoting FIV; however when Sx/D =3.5 and 5, a binary vortex street forms behind the downstream cylinder without obvious negative pressures on its front surface, the dominant causes of FIV are primarily attributed to interactions among upstream and downstream vortices.

Propagation phenomena for a nonlocal reaction-diffusion model with bounded phenotypic traits

In this paper we study the stability of cylinder front waves and the propagation of solutions of a nonlocal Fisher-type model describing the propagation of a population with nonlocal competition among bounded and continuous phenotypic traits. By applying spectral analysis and separation of variables we prove the spectral and local exponential stability of the cylinder waves with the noncritical speeds in some exponentially weighted spaces. By combining the detailed analysis with the spectral expansion and the special construction of sub-supersolutions, we further prove the uniform boundedness of the solutions and the global asymptotic stability of the cylinder waves for more general nonnegative bounded initial data, and prove that the spreading speeds and the asymptotic behavior of the solutions are determined by the decay rates of the initial data. Our results also extend some classical results on the stability of planar waves for Fisher-KPP equation to the nonlocal Fisher model in multi-dimensional cylinder case.

Numerical study flow-induced vibration of four two-degree-of-freedom circular cylinders in lozenge configuration using random vortex- boundary element scheme

Flow-induced vibration around industrial structures is a significant factor contributing to the mechanical degradation of these structures exposed to fluid flow. Numerical simulation of such flows is challenging with conventional simulation methods due to the displacement of the structural boundaries and the complexity of defining and satisfying boundary conditions. In this research, the development and combination of random vortex and boundary element methods have been employed to address the aforementioned challenges. Two-dimensional flow at Reynolds numbers of 100, 200, and 1000 around four two-degrees-of-freedom circular cylinders in two lozenge configurations with different diameter ratios (parallel and vertical diameter to the flow direction) has been simulated. In configuration 1, the diameter ratio is 1.5, the horizontal and vertical diameters are equal to 3 times and 2 times the cylinder diameter, respectively. In configuration 2, the diameter ratio is 1, and the diameter of the lozenge is equal to 4 times the cylinder diameter. The changes in hydrodynamic force coefficients, and streamlines are depicted for each scenario. The oscillation amplitude of the rear cylinders, which is affected by the vortex shedding from the front cylinders, increases. In certain instances, especially at higher Reynolds numbers like Reynolds 1000, increasing in oscillation amplitude may even result in collisions between the cylinders. For configuration 2, both the average drag coefficient and the range of variation for all four cylinders are greater than those for similar cylinders in configuration 1. The results indicate that an increase in the Reynolds number from 100 to 200 and 1000 results in approximately 1.4 and 11.5 times amplification in the oscillations of the drag coefficient, and the maximum value of lift coefficient increases nearly 2.2 and 80 times, respectively.

COMPUTATIONAL ANALYSIS OF FLOW CHARACTERISTICS AROUND A TWIN-SPLINED CYLINDER WITHIN A 2-D CHANNEL

In the present research work, external flow-induced stresses on a circular cylinder with double-splined surfaces are investigated at a Reynolds number Re of 100. Opposite sides of the cylinder have splined surfaces. The splines are positioned between 0° and 90° from the cylinder's front and rear stagnation points. It is demonstrated that the spline on the cylinder's leading edge modifies the vortex dynamics and causes considerable changes in flow-induced forces. At Re = 100, when a spline is placed on a cylinder's surface, noticeable reduction is observed in the coefficients of lift and drag compared to a smooth cylinder. When the inclination angle is increased to a maximum of 60°, the stagnation point moves to the windward side. Additionally, the spline in the front and back side of the cylinder significantly strengthens the vortex flow. At inclinations of 90° and 0°, maximal and minimal vorticities are obtained. Furthermore, the present work's double-spline cylinder demonstrates the advantage of reduced drag over many previously reported bluff bodies.

Application of singular spectrum analysis to nonstationary time series in flow-induced vibrations of a circular cylinder

In numerical simulations of flow-induced vibrations (FIV) of a circular cylinder, abundant time series data are available, including cylinder displacement and acting forces. Singular spectrum analysis (SSA) is employed to deal with nonstationary multi-component time series produced in two FIV cases with proper interpretation in physics. In the first case, the cylinder displacement time series is decomposed into two oscillatory components using SSA. The instantaneous frequencies of these two components are obtained by Hilbert transform (HT) and found to be in agreement with the wavelet transform of the cylinder displacement. In the second case, three oscillatory components are extracted from the cylinder displacement time series by SSA. The dominant component is characterized by steady oscillations at the vortex shedding frequency, which suggests a relatively steady vortex shedding process behind the rear cylinder. In contrast, the second component, which is closely associated with the alternate boundary layer separations from the front cylinder, features in the increasing amplitude with time. This implies that the unsteady flow field in the gap might be attributed to the nonstationary cylinder oscillations. This work demonstrates that SSA, in conjunction with HT, enables a comprehensive time-frequency analysis of nonstationary time series obtained in FIV.

Numerical simulation study on the interaction between a gravity current and horizontal cylinders

Interactions between gravity currents and different types of horizontal cylinders are investigated, with a focus on analyzing the hydrodynamic characteristics of the flow field around the cylinders. The simulation results are compared with experimental measurements to verify the accuracy of the adopted numerical method. The hydrodynamic characteristics, including lift, drag, dynamic pressure and vorticity field around the cylinder, are analyzed. The results indicate that when the height of an individual cylinder increases, the vorticity in the flow field also increases. Additionally, the maximum dynamic pressure around the lower wall of the cylinder is significantly enhanced, which also leads to corresponding changes in the maximum force acting on the cylinder. Furthermore, the interaction between gravity currents and the double cylinder is studied. It can be found that the distribution of the maximum dynamic pressure and vortices around two cylinders relates to the change of the center-to-center distances. When the space is small, the drag force on the front cylinder is considerably smaller than that on an individual cylinder, and the center-to-center distance significantly affects the rear cylinder. The distribution of the maximum force on the cylinder is not obviously influenced by the changes in the cylinder's center-to-center distances.

Experimental investigation on the hydro-acoustic characteristics of tandem cylinders with equal diameters

The investigation of the hydro-acoustic characteristics of tandem cylinders has a great importance because they occur in a variety of maritime applications that include submarines, offshore structures and seabed pipelines systems. Better understanding of the noise generation mechanism of tandem cylinders provides great contribution to reduce noise levels for many engineering applications. In this study, the hydro-acoustic characteristics of tandem cylinders with same diameter were experimentally investigated for five different distance ratios at Reynolds number of 1.6 × 104. The diameter of the front and rear cylinders used in hydro-acoustic experiments is 0.02 m. It is observed that the main peak spectrum becomes narrower as the distance ratio increases. The width of the main peak spectrum also decreases as the flow regime transition from the reattachment regime to the separation regime. An increase in the distance ratio is found to correspond to an increase in the main peak frequency. The maximum sound pressure level is observed to attain its peak value at the critical distance ratio of 3.0. Notably, the maximum sound pressure level exhibits a substantial increase of approximately 6 dB as the distance ratio increases from 1.5 to 3.0, followed by a subsequent decrease of approximately 1 dB between the distance ratios of 3.0 and 6.0.

Numerical investigation of noise suppression and amplification in forced oscillations of single and tandem cylinders in high Reynolds number turbulent flows

The noise generated by a three-dimensional turbulent wake behind an oscillating single or tandem cylinder(s) is studied using detached eddy simulation and the Ffowcs Williams-Hawkings (FW-H) method. This hybrid methodology is validated using some experimental data of a turbulent flow past a single or tandem stationary cylinder(s) and some numerical data (obtained from a direct numerical simulation) of a laminar flow past tandem oscillating cylinders. For an oscillating cylinder at a fixed Reynolds number Re=120,000, the sound energy is suppressed compared to that of a stationary cylinder provided the value of oscillation frequency approaches 57% of the original vortex-shedding frequency of the stationary cylinder. This noise reduction arises from the structural oscillations suppressing the noise generated by the vortex shedding from the stationary cylinder—the additional source of noise stemming from the structural oscillations is too small to compensate for the mechanism responsible for the noise suppression. The noise generated by the cylinder motion includes contributions from the loading and thickness noise, whereas the noise generated by vortex shedding from the stationary cylinder only includes the loading noise. The flow past tandem stationary cylinders exhibits a larger number of spectral peaks in the sound pressure power spectrum and the peaks occur at a lower frequency compared to the flow past a single cylinder. The drag force fluctuations result in the propagation of the sound pressure in the in-line direction, whereas the lift force fluctuations result in the propagation of the sound pressure in the transverse direction. Five different scenarios of stationary and/or oscillating tandem cylinders are studied. The second and third invariants of the velocity gradient tensor are used to visualize the distinct vortex structures in the wake for the five different scenarios of tandem cylinders. A single cylinder oscillating in the transverse direction exhibits a larger sound pressure level (SPL) than the streamwise oscillation of the same cylinder. In contrast, the streamwise (in-line) oscillation of one or the other cylinder in a tandem array results in a larger SPL than the transverse oscillation of one or the other cylinder. Finally, the SPL is more sensitive to the oscillations of the rear (downstream) cylinder than the front (upstream) cylinder.

Effect of lot microstructure variations on detonation performance of the triaminotrinitrobenzene (TATB)-Based insensitive high explosive PBX 9502

PBX 9502 is an important insensitive high explosive due to its combination of safety properties and detonation performance. It is a polymer-bonded formulation consisting of 95 wt.% 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) as the high explosive crystal, bound with Kel F-800 (FK-800), a co-polymer of chlorotrifluoroethylene and vinylidene-fluoride. Two different types are used, one known as virgin that uses only pristine manufactured TATB, and a second known as recycled that has 50 wt.% of its TATB reclaimed from machining scraps of previously pressed virgin PBX 9502. Recycled lots have a higher percentage of fine particles compared to virgin lots, due to the fracturing and damage sustained by TATB crystals during pressing. We examine the influence that this TATB microstructure difference between virgin and recycled PBX 9502 has on detonation performance properties. New rate-stick geometry diameter effect, detonation front shape and cylinder expansion test data are obtained for two previously uncharacterized virgin lots and one recycled lot of PBX 9502. This is combined with previously published data for one virgin and one recycled lot for evaluation purposes. Detonation shock dynamics model calibrations are conducted on each of the five lots to provide an assessment of the detonation timing characteristics of virgin versus recycled PBX 9502 lots. For two of the virgin lots, detonations propagate slower in the rate-stick geometry than those in the two recycled lots. However, the other virgin lot tested has propagation rates comparable to that of the recycled lots for larger diameter rate-sticks. The latter result, though, is shown to be geometry dependent and depends on the range of detonation curvatures accessed in different geometries. New copper-confined, cylinder expansion tests are conducted on each of the three virgin and two recycled lots to obtain detonation product Jones-Wilkins-Lee equations of state, enabling an assessment of the metal push capabilities for each of the five lots. We find that the metal push capabilities, characterized by the evolution of the heat of detonation with volume, are similar between the virgin and recycled lots. Thus, changes in microstructure between different PBX 9502 lots seemingly affect the rate of reaction, but not the overall energy content.

Vortex-induced vibrations of two rigidly coupled circular cylinders in tandem arrangement

In this paper, we study the transverse vortex-induced vibrations (VIV) of two rigidly connected circular cylinders of equal size, arranged in a tandem configuration, by means of two-dimensional numerical computations. Results are examined for Re=250 and a fixed center-to-center separation of 2D. The dynamic response of the two-cylinder system is investigated in detail over a domain of reduced velocities ranging from Ur=2 to 8. The diverse types of branches are identified, on the basis of their distinct characteristics in the amplitude and frequency responses. Among them, the lower branch is of particular interest as it is quasi-periodic in nature, instead of the periodic regime that is well documented for the isolated cylinder case. By scrutinizing the vorticity dynamics, it reveals that this quasi-periodicity arises from the switching between two flow states, which are essentially distinguished by whether an active gap flow is present. The dynamically rich response leads to a rich variety of phase dynamics, involving phase locking, trapping, slipping and drifting; in particular, phase drifting is indicative of a forthcoming phase jump of 180° between the lift force and the displacement. It is also found that in the initial branch, the excitation of the system is driven by the pressure lift force on the rear cylinder; by contrast, in the lower branch, it is the pressure lift force on the front cylinder that acts as a source of excitation.

The influence of cylinders in tandem arrangement on unsteady aerodynamic loads

This paper presents an experimental study on the unsteady pressure loading for two circular cylinders in tandem arrangement for the Reynolds number in the subcritical regime. Experiments were conducted on two heavily instrumented cylinders, each with multiple static and dynamic pressure sensor devices positioned at various peripheral and spanwise locations, enabling extensive dynamic surface pressure, coherence, and turbulence length-scale analysis. Results show that the root-mean-squared pressure magnitude of the pressure distribution results is much larger for the rear cylinder than for the front cylinder. In the case of small spacing ratios, the surface pressure density findings show a decreased shedding frequency on both cylinders, however the critical spacing ratio shows a quick jump in shedding frequency. The lateral coherence results also revealed that beyond the critical spacing, a prominent peak at the fundamental vortex shedding frequency exists, with weaker peaks at shedding harmonics on the front and rear cylinders, resulting in smaller correlation length values than those for smaller spacing ratios. The discovery of tonal peaks and their associated flow mechanics on cylinders in tandem were reinforced by the lift and drag power spectral density as well as the higher-order spectral analysis, such as wavelet analysis and persistence spectrum.

Active vibration control of tandem square cylinders for three different phenomena: Vortex-induced vibration, galloping, and wake-induced vibration

When exposed to fluid flow, elastically supported multiple square cylinders may experience either one or a combination of vortex-induced vibration, galloping, and wake-induced vibration phenomena. Due to these high-amplitude instabilities, it is necessary to utilize vibration control devices. The present paper studies the suppression of flow-induced vibration (FIV) of tandem-arranged square-section cylinders, which can oscillate independently in the streamwise and transverse directions at low Reynolds numbers. The vibration reduction is achieved by directly applying opposing forces using an active FIV control system based on the intelligent proportional-integral-derivative controller. In the present study, the fluid flow equations are calculated through the finite volume technique, by which the aerodynamic forces are attained. Next, based on the computed excitation forces, the motion equations of cylinders are solved within a user-defined function code. The numerical results show that the controller successfully suppresses the vibrations of the front and rear cylinders by a maximum of 94% and 92% at Re = 80 and by 98% and 97% at Re = 100. At Re = 230 and 250, the controller successfully diminishes the oscillation of the front cylinder by a maximum of 79% and 80%, respectively. The significant intensity of the front cylinder's wake makes the active control system unable to capably affect the vibrations of the downstream cylinder at Re = 230 and 250.

Numerical study of injection strategy on the combustion process in a peripheral ported rotary engine fueled with natural gas/hydrogen blends under the action of apex seal leakage

To improve the combustion efficiency of the rotary engine fueled with natural gas/hydrogen blends, the effect of the injection strategy of the blended fuel on the combustion process in cylinder was studied. In addition, considering that apex seal leakage (ASL) is difficult to avoid in the actual working process of rotary engines, the action of ASL was considered in the study. Therefore, a 3D dynamic calculation model of a peripheral ported rotary engine considering the ASL was established. Based on the calculation model, the impact of the blended fuel injection position (BFIP) and the blended fuel injection timing (BFIT) on the combustion process was numerically researched. The results showed that when the fuel injection strategy was Case: B-150, whose BFIP was located at the intersection of the cylinder profile and the long axis with the BFIT of 150°CA (BTDC), the blended fuel was more distributed in the front of cylinder (FOC) and the middle of the cylinder (MOC) at the ignition timing, which effectively avoided the problem of the incomplete combustion in the back of the cylinder (BOC). Therefore, to optimize effectively the combustion performance of the rotary engine, the injection strategy of Case: B-150 was recommended in engineering applications.

Fluid Flow Through Serieal Parallel Circular Cylinder Arranged In Tandem

The Fluid flow through circular cylinders in serieal parallel positions arranged in tandem were analyzed computationally and experimentally at nine levels of Reynolds number, ReD 34,229; 47,921; 61,612; 75,304; 88,996; 102,688; 116,379; 130.071 and 143,763 The variation in the ratio of the distance between the front and rear cylinders is determined as M / D = 0.3, M / D = 0.5, M / D = 0.7, M / D = 0.9, and M / D = 1.1. While the distance between cylinder number 2 and 3 we set constantly and determined as N / D = 5 cm. The results displayed are flow velocity with computational approach validated by flow visualization, computational pressure contour, and drag coefficient through experimental testing. The results showed that the smallest boundary layer thickness was obtained in the model with a distance ratio of M / D = 2.5, using both computational and experimental approaches. The characteristics of the minimum pressure contour and the lowest drag coefficient (CD) = 0.7572 were also obtained at the ratio of the distance M / D = 0.25 and at upstream speed of 21 m / s

Design and experiment of multi-mode steering system of agricultural machinery for hilly and mountainous area

In order to improve the steering flexibility of agricultural machinery in hilly and mountainous areas, a multi-mode steering system with front wheel steering, rear wheel steering, and four-wheel steering has been developed. The hydraulic steering system based on load sensitivity principle and proportion-integration-differentiation (PID) controlling algorithm was designed, which overcomes the negative impact of external load changes on flow control accuracy. The mechanical-hydraulic-controlling coupling model established in the AMESim and the sequential quadratic combinatorial optimization algorithm (SQCOA) was adopted to obtain the optimal combination of PID parameters. The simulation results demonstrate that the parameters such as pressure, speed, displacement of hydraulic cylinders, etc. in different steering modes meet the design requirements. To examine and verify the system performance, the test platform was researched and developed for conducting steering radius and displacement measurement. The experimental data illustrated that the front and rear hydraulic cylinders have good synchronization accuracy in four-wheel steering mode, and the fast switch of steering mode can be realized. The maximum error rate of is steering radius 4.21% and 3.77%, respectively, in two-wheel steering and four-wheel steering modes. The research methods and conclusions can provide a theoretical basis and reference for the other steering system development.

Single-step deep reinforcement learning for open-loop control of laminar and turbulent flows

We introduce single-step proximal policy optimization, a deep reinforcement learning algorithm for situations where neural network optimization does not depend on state. Optimization is examined with open-loop control problems of laminar and turbulent flows (Re up to a few ${10}^{4}$). For turbulent flow past a square cylinder, the approach reduces drag by 30% by finding the best placement of a small control cylinder, in agreement with existing experimental data. For turbulent flow past a fluidic pinball, drag is reduced by 60% by using boat tailing actuation made up of a slowly rotating front cylinder and two oppositely rotating downstream cylinders, matching existing machine learning results.

Flow-induced vibrations of a pair of in-line square cylinders

Flow-induced bidirectional vibrations of two in-line square cylinders of same size and mass ratio (=10) are analyzed at Reynolds number, Re = 100. The cylinders are located in the co-shedding regime, i.e., they are separated by a normalized center-to-center spacing of 5. The reduced speed, U*, is varied from 3 to 15 keeping Re constant. The upstream and downstream cylinders display identical frequency characteristics with U*. Accordingly, the cylinders share identical decomposition of dynamic response. The response is composed of the desynchronization regimes and lower branch; an initial branch does not exist. The vibrations are hysteretic at the lock-in boundaries whereas for a single square oscillator, hysteresis is identified only near the onset of lock-in. Hysteresis in the solutions for U*=7 within the lower branch is reflected in the wake mode of the rear cylinder whereas for the upstream cylinder, wake mode remains identical. The vortex-induced vibration (VIV) of the upstream cylinder is qualitatively similar to that of an isolated square oscillator. Despite the range of lock-in of the cylinders being identical, the VIV of the downstream cylinder departs significantly from its upstream counterpart. The shear layers separated from the front cylinder impinge on the rear cylinder and alter its flow field. The rear cylinder executes high amplitude VIV over the entire lower branch. The symmetry of the drag-lift phase diagrams does not necessarily translate to symmetric phase plots of in-line and cross-stream response. The drag and in-line response of the cylinders are out of phase throughout.

High-order moments of velocity fluctuations around a cylinder in a dredged channel

The effect of a channel pit on the turbulence structure around an embedded cylinder was explored based on the behaviour of high-order moments of streamwise velocity fluctuations. Instantaneous velocities across the flow depth were recorded upstream and downstream of a circular cylinder in a sand bed flume with and without channel dredging. The variance of streamwise velocity fluctuations and higher-order velocity moments around the cylinder were studied for both cases. Logarithmic scaling of was observed in the down-flow upstream of the cylinder and in the wake zone downstream of the cylinder. Higher-order velocity moments up to 2p = 4 and 2p = 6 were also evaluated to validate the logarithmic scaling. The mean flow structure developed due to the fluid–solid interactions around the cylinder was found to govern the scaling characteristics of velocity fluctuations. The experimental data showed that channel dredging increased the near-bed values of at the cylinder front and also increased the peak of turbulence production downstream of the cylinder. These alterations may be linked to excess scour and undermining of bridges due to channel dredging.

Structural design of spiral blade of concrete mixer truck

This article takes a concrete mixer truck actually produced by an enterprise as an example. According to the functions of the three-part spiral blades of the front cone, cylinder, and tail of the mixing drum, combined with theoretical knowledge, the Pro/E software is used to realize the re-realization of the blade spiral. design. A spiral line that is more in line with actual working conditions is derived, which provides a theoretical basis for the design and modeling of spiral blades of concrete mixer trucks.

Mechanical characteristics of drum shearer with large mining height under oblique cutting

In order to study the dynamic characteristics of the shearer with large mining height of 8.8 m under Oblique cutting, the spatial mechanical model of the Shearer under oblique cutting was established, the angle between the drum and the working face, the load of the drum and the dynamic characteristics of the fuselage are analyzed by discrete element method and dynamics. The results show that the maximum feed rate of the front drum is 1940mm, the maximum feed rate of the back drum is 1570mm, and the angle between the front drum and the coal wall reaches a maximum of 8° at 64s, and the cutting resistance of the front drum reaches a maximum at 80s, and finally fluctuates up and down at 3.5×105N, the cutting resistance of the back drum increases with the cutting depth, and finally fluctuates up and down at 3.0×105N. The load of the front drum is 1.2 times of that of the back drum. In the process of Oblique cutting, the support force on the lower surface of the front sliding shoe increases by 3.5×105N, the support force on the lower surface of the rear sliding shoe decreases by 2.5×105N, the support force on the upper surface of the front guiding sliding shoe increases by 1.1×105N, and the support force on the upper surface of the rear guiding sliding shoe decreases by 2.3×105N, the whole machine has the tendency of forward turning and side turning to the coal wall. The average radial force between the front rocker arm and the fuselage pin is about 1.8×106N, the average radial force between the front cylinder and the fuselage pin is about 2.2×106N, and the average radial force between the rear rocker arm and the fuselage pin is about 8.0×105N, the average radial force between the rear cylinder and the PIN shaft is about 1.3×106N, which shows that the radial force at the front of the fuselage, the rocker arm and the height of the pin shaft is obviously larger than that at the rear of the fuselage. The research results are important for the design and development of large mining height shearer.