Large-scale Cavity Research Articles

Cavitation flow of hydrofoil surface and turbulence model applicability analysis

To improve the simulation accuracy of hydrofoil unsteady cavitation, a user-defined density function is used to correct a variety of turbulence models and combined with a hydrofoil with an angle of attack of 8° for numerical simulation of unsteady cavitation. This study aims to find the optimal turbulence model and apply it to other hydrofoil types to verify its applicability. The results show that the corrected RNG k-ε turbulence model and SST k-ω turbulence model can better fit the experimental results in terms of cavitation morphology and cavitation shedding frequency. The frequency error of cavitation detachment for the corrected SST k-ω turbulence model is just 0.3% compared to the experimental results, and it shows an improvement of approximately 67% over the uncorrected SST k-ω turbulence model. The corrected SST k-ω turbulence model can more accurately capture the shedding cavitation due to the re-entrant jet, better capture the generation of the attached cavitation edge of the U-shape, the shedding of large-scale cavities, and the collapse of the shedding cavitation downstream. Furthermore, the optimal turbulence model has a good applicability in different dimensions and on different hydrofoil types.

Eulerian–Lagrangian multiscale numerical analysis of multimodal partial shedding dynamics

The objective of this paper is to investigate the multimodal partial shedding dynamics from a multiscale perspective of cloud cavitating flows under two distinct cavity shedding mechanisms, namely the re-entrant jet mechanism and the shock wave propagation mechanism. A two-way Eulerian–Lagrangian coupling algorithm is applied to capture the multiscale vapor topologies from microbubble to large-scale cavities. The large-scale cavity evolution is solved through large eddy simulations (LES) with the volume of fraction (VOF) method in Eulerian frame. The sub-grid microbubbles are tracked in Lagrangian frame based on the discrete bubble model (DBM) method. The predictions agree well with experimental observation of the periodical cavity evolution and microbubble dynamics under both the re-entrant jet mechanism and shock wave mechanism around a NACA66 hydrofoil. The numerical simulation provides detailed analysis of the cavitating turbulent flow on the microbubble behavior with emphasis on the spatial-temporal distribution characteristics of microbubbles. The results show that the number and mean size of microbubbles in the cavitation region increase gradually with the growth of attached sheet cavity, development of re-entrant jet and collapse of largescale cavity for both cavitation patterns. Meanwhile, microbubbles are mainly distributed on the largescale interfaces where have high value of vorticity and turbulent kinetic energy under the effect of re-entrant jet and vortex structures. And the probability density functions (PDFs) of microbubble exhibit gamma distributions with a dominant peak at approximately 50 μm for both shedding mechanisms. However, the shock wave formation and propagation process only occurs in the final stage of cavitating flow under shock wave mechanism causing the condensation of vapor and the decrease of the number and mean size of microbubbles. Moreover, the microbubbles are uniformly distributed along the streamwise and vertical directions behind shock wave front.

Numerical investigation of unsteady shedding behaviors of a reentrant jet supercavity

To investigate the unsteady shedding characteristics of a reentrant jet supercavity with a low Froude number, a high-fidelity numerical model based on the inhomogeneous multiphase model is developed to predict the complex supercavitation flow that occurs during supercavity development. The developed solver is validated quantitatively against experimental results in terms of supercavity geometry and closure mode. This study focuses on the initial generation and development process of a reentrant jet supercavity, revealing three distinct stages: foam cavity, transparent supercavity with rapid growth in dimensions, and fully developed supercavity exhibiting significant deformation. Owing to reverse flow of the gas–water mixture, interfacial instabilities arise from the unsteady cavity shedding, leading to fluctuations in supercavity shape. The types of large-scale cavity shedding observed in this work—wing-like and cloud-like—are caused by the concave deformation resulting from the reentrant jet. As the gas entrainment coefficient increases, the unsteady characteristics of pressure oscillation weaken, and the instance of wing-like cavities decreases. When the gas entrainment coefficient reaches a critical value, the twin-vortex closure mode occurs, resulting in a more stable flow behavior. In sum, we propose a theoretical model that elucidates the strength of the reentrant jet and reveals its unsteady shedding behavior during supercavity development.

Data-driven modal decomposition of R134a refrigerant cavitating flow in Venturi tube

This study utilized high-speed camera and large eddy simulation methods to explore the cavitating flow mechanisms and turbulence structures of R134a refrigerant inside a Venturi tube under varying cavitation numbers (CNs). Data-driven modal analysis approaches, proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), were introduced to identify and extract the energy hierarchy and transient characteristics within the cavitating flow. The analysis of grayscale images indicated that the cavitating flow gradually transitioned from quasi-periodic to unsteady flow as the CN decreased, and the severity of cavitation correlates with lower peak frequencies. The POD analysis facilitated the extraction of coherent structures in the cavity's temporal evolution, and the results indicate that the quasi-ordering shedding and collapse of large-scale cavity clouds predominantly occur under low cavitation intensity conditions. As the CN increases, the influence of small-scale cavity shedding becomes more significant. The first 30 most energetic modes occupied over 75% of the entire energy, and they were used to reconstruct the cavitating flow, achieving good consistency with transient flow snapshots. Additionally, the DMD results of the cavitating flow yield three frequency spans, including several prominent characteristic frequencies. These spans are closely linked to the cavity cloud structures of varying scales, unveiling the structural characteristics of unsteady cavitating flow.

Effect mechanisms of leading-edge tubercle on blade cavitation control in a waterjet pump

The bio-inspired leading-edge tubercles (LET) are specifically designed and exploited to control the blade cavitation dynamics under the inlet guide vans (IGVs) wake impacts in a waterjet pump. The experiments, numerical simulation, and modal analysis are jointly carried out to elaborate on the effects mechanisms and cavitation oscillations of the LET pump. It is observed that the tubercle blade cavitation is stably confined in the troughs with a tubular-like pattern and the spanwise coherent development is broken. The tubercles drive the flow turbulent and then form low pressure in the troughs to give rise to cavities. Weak counter-rotating vortex pairs can be identified in the tubercle trough. The analysis of vortex transportation demonstrates that vortex stretching and dilatation would be induced by tubercle cavitation. The loading instabilities obtained by Dynamic Mode Decomposition (DMD) indicate that the dominant oscillations emerge around the tubercles in the blade middle part regarding heavy loading. Due to the large-scale cavities depression by the tubercles, the thrust extremes in some revolutions could be efficiently avoided. In comparison with smooth and tubercle pumps, the thrust energy regarding the tonal and broadband frequency for a single blade and impeller are closing, which need to be further studied to degrade excited force instabilities. This work fundamentally investigates the cavitation instabilities and mechanisms in a tubercle waterjet pump, which could provide a guide on pump design to stabilize cavitation oscillations under uncertain inflow perturbations.

Multi-scale characteristics investigation of sheet/cloud cavitation

Sheet and cloud cavitation involve the formation of large-scale cavities and microbubbles across a wide range of length scales. In this study, a two-way coupling Eulerian-Lagrangian algorithm was utilized to simulate the cavitating flow around a NACA66 hydrofoil at an incidence of 8 degrees and a cavitation number of 1.2. The large eddy simulation (LES) and volume of fraction (VOF) methods are used to capture the large scale vapor structures in Eulerian frame. Meanwhile, the discrete bubble model (DBM) and simplified Rayleigh-Plesset equation are implied to solve the dynamic of Lagrangian microbubbles smaller than local grid scale. The results indicate that large-scale cavities are periodically shed downstream, influenced alternatively by the re-entrant jet and shock wave mechanisms, resulting in periodic variations of both the number and Sauter mean diameter of microscale bubbles. During the quasi-periodic evolution process of sheet/cloud cavitation, the microbubbles scatter around the large scale cavities where have strong turbulence intensity and high vorticity, and the probability density function of discrete bubble diameter similarly conforms to Gamma distribution with the dominant bubble size between 30 and 70μm. During the growth of an attached cavity, the number density of bubbles follows a power-law scaling with a value of -5/3 on radius. For the other stages, the bubble size spectrum of smaller microbubbles exhibits a -2/3 power-law scaling when the diameter of the microbubble is less than 200 μm. For larger bubbles with a diameter greater than 300 μm, the bubble density is proportional to the bubble radius to the power of -6.

Investigation of transient sheet/cloud cavitating flow dynamics from multiscale perspective

Sheet/cloud cavitation usually leads to a wide range of length scales in both turbulence and phase distribution from microbubbles to cavity advection. In the present work, the Eulerian–Lagrangian multiscale cavitation model with two-way coupling is utilized to simulate the cavitating flow around a (National Advisory Committee for Aeronautics) NACA66 hydrofoil at an incidence angle of 8° and a cavitation number of σ = 1.4. The model can simultaneously capture the large-scale cavities and the microscale bubbles. The cavitating flow features are in good agreement with the experimental observations containing not only the periodical formation, growth, detachment, and advection of large-scale cavities, but also thousands of microbubbles around the large-scale cavities. The results show that the overall evolution frequency in the flow is about 45 Hz. Meanwhile, the dynamic mode decomposition method is utilized to identify the large-scale coherent spatial and temporal features of the sheet/cloud cavitating flow, which indicates that complex vortices in various scales dominate the evolution of cavities in the corresponding scale, and the evolution frequency of large-scale vapor structure decreases with increasing the length scale of cavities. Under the effect of turbulence, the large-scale cavities break into microbubbles, causing the size and number of discrete bubbles to increase rapidly in the re-entrant jet and cloud shedding regions. Additionally, the bubble-size spectrum of the time-averaged distribution of a period in sheet/cloud cavitating flow has two size regimes. For larger bubbles, the bubble density is proportional to the bubble radius to the power of −10/3. The bubble size spectrum of smaller microbubbles exhibits a −4/3 power-law scaling.

Partial cavity shedding on a hydrofoil resulting from re-entrant flow and bubbly shock waves

Partial cavity flows forming on a NACA0015 hydrofoil are visualized using high-speed cinematography and time-resolved X-ray densitometry. These observations reveal the underlying flow features that lead to the cloud cavity shedding. Previous studies have reported that both near-surface liquid re-entrant flow and bubbly shock waves can serve as the mechanisms causing cavity pinch-off and cloud shedding. We identify both mechanisms in the current study. The cavity shedding frequency was also examined and related to the underlying flow dynamics. The probability of re-entrant flow or bubbly shock-induced shedding processes are quantified, and the likelihood of each mechanism is shown to be a function of both the cavitation number and the Mach number of the bubbly mixture within the separated region of the cavity. When the Mach number of the two-phase mixture in the cavity exceeds unity, shock waves become the dominant mechanism that lead to large-scale cavity shedding and cloud cavitation.

Mixed convection heat transfer and transient flow of high-pressure gas in a large-scale cavity with rotating blade

Mixed convection heat transfer phenomenon, incorporating natural and forced convection process, occurs widely in natural and industrial fields. Nevertheless, few works have investigated numerically the turbulent mixed convection heat transfer within the large-scale structure under high-pressure condition. In this study, a three-dimensional numerical model of a large-scale closed cavity with two rotating blades and reactor has been built on account of the finite volume method, aiming to explore the mixed convection heat transfer and turbulent flow of internal high-pressure gas. Compressible gas with varying thermophysical properties was chosen as the heat transfer medium and the numerical model was solved by Unsteady Reynolds-Averaged Navier-Stokes (URANS). Turbulent flow and heat transfer, inside the enclosure and reactor, were compared through the variation of the Reynolds number (Re), gas pressure (P) and heating surface temperature (Th). The results signify that for given P and Th, varying Re has a consistent impact on the transient flow and heat transfer process inside the enclosure and reactor. The turbulent flow and thermal transport are enhanced as increasing the Re. When the Re = 900,000, an enhanced forced convection effect is found inside the reactor. Dissimilar impacts on the flow field and thermal transport inside the enclosure and reactor are found with changing gas pressure owing to the interaction of natural and forced convection. The flow field attenuates gradually as the increment in P, and thereby larger high-temperature zone is achieved at a smaller pressure inside the enclosure, whilst inside the reactor, faster heat conduction is attained at a bigger pressure. Changing heating surface temperature has a more significant influence on the flow field and heat transfer inside the reactor compared to the enclosure. Additionally, increasing the Re and Th has a smaller effect on the average Nusselt number (Nuavg) while a positive correlation between the Nuavg and P is obtained.

Dynamics of cavity structures and wall-pressure fluctuations associated with shedding mechanism in unsteady sheet/cloud cavitating flows

The physics and mechanism of sheet/cloud cavitation in a convergent–divergent channel are investigated using synchronized dynamic surface pressure measurement and high-speed imaging in a water tunnel to probe the cavity shedding mechanism. Experiments are conducted at a fixed Reynolds number ofRe = 7.8 × 105for different values of the cavitation numberσbetween 1.20 and 0.65, ranging from intermittent inception cavitation, sheet cavitation to quasi-periodic cloud cavitation. Two distinct cloud cavitation regimes, i.e. the re-entrant jet and shockwave shedding mechanism, are observed, accompanied by complex flow phenomenon and dynamics, and are examined in detail. An increase in pressure fluctuation intensity at the numbers 3 and 4 transducer locations are captured during the transition from re-entrant jet to shockwave shedding mechanism. The spectral content analysis shows that, in cloud cavitation, several frequency peaks are identified with the dominant frequency caused by the large-scale cavity shedding process and the secondary frequency related to re-entrant jet/shockwave dynamics. Statistical analysis based on defined grey level profiles reveals that, in cloud cavitation, the double-peak behaviours of the probability density functions with negative skewness values are found to be owing to the interactions of the re-entrant jet/shockwave with cavities in the region of 0.25 ~ 0.65 mean cavity length (Lc). In addition, multi-scale proper orthogonal decomposition analysis with an emphasis on the flow structures in the region of 0.25 ~ 0.65Lcreveals that, under the shockwave shedding mechanism, both the re-entrant jet and shockwave are captured and their interactions are responsible for the dynamics and statistics of cloud shedding process.

Experimental study on the cavitation flow and motion characteristics of the vehicle launched underwater

In this paper, an experimental system was independently designed to investigate the cavitation flow mechanism and motion characteristic of the vehicle launched underwater. Conducted experiments based on high-speed photography, and the influence of cavity morphological evolution and kinematic characteristics with the different launch and transverse velocities were analyzed. The results show that cavity shedding phenomenon occurs on different scales. Subsequently, a wide range of pressure impulse on the surface of the vehicle is caused by the collapse of large-scale cavity groups, resulting in an obvious sputtering phenomenon on its surface during the water-exit stage. The more the launch speed increases, the longer the initial cavity length is. Moreover, the moment of completely shedding the cavity delays during the water exit process; Furthermore, with the increase of transverse speed, the attitude angle generally shows an increasing trend, but its growth rate slowed down during the large-scale shedding stage of the cavity.

Numerical Simulation on Hydrofracture Propagation in Fractured-Vuggy Unconventional Reservoirs

The unconventional reservoirs such as carbonate formation develops complex and diverse storage space structures, and it is composed of large-scale cavity, dissolved vug, and fractures. The carbonate reservoir is highly heterogeneous. Acid fracturing of carbonate reservoir is completed through the complex mechanical mechanism of interaction between vug and hydraulic fracture (HF). We use the equivalent method of reducing the rock strength by acid etching and serious fluid leakoff during interaction of HF and vug to establish a finite element (FE) model of HF propagation during acid fracturing in the fractured-vuggy carbonate reservoir. The model considers the effect of serious fluid leakoff during interaction between HF and vug, mechanism of interaction between HFs and the fracture-vug system, and change in acid etching intensity. Then, we carry out numerical simulation on impacts of injection rate, fluid viscosity, leakoff behavior in fractures and vugs, and natural fracture (NF) approaching angle on HF propagation in acid fracturing and compare the characteristics of injection pressure, fracture pressure, and HF size. It is suggested that the acid fracturing treatment should be operated by increasing the acid solution viscosity to reduce fluid leakoff, injecting fracturing fluid and acid fluid alternatively, increasing injection rate, and injecting fibers and ceramics when small pressure drop occurs during the HF interacts with the fracture-vug. When a large pressure drop occurs, it is suggested that the middle-low viscosity acid be injected at a low rate to etch the carbonate rock and enhance the fracture conductivity. HF propagates under higher pressure when the NF approaching angle is smaller.

Multiscale modeling of different cavitating flow patterns around NACA66 hydrofoil

The multiscale effect of cavitation is a complicated multiphase phenomenon involving macroscale cavities and microscale bubbles. The cavitating flows at four different patterns around a (National Advisory Committee for Aeronautics) NACA66 hydrofoil are simulated based on the multiscale model under the Eulerian–Lagrangian framework. The volume-of-fluid method is used to capture the transportation of large-scale cavities in the Eulerian framework, while small-scale bubbles smaller than the threshold value of computational cells are solved using the Lagrangian method and the simplified Rayleigh–Plesset equation. The turbulent flow is solved using the large-eddy simulation approach, and the two-way coupling source for momentum is calculated by integrating interacting forces of discrete bubbles. This work proposes a multiscale model to better investigate the vapor structure with an extensive range of length scales, and analyzes the evolution mechanism of vapor morphology and scale in different cavitation patterns first. The simulation results are compared with the experimental observations to verify the accuracy of the numerical method. Meanwhile, the results illustrate that the turbulence has a significant influence on the bubble behavior. With a decrease in cavitation number, the number and size of discrete bubbles increase significantly, and the probability density function of discrete bubble diameter similarly conforms to Gamma distribution at all cavitation patterns. For inception cavitation, sheet cavitation, and supercavitation, the shape of large-scale cavity is relatively stable, and the standard deviation of the number and Sauter mean diameter of microscale bubbles are much smaller than cloud cavitating flow. In contrast, the large-scale cavity sheds periodically in the cloud cavitating flow leading to the periodical variation of the number and the Sauter mean diameter of microscale bubbles as well. Additionally, the discrete bubbles are mainly distributed in the region with strong turbulence intensity and high vorticity.

Approaching the structure-property relationship of sintered metal nano/microparticles from the perspective of the agglomerate size effect

In this study, we explore the structure-property relationship of sintered metal nano/microparticles from the perspective of the agglomerate size effect. Through sintering experiments and mechanical tests of Cu particle pastes with different solvents, a linear correlation between the agglomerate size in the particle paste (La) and the size of large-scale cavities in the sintered structure (Lc) is revealed, and a negative correlation between the cavity size and the shear strength of the sintered structure is discovered. Based on these results, a quantitative model is proposed to predict the overall strength of the sintered structure (τf). A relationship τf = τc/(1 + √(2Lcmax/d)) is established, which fits the experimental results very well. The model reveals that the relative agglomerate size (La/d) or relative cavity size (Lc/d) plays a more important role than the particle size (d) itself in terms of defining the final sintering properties of metal nano/microparticles.

Data-driven modal decomposition of transient cavitating flow

The objective of this paper is to identify the dominant coherent structures within cavitating flow around a Clark-Y hydrofoil using two data-driven modal decomposition methods, proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD). A snapshot data sequence is obtained using a large eddy simulation and the interaction between cavitation and the vortex during cloud cavity shedding evolution is investigated. Modal decomposition via POD and DMD indicates that the dominant coherent structures include the large-scale cavity–vortex, re-entrant jet, shear layer, and small-scale vortex in the wake. In addition, the flow field can be reconstructed from the most energetic POD or DMD modes. The errors in the flow reconstructions produced using the first four POD modes, first eight POD modes, and first eight DMD modes are 3.884%, 3.240%, and 3.889%, respectively. Furthermore, transient cavitating flow can be predicted via the DMD method with an error of 8.081%. The largest errors in the reconstructed and predicted results occur mostly in the shear layer, trailing edge, and near wake. POD and DMD provide accurate and practically beneficial techniques for understanding cavitating flow, although substantial challenges remain with regard to predicting this intense nonlinear system.

Laser-Assisted Surface Modification of Ni Microstructures with Au and Pt toward Cell Biocompatibility and High Enzyme-Free Glucose Sensing.

We investigated the influence of morphology of Ni microstructures modified with Au and Pt on their cell biocompatibility and electrocatalytic activity toward non-enzymatic glucose detection. Synthesis and modification were carried out using a simple and inexpensive approach based on the method of laser-induced deposition of metal microstructures from a solution on the surface of various dielectrics. Morphological analysis of the fabricated materials demonstrated that the surface of the Ni electrode has a hierarchical structure with large-scale 10 μm pores and small-scale 10 nm irregularities. In turn, the Ni-Pt surface has large-scale cavities, small-scale pores (1–1.5 μm), and a few tens of nanometer particles opposite to Ni-Au that reveals no obvious hierarchical structure. These observations were supported by impedance spectroscopy confirming the hierarchy of the surface topography of Ni and Ni-Pt structures. We tested the biocompatibility of the fabricated Ni-based electrodes with the HeLa cells. It was shown that the Ni-Au electrode has a much better cell adhesion than Ni-Pt with a more complex morphology. On the contrary, porous Ni and Ni-Pt electrodes with a more developed surface area than that of Ni-Au have better catalytic performance toward enzymeless glucose sensing, revealing greater sensitivity, selectivity, and stability. In this regard, modification of Ni with Pt led to the most prominent results providing rather good glucose detection limits (0.14 and 0.19 μA) and linear ranges (10–300 and 300–1500 μA) as well as the highest sensitivities of 18,570 and 2929 μA mM–1 cm–2. We also proposed some ideas to clarify the observed behavior and explain the influence of morphology of the fabricated electrodes on their electrocatalytic activity and biocompatibility.

Multiscale modeling of tip-leakage cavitating flows by a combined volume of fluid and discrete bubble model

For the tip-leakage cavitating flow, the existence of both interface and microbubbles at scales separated by orders of magnitude makes it difficult to be comprehensively reproduced by numerical modeling. This work aims to develop a multiscale model that directly resolves the large-scale cavities and models small discrete bubbles. The volume of fluid (VOF) method and the Schnerr–Sauer cavitation model are first adopted to represent the phase field of water and vapor from a macroscale point of view. A discrete bubble model (DBM) based on the Lagrangian formulation is then developed to simulate the microscale cavitation bubbles that are smoothed in the macroscale model due to the limited mesh resolution. The transition between DBM and VOF is also implemented to achieve the multiscale simulation. For modeling of the turbulence, the scale adaptive simulation approach is used. The tip-leakage cavitating flows induced by the NACA0009 hydrofoil under the conditions with different gaps according to the reported experiment are simulated. Results show that, using the proposed multiscale model, better agreements can be obtained compared with the macroscale model, and specific phenomena can be well revealed including the bubble nucleation, growth and collapse, the interaction between discrete bubbles and large-scale cavities.

Numerical pressure transient analysis for unfilled-caved carbonate reservoirs based on Stokes-Darcy coupled theory

Caved carbonate reservoirs are very special because of the strong heterogeneity. The pressure transient behavior of the caved carbonate reservoirs is quite different from the conventional homogeneous or dual medium reservoirs because of the presence of large-scale cavities. There are two types of cavities: filled and unfilled, which dominated the production of the reservoirs. Fluid flow in the unfilled cavity should be described by Stokes' equation rather than Darcy's law. It is needed to better understand the role of the unfilled cavities plays in the pressure transient analysis. The objective of this work is to analyze the pressure transient behavior of the unfilled cavities. A coupled Stokes-Darcy pressure transient model is developed and the finite element method is applied in the solutions of the mathematical models. Then, the numerical pressure transient model is used in the analysis of two typical cases: a well drilled into the unfilled cavity (WIC) and a well not drilled into the unfilled cavity (WOC). The type curves of the WIC model indicate that flow in the unfilled cavity is an oscillated pressure-drop rather than a radial flow. The unfilled cavity that the well drilled into would be considered as an enlarged wellbore which is equivalent to a negative skin factor, as a consequence the wellbore storage coefficient will increase. Main characteristics of type curves for WOC model are the valley on the pressure derivative. A cavity with a larger size and smaller distance from the wellbore would give rise to a deeper valley. Comparative results indicate that unfilled cavities described by the Stokes' equation are not the limit of the filled cavities with extremely large mobility, which was predicted by previous work.

Experimental and numerical study of the cavitation surge passive control around a semi-circular leading-edge flat plate

In this paper, we performed the numerical and experimental study of unsteady cavitation surge around a semi-circular leading-edge flat plate using a passive flow control method. We mounted a miniature spanwise wedge-type vortex generator on the suction side of the model close to its leading edge. To mitigate the destructive impact of this type of cavitation on the hydrofoil performance, we analyzed the effects of the passive control on the dynamics of cavitation surge. First, we investigated experimentally the unsteady cavitating flow around the semi-circular leading-edge flat plate without passive control using high-speed visualization, acoustic measurements and particle image velocimetry method. Next, we simulated numerically the dynamics of unsteady flow under the cavitation surge conditions with an open source code and validated the numerical results using the experimental data. We used a proper interaction between turbulence and cavitation model to capture a highly unsteady behavior of cavitation surge. Finally, we considered the effects of the passive control device on the mechanism of the cavitation surge instability. Our results revealed that using the passive control method, it is possible to stabilize the attached cavity on the suction side of the flat plate, to hinder the development of the spanwise instability of the attached cavity and to mitigate large-scale cavity structures. Furthermore, high-pressure pulsations in the wake region induced by unsteady cavitation surge were considerably reduced.

Lattice Boltzmann modeling of convective flows in a large-scale cavity heated from below by two imposed temperature profiles

PurposeThe purpose of this paper is to model the convective flows in a room equipped by a glass door and a heated floor of length l = 0.8 × H and submitted to a sinusoidal temperature profile and mono alternative temperature profile.Design/methodology/approachThe paper opts for a numerical study of convective flows in a large scale cavity using the Lattice Boltzmann Method (LBM) by considering a two dimensions (2D) square cavity of side H and filled by air (Pr = 0.71). All the vertical walls, the ceiling and the rest of the floor are thermally insulated, the hot portion of length l = 0.8×H is heated with two imposed temperature profiles of amplitude values 0.2 ≤ a ≤ 0.6 and for two different periods ζ = ζ0 and ζ = 0.4×ζ0. One of the vertical walls has a cold portion θc = 0 that represents the glass door.FindingsA systematic study of the flow structure and heat transfer is carried out considering principal control parameters: amplitude “a” and period ζ for Rayleigh number Ra = 108. Effects of these parameters on results are presented in terms of isotherms, streamlines, profiles of velocities, temperature in the cavity, global and local Nusselt number. It has been found that an increase in amplitude or period increases the amplitude of the temperature in the core of cavity. The Nusselt number increases when the amplitude “a” of the imposed temperature increases, but this later is not affected by variation of the period.Originality/valueThe authors used LBM to simulate the convective flows in a cavity at high Ra, heated from below by tow imposed temperature profiles. Indeed, they simulate a local equipped by a solar water heater (SWH). The floor is subjected to a periodic heating: Sinusoidal heating (Case 1) for which the temperature varies sinusoidally (SWH without a supplement), and mono alternation heating (Case 2), the temperature evolves like a redressed signal (SWH with a supplement). The considered method has been successfully validated and compared with the previous work. The study has been conducted using several control parameters such as the signal amplitude and period in the case of turbulent convection. This allowed us to obtain a considerable set of results that can be used for engineering.