Hyaluronic acid (HA) exists naturally as an important component of the extracellular matrix (ECM) in the human body. In recent decades, HA has been widely used in bone regeneration, and is currently ...a popular topic, particularly in the craniofacial and dental fields. From maxilla augmentation to craniofacial bone trauma, there is now a large demand for bone regenerative therapy. Serving as a cell-seeding scaffold or a carrier for bioactive components, hyaluronic acid-incorporated scaffolds and carriers in bone regeneration can be fabricated into either rigid or colloidal forms. Since the type of material used is a critical factor in the biological properties of a scaffold, HA derivatives or HA-incorporated composite scaffolds have shown excellent potential for improving osteogenesis and mineralization. Furthermore, in order to better enhance osteogenesis, local delivery carriers based on hyaluronic acid derivatives, rather than specifically serving as scaffolds, can be established by loading different osteoinductive or osteogenetic components and acquiring different release patterns. Such osteoinductive carriers immobilized on implant surfaces are also effective in improving osseointegration. Thus, as such a competent biomaterial, hyaluronic acid should be considered a promising tool in bone regeneration.
► Cavitating flow around a twisted hydrofoil is studied by PANS method. ► Evolution of cavitation patterns are well predicted compared to experiments. ► The reasons for the primary and secondary ...shedding are discussed. ► The mechanism of cavitating horse-shoe vortex production is illustrated.
Cavitating turbulent flow around hydrofoils was simulated using the Partially-Averaged Navier–Stokes (PANS) method and a mass transfer cavitation model with the maximum density ratio (ρl/ρv,clip) effect between the liquid and the vapor. The predicted cavity length and thickness of stable cavities as well as the pressure distribution along the suction surface of a NACA66(MOD) hydrofoil compare well with experimental data when using the actual maximum density ratio (ρl/ρv,clip=43391) at room temperature. The unsteady cavitation patterns and their evolution around a Delft twisted hydrofoil were then simulated. The numerical results indicate that the cavity volume fluctuates dramatically as the cavitating flow develops with cavity growth, destabilization, and collapse. The predicted three dimensional cavity structures due to the variation of attack angle in the span-wise direction and the shedding cycle as well as its frequency agree fairly well with experimental observations. The distinct side-lobes of the attached cavity and the shedding U-shaped horse-shoe vortex are well captured. Furthermore, it is shown that the shedding horse-shoe vortex includes a primary U-shaped vapor cloud and two secondary U-shaped vapor clouds originating from the primary shedding at the cavity center and the secondary shedding at both cavity sides. The primary shedding is related to the collision of a radially-diverging re-entrant jet and the attached cavity surface, while the secondary shedding is due to the collision of side-entrant jets and the radially-diverging re-entrant jet. The local flow fields show that the interaction between the circulating flow and the shedding vapor cloud may be the main mechanism producing the cavitating horse-shoe vortex. Two side views described by iso-surfaces of the vapor volume fraction for a 10% vapor volume, and a non-dimensional Q-criterion equal to 200 are used to illustrate the formation, roll-up and transport of the shedding horse-shoe vortex. The predicted height of the shedding horse-shoe vortex increases as the vortex moves downstream. It is shown that the shape of the horse-shoe vortex for the non-dimensional Q-criterion is more complicated than that of the 10% vapor fraction iso-surface and is more consistent with the experiments. Further, though the time-averaged lift coefficient predicted by the PANS calculation is about 12% lower than the experimental value, it is better than other predictions based on RANS solvers.
Compared to non-cavitating flow, cavitating flow is much complex owing to the numerical difficulties caused by cavity generation and collapse. In this paper, the cavitating flow around a NACA66 ...hydrofoil is studied numerically with particular emphasis on understanding the cavitation structures and the shedding dynamics. Large Eddy Simulation (LES) was coupled with a homogeneous cavitation model to calculate the pressure, velocity, vapor volume fraction and vorticity around the hydrofoil. The predicted cavitation shedding dynamics behavior, including the cavity growth, break-off and collapse downstream, agrees fairly well with experiment. Some fundamental issues such as the transition of a cavitating flow structure from 2D to 3D associated with cavitation-vortex interaction are discussed using the vorticity transport equation for variable density flow. A simplified one-dimensional model for the present configuration is adopted and calibrated against the LES results to better clarify the physical mechanism for the cavitation induced pressure fluctuations. The results verify the relationship between pressure fluctuations and the cavity shedding process (e.g. the variations of the flow rate and cavity volume) and demonstrate that the cavity volume acceleration is the main source of the pressure fluctuations around the cavitating hydrofoil. This research provides a better understanding of the mechanism driving the cavitation excited pressure pulsations, which will facilitate development of engineering designs to control these vibrations.
In the present paper, a new control method for tip-leakage vortex (TLV) cavitation is proposed. This method, which combines the effects of grooves and winglets, is made of overhanging grooves (OHGs) ...fitted at the tip of a hydrofoil. Experimental and numerical investigations are conducted to evaluate the performances of OHGs in terms of TLV cavitation suppression. The results are systematically compared with the baseline, conventional grooves (CGs) and anti-cavitation lip (ACL) and a significant improvement of TLV cavitation suppression is obtained with the OHGs. We also carried out a primary optimization design of the OHGs and a more effective suppression on TLV cavitation is obtained for small gaps and TLV cavitation is almost suppressed for middle and large gaps. The underlying reasons for TLV cavitation mitigation are discussed in detail with the help of numerical simulations. It indicates that for small gap sizes, OHGs can effectively weaken the strength of both TLV and tip-separation vortex (TSV) and mitigate TLV cavitation. For middle and large gap sizes, it is found that OHGs will induce an increase in the TLV core size, which further increases local minimum pressure. The influence of OHGs on the performance of hydrofoil is also examined, which indicates that the fluctuation of TLV cavitation can be effectively suppressed by OHGs and no significant alteration of time-averaged drag and lift is induced by OHGs. Our work shows that the OHGs can effectively suppress TLV cavitation with limited influence on the performances of hydrofoil in a large range of the gap sizes, which is a promising method for the control of TLV cavitation in hydraulic machinery.
Graphic abstract
► Cavitating flow around propellers in non-uniform wake is studied. ► Evolution of cavitation and pressure fluctuation are predicted well compared to experiments. ► The relationship of cavity volume ...and pressure fluctuation is discussed. ► The physical mechanism of excited pressure by cavitation is illustrated.
Unsteady cavitating turbulent flows around a conventional marine propeller in a non-uniform wake were analyzed to predict the excited pressure fluctuations. The numerical simulations of the propeller cavitation were based on the Navier–Stokes equations solved with a mass transfer cavitation model, the k–ω SST turbulence model and a sliding mesh. The evolution of the unsteady cavitation and the pressure fluctuations around the propeller in the non-uniform flow are predicted fairly well compared to experimental results. The CFD results verify the connection between the pressure fluctuations and the changing cavitation patterns as the blades sweep through the high velocity wake region. Furthermore, to better demonstrate the physical mechanism of the cavity-generated pressure field, the cavity volume was calculated and analyzed to illustrate the relationship between the cavity evolution and the pressure fluctuations. The analysis shows that the acceleration due to the cavity volume changes is the main source of the pressure fluctuations excited by the propeller cavitation. These results demonstrate that this numerical methodology is suitable for simulating unsteady cavitating flows around a propeller.
Volumetric measurement for the non-cavitating tip vortex in the near field of an elliptical hydrofoil is conducted using tomographic particle image velocimetry, which provides a fully ...three-dimensional diagnose of the vortex formation and development. The wandering motion and flow properties of the near-field tip vortex under different incident angles and Reynolds numbers are investigated in detail. Unlike in the far field, the wandering motion in the near field is mainly subject to the local flow unsteadiness rather than the flow condition. By the “re-centered” post-processing, the deviations introduced by the wandering motion can be technically corrected, and more accurate vortex properties can be thus obtained. In the near field, a turning point of the vortex center trajectory is detected, the position of which is basically independent of the flow condition. By investigating the local flow properties, it is found that this turning point is the position where the tip vortex completely leaves the trailing edge of hydrofoil and enters the wake region. At this turning point, the external supply to the vortex core starts to be restricted, and the vortex circulation reaches a rather constant value. Further according to the local flow properties, the development process of the near-field tip vortex can be divided into three stages: vortex-attached stage, vortex-lifting stage and vortex-detached stage, which are found to be closely relevant to the hydrofoil configuration.
Unsteady cavitating turbulent flow simulations need to be responsible for both cavitation and turbulence modeling issues. The Partially-Averaged Navier–Stokes (PANS) computational model developed ...from the RANS method and the k–ε turbulence model are used to model turbulent cavitating flow with a mass transfer cavitation model in the present paper. An objective of this study is to pursue more accurate estimates of unsteady cavitating flows with large-scale fluctuations at a reasonable cost. Firstly, the unsteady cavitating flow simulations over a NACA66-mod hydrofoil are performed using the PANS method with various values of the resolution control parameters (fk=1∼0.2, fε=1) to evaluate the numerical methods based on experimental data. The comparison with the experiments show that the numerical analysis with a fk=0.2 can predict the cavity evolution and shedding frequency fairly well. Then, cavitating flow around a marine propeller in non-uniform wake was simulated by PANS method. The calculations show that large cavity volume pulsation as the blade passes through the wake region is resolved better by the PANS method with fk=0.2 than by the RANS method with the k–ε or k–ω SST turbulence models. This can be contributed to the fact that a smaller fk give larger cavity volume pulsations leading to increased cavity volume accelerations and larger pressure fluctuations above the propeller, while a larger fk overestimates the turbulent viscosity along the rear part of the cavity. Finally, it is confirmed from the simulation by the PANS method with fk=0.2 that the whole process of cavitating flow evolution around the propeller in non-uniform wake can be very well reproduced including cavitation inception, sheet cavitation and tip vortex cavitation observed experimentally.
•The cavitating flow around a tip vortex is simulated with LES.•The reason for the discrepancy between the predicted and observed TVC is discussed.•An Euler-Lagrangian cavitation model is proposed to ...improve the accuracy of TVC.
Numerical simulation of tip vortex cavitation (TVC) remains a challenging task in a variety of applications, such as axial turbines and pumps as well as marine propellers. Although it is well known that TVC is highly sensitive to gas content, be it dissolved or not, numerical models do not consider this aspect so far. As a result, numerical simulations usually underestimate the development or the intensity of TVC. In the present paper, we propose an new Euler-Lagrangian cavitation model based on Rayleigh-Plesset (R-P) equation, taking into account the non-condensable gas. In this model, the Euler method is used to solve the global flow field and the Lagrangian method is used to track the migration of non-condensable gas bubbles into the vortex core. Based on the simplified R-P equation, the connection between local gas concentration and its effect on cavitation is modeled and the mass source terms in the original Schnerr-Sauer (S-S) cavitation model are modified. We applied the new cavitation model to a simplified case study, made of an elliptical NACA-16020 hydrofoil and compared the results with experimental observation. We obtained a significant improvement of the TVC prediction. Our work illustrates the major role of the gas content in sustaining cavitation downstream of the hydrofoil through an efficient attraction of nuclei, fueled by the low pressure induced by the vortex flow.
The present paper focuses on the numerical simulation of unsteady cavitation around a NACA66 hydrofoil to improve the understanding of the cavitation effects on hydraulic machinery. For this aim, the ...Zwart–Gerber–Belamri cavitation model was updated and uploaded as a library file for OpenFOAM’s solvers using C++ language. Furthermore, the hybrid Reynold average Navier–Stokes (RANS)–large eddy simulation (LES) model k - ω SST scale adaptive simulation (SAS) was implemented as a turbulence model for the present study of scale adaptive simulation. For validation, numerical results were compared with experimental results obtained by Leroux at the Naval Academy Research Institute in France. In order to highlight the benefits in terms of computational consumption and reproduction of the phenomenon the k - ω SST SAS model was compared against implicit large eddy simulation (ILES). Results show that the cavitation evolution including the maximum vapor length, the detachment and the oscillation frequency were reproduced satisfactorily using k - ω SST SAS. Moreover, k - ω SST SAS results predicted a lower total vapor volume on time than ILES, which is related to observed pulses of pressure coefficient, C p , and those match fairly well with the experimental results. To summarize, the k - ω SST SAS model predicts with good accuracy unsteady cavitation behavior around hydrofoils and shows improved versatility over the ILES approach.
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