scholarly journals Effects of Wavy Leading-Edge Protuberance on Hydrofoil Performance and Its Flow Mechanism

2021 ◽  
Vol 9 (10) ◽  
pp. 1138
Author(s):  
Jing Li ◽  
Chunbao Liu ◽  
Xiaoying Li
Keyword(s):  
Flow Instability ◽  
Three Dimensional ◽  
Leading Edge ◽  
Streamwise Vortex ◽  
Cavitating Flow ◽  
Cavitation Inception ◽  
Vortex Interactions ◽  
Cavitation Pressure ◽  
Les Model ◽  
Unsteady Cavitating Flow

This paper examines the effects on a Clark-y three-dimensional hydrofoil of wavy leading-edge protuberances in a quantitative and qualitative way. The simulation is accompanied by a hybrid RANS-LES model in conjunction with Zwart-Gerber–Belamri model. Detailed discussions of the stable no-cavitating, unsteady cavitating flow fields and the control mechanics are involved. The force characteristics, complicated flow behaviors, cavitation–streamwise vortex interactions, and the cavitating flow instability are all presented. The results demonstrate that protuberances acting as vortex generators produce a continuous influx of boundary-layer vorticity, significantly enhancing the momentum transfer of streamwise vortices and therefore improving the hydrodynamics of the hydrofoil. Significant interactions are described, including the encouragement impact of cavitation evolution on the fragmentation of streamwise vorticities as well as the compartmentation effect of streamwise vorticities binding the cavitation inception inside the troughs. The variations in cavitation pressure are mainly due to the acceleration in steam volume. In summary, it is vital for new hydrofoils or propeller designs to understand in depth the effects of leading-edge protuberances on flow control.

Lagrangian Analysis of Unsteady Partial Cavitating Flow Around a Three-Dimensional Hydrofoil

2020 ◽  
Author(s):  
Tingyun Yin ◽  
Giorgio Pavesi ◽  
Ji Pei ◽  
Shouqi Yuan ◽  
Giovanna Cavazzini ◽  
...  
Keyword(s):  
Coherent Structure ◽  
Cavity Growth ◽  
Three Dimensional ◽  
Adverse Pressure Gradient ◽  
Buffer Zone ◽  
Cavitating Flow ◽  
Lagrangian Analysis ◽  
Lagrangian Coherent Structure ◽  
Cavity Development ◽  
Unsteady Cavitating Flow

Abstract This study employs an incompressible homogeneous flow framework with a transport-equation-based cavitation model and shear stress transport turbulence model to successfully reproduce the unsteady cavitating flow around a three-dimensional hydrofoil. Cavity growth, development, and break-off during the periodic shedding process are adequately reproduced and match experimental observations. The predicted shedding frequency is very close to the experimental value of 23 ms. By monitoring the motions of the seeding trackers, growth-up of attached cavity and dynamic evolution of U-type cavity are clearly displayed, which indicating the trackers could serve as an effective tool to visualize the cavitating field. Repelling Lagrangian Coherent Structure (RLCS) is so complex that abundant flow patterns are highlighted, reflecting the intricacy of cavity development. The formation of cloud cavities is clearly characterized by the Attracting Lagrangian Coherent Structure (ALCS), where bumbling wave wrapping the whole shedding cavities indicates the rotating transform of cavities and stretching of the wave eyes shows the distortion of vortices. Generation of the re-entrant jet is considered to be not only associated with the adverse pressure gradient due to the positive attack angle, but also the contribution of cloud cavitating flow, based on the observation of a buffer zone between the attached and cloud cavities.

Numerical investigation of unsteady cavitating turbulent flows around a three-dimensional hydrofoil using stress-blended eddy simulation

2021 ◽  
pp. 095440892110251
Author(s):  
Jing Li ◽  
Chunbao Liu ◽  
Zilin Ran ◽  
Bosen Chai
Keyword(s):  
Numerical Investigation ◽  
Turbulent Flows ◽  
Large Scale ◽  
Flow Instability ◽  
Cavity Growth ◽  
Hybrid Approach ◽  
Three Dimensional ◽  
Cavitating Flow ◽  
Rans Model ◽  
Eddy Simulation

The mechanism of flow instability, which involves complex gas–liquid interactions and multiscale vortical structures, is one of the hot research areas in cavitating flow. The role of turbulence modeling is crucial in the numerical investigation of unsteady flow characteristics. Although large-eddy simulation (LES) has been used as a reliable numerical method, it is computationally costly. In this work, we used a hybrid Reynolds-averaged Navier–Stokes (RANS) and LES model, that is, stress-blended eddy simulation (SBES), to improve the prediction capability for the cloud cavitating flow. Our hybrid approach introduces a shielding function to integrate the RANS model with the LES applied only regionally, such as to large-scale separated flow regions. The results showed that the periodic shedding of cavity growth, break off, and collapse around a three-dimensional Clark-Y hydrofoil was reproduced in accordance with experimental observations. The lift/drag coefficients, streamwise velocity profiles, and cavity patterns obtained by the SBES model were in better agreement with the experimental data than those obtained by the modified RANS model. The re-entrant jet dynamics responsible for the break off of the attached cavity were discussed. Further analysis of vorticity transportation indicated that the stretching and dilatation terms dominated the development of vorticity around the hydrofoil. In conclusion, the SBES model can be used to predict cavitating turbulent flows in practical engineering applications.

Numerical and Experimental Investigations of Cavitating Flow in a Vertical Multi-Hole Injector Nozzle

2010 ◽  
Author(s):  
Zhixia He ◽  
Jing Bai ◽  
Qian Wang ◽  
Qingmu Mu ◽  
Yunlong Huang
Keyword(s):  
Numerical Simulation ◽  
Numerical Models ◽  
Three Dimensional ◽  
Injection Pressure ◽  
Cavitating Flow ◽  
Critical Conditions ◽  
Experimental Investigations ◽  
Nozzle Flow ◽  
Cavitation Inception ◽  
Injector Nozzle

The presence of cavitation and turbulence in a diesel injector nozzle has significant effect on the subsequent spray characteristics. However, the mechanism of the cavitating flow and its effect on the subsequent spray is unclear because of the complexities of the nozzle flow, such as the cavitation phenomena and turbulence. A flow visualization experiment system with a transparent scaled-up vertical multi-hole injector nozzle tip was setup for getting the experimental data to make a comparison to validate the calculated results from the three dimensional numerical simulation of cavitating flow in the nozzle with mixture multi-phase cavitating flow model and good qualitative agreement was seen between the two sets of data. The critical conditions for cavitation inception were derived as well as the relationship between the discharge coefficient and non-dimensional cavitation parameter. After wards, the testified numerical models were used to analyze the effects of injection pressure, back pressure, cavitation parameter, Reynolds number, injector needle lift and needle eccentricity on the cavitating flow inside the nozzle. Combined with visual experimental results, numerical simulation results can clearly reveal the three-dimensional nature of the nozzle flow and the location and shape of the cavitation induced vapor distribution, which can help understand the nozzle flow better and eventually put forward the optimization ideas of diesel injectors.

scholarly journals Numerical prediction of cavitating flow around a hydrofoil using pans and improved shear stress transport k-omega model

2015 ◽  
Vol 19 (4) ◽  
pp. 1211-1216 ◽  
Author(s):  
De-Sheng Zhang ◽  
Da-Zhi Pan ◽  
Hai-Yu Wang ◽  
Wei-Dong Shi
Keyword(s):  
Shear Stress ◽  
Turbulence Models ◽  
Vortex Pair ◽  
Cavitating Flow ◽  
Numerical Prediction ◽  
Navier Stokes ◽  
Cavitation Inception ◽  
Shear Stress Transport ◽  
Omega Model ◽  
Unsteady Cavitating Flow

The prediction accuracies of partially-averaged Navier-Stokes model and improved shear stress transport k-? turbulence model for simulating the unsteady cavitating flow around the hydrofoil were discussed in this paper. Numerical results show that the two turbulence models can effectively reproduce the cavitation evolution process. The numerical prediction for the cycle time of cavitation inception, development, detachment, and collapse agrees well with the experimental data. It is found that the vortex pair induced by the interaction between the re-entrant jet and mainstream is responsible for the instability of the cavitation shedding flow.

Unsteady Vortex Interactions for Performance Enhancement of a Free Flying Dragonfly

2017 ◽  
Author(s):  
Csaba Hefler ◽  
Ryusuke Noda ◽  
Wei Shyy ◽  
Huihe Qiu
Keyword(s):  
High Speed ◽  
Performance Enhancement ◽  
Hind Wing ◽  
Three Dimensional ◽  
Leading Edge ◽  
The Body ◽  
Valuable Insight ◽  
Time Resolved ◽  
Flight Chamber ◽  
Vortex Interactions

Bioinspired designs offer a viable solution to the design challenges of micro air vehicles (MAVs) desired to operate in the same size region under similar conditions as flying vertebrates and insects. Inspired by our previous studies of tethered live dragonflies, here, a quantitative characterization of the unsteady aerodynamic features of a live, freely flying dragonfly under well-established level flight condition will be presented. In particular with regard of the span-wise features of vortex interactions between the fore- and hind-pairs of wings, that highly contributes to the flight agility and efficiency of dragonflies. Flow fields of free flying dragonflies in still air have been measured by time-resolved stereo particle image velocimetry (TRS_PIV). A specifically designed dark flight chamber has been built, where hand hold dragonflies (Pantala flavescens) were released and made to fly nearly parallel to the measurement plane toward a guiding light. Realistic kinematics of the dragonfly wings in free flight were measured by filming with 2 synchronized high-speed video cameras. Using the recorded images, several dozens of landmarks on the fore- and hind-wing surfaces and several landmarks on the body were traced with high precision and the three-dimensional coordinates were then reconstructed with a direct linear transformation (DLT) method. Using the reconstructed wing-body model, Navier-Stokes-based computational fluid dynamics (CFD) analyses, with wing shapes prescribed based on the experimental measurement, dynamically moving multi blocked, and an overset-grid system were conducted. The numerical results are in overall agreement with the PIV data, and the combined numerical and experimental approach offers valuable insight into aerodynamic analyses. The results show that the interaction with the forewing leading edge vortex (LEV) strongly influences the flow structures around the inner spanwise region of the hindwing, while aerodynamic enhancement via vortex capture in the outer span is observed. The interaction depends not solely on wing phasing, geometrical arrangement, but also the flight mission.

Discrete Bubble Modeling of Unsteady Cavitating Flow

2006 ◽  
Vol 4 (5-6) ◽  
pp. 601-616 ◽  
Author(s):  
Zhiliang Xu ◽  
Myoungnyoun Kim ◽  
Tianshi Lu ◽  
Wonho Oh ◽  
James Glimm ◽  
...  
Keyword(s):  
Cavitating Flow ◽  
Unsteady Cavitating Flow
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