Search results
1 – 8 of 8Włodzimierz Wróblewski, Krzysztof Bochon, Mirosław Majkut, Krzysztof Rusin and Emad Hasani Malekshah
The presence of air in the water flow over the hydrofoil is investigated. The examined hydrofoil is ClarkY 11.7% with an angle of attack of 8 deg. The flow simulations are…
Abstract
Purpose
The presence of air in the water flow over the hydrofoil is investigated. The examined hydrofoil is ClarkY 11.7% with an angle of attack of 8 deg. The flow simulations are performed with the assumption of different models. The Singhal cavitation model and the models which resolve the non-condensable gas including 2phases and 3phases are implemented in the numerical model. The calculations are performed with the uRANS model with assumption of the constant temperature of the mixture. The two-phase flow is simulated with a mixture model. The dynamics and structures of cavities are compared with literature data and experimental results.
Design/methodology/approach
The cavitation regime can be observed in some working conditions of turbomachines. The phase transition, which appears on the blades, is the source of high dynamic forces, noise and also can lead to the intensive erosion of the blade surfaces. The need to control this process and to prevent or reduce the undesirable effects can be fulfilled by the application of non-condensable gases to the liquid.
Findings
The results show that the Singhal cavitation model predicts the cavity structure and related characteristics differently with 2phases and 3phases models at low cavitation number where the cavitating flow is highly dynamic. On the other hand, the impact of dissolved air on the cloud structure and dynamic characteristic of cavitating flow is gently observable.
Originality/value
The originality of this paper is the evaluation of different numerical cavitation models for the prediction of dynamic characteristics of cavitating flow in the presence of air.
Details
Keywords
Cheng Liu, Qingdong Yan and Houston G. Wood
The purpose of this paper is to study the mechanism and suppression of instabilities induced by cavitating flow around a three-dimensional hydrofoil with a particular focus on…
Abstract
Purpose
The purpose of this paper is to study the mechanism and suppression of instabilities induced by cavitating flow around a three-dimensional hydrofoil with a particular focus on cavitation control with a slot.
Design/methodology/approach
The transient cavitating flow around a Clark-Y hydrofoil was investigated using a transport-equation-based cavitation model and the stress-blended eddy simulation model was used to capture the flow turbulence. A homogeneous Rayleigh–Plesset cavitation model was used to model the transient cavitation process and the results were validated with test data. A slot was applied to the hydrofoil to suppress cavitation instabilities, and various slot widths and exit locations were applied to the blade and the cavitation behavior, as well as drag/lift forces, were simulated and compared to investigate the effects of slot geometries on cavitation suppression.
Findings
The large eddy simulation based turbulence model was able to capture the interactions between the cavitation and turbulence. Moreover, the simulation revealed that the re-entrant jet was responsible for the periodic shedding of cavities. The results indicated that a slot was able to mitigate or even suppress cavitation-induced instabilities. A jet flow was generated at the slot exit and disturbed the re-entrant jet. If the slot geometry was properly designed, the jet could block the re-entrant jet and suppress the unsteady cavitation behavior.
Originality/value
This study provides unique insights into the complicated transient cavitation flows around a three-dimensional hydrofoil and introduces an effective passive cavitation control technique useful to researchers and engineers in the areas of fluid dynamics and turbomachinery.
Details
Keywords
The purpose of this paper is to use the NACA 0015 symmetric hydrofoil as the research subject and control cloud cavitation on hydrofoils.
Abstract
Purpose
The purpose of this paper is to use the NACA 0015 symmetric hydrofoil as the research subject and control cloud cavitation on hydrofoils.
Design/methodology/approach
Based on observed distribution of caudal fin spines on fish, a bionic structure of fin-like spines is arranged on the hydrofoil suction surface, which maintains the cavitation in a quasi-steady state stage by eliminating the cyclic shedding process of cloud cavitation. Based on the modified shear stress transport k-ω turbulence model and the Zwart–Gerber–Belamri cavitation model, this paper compares and analyzes the NACA 0015 hydrofoil and the bionic NACA 0015 hydrofoil under condition of an angle of attack of 8° and a cavitation number of 0.8.
Findings
The results show that the average drag of the hydrofoil is reduced but the lift is decreased, and the lift-drag ratio is increased after arranging the bionic structure. The bionic structure can effectively reduce the turbulent kinetic energy and make the flow more stable; it also can effectively control the hydrofoil surface side-entrant jet and the vortex shedding process of the near wall region.
Originality/value
Based on the above conclusions, the bionic structure of fin-like spines can achieve a significant passive control in the hydrofoil cloud cavitation process.
Details
Keywords
Yu Zhao, Guoyu Wang and Biao Huang
The purpose of this paper is to assess the predictive capability of the streamline curvature correction model (CCM) and investigate the unsteady vortex behavior of the cloud…
Abstract
Purpose
The purpose of this paper is to assess the predictive capability of the streamline curvature correction model (CCM) and investigate the unsteady vortex behavior of the cloud cavitating flows around a hydrofoil.
Design/methodology/approach
The design of the paper is based on introducing the curvature correction method to the original k-ε model. Calculations of unsteady cloud cavitating flows around a Clark-Y hydrofoil are performed using both the CCM and the baseline model.
Findings
Compared with the baseline model, better agreements are observed between the predictions of the CCM model and experimental data, especially the cavity shedding process. Based on the computations, it is demonstrated that streamline curvature correction of the CCM model can effectively decrease predicted turbulence kinetic energy and eddy viscosity in cavity shedding region. This leads to the better prediction for the recirculation zone located downstream of the attached cavity, and dynamics of this recirculation zone contribute to the formation and development of the re-entrant jet.
Originality/value
The authors apply streamline curvature correction to the calculations of unsteady cloud cavitating flows and discuss the interactions between the cavitation unsteadiness and vortex structures to get an insight of the correction mechanics.
Details
Keywords
Tom Schultheiss, Lorraine Hartline, Jean Mandeberg, Pam Petrich and Sue Stern
The following classified, annotated list of titles is intended to provide reference librarians with a current checklist of new reference books, and is designed to supplement the…
Abstract
The following classified, annotated list of titles is intended to provide reference librarians with a current checklist of new reference books, and is designed to supplement the RSR review column, “Recent Reference Books,” by Frances Neel Cheney. “Reference Books in Print” includes all additional books received prior to the inclusion deadline established for this issue. Appearance in this column does not preclude a later review in RSR. Publishers are urged to send a copy of all new reference books directly to RSR as soon as published, for immediate listing in “Reference Books in Print.” Reference books with imprints older than two years will not be included (with the exception of current reprints or older books newly acquired for distribution by another publisher). The column shall also occasionally include library science or other library related publications of other than a reference character.
Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States…
Abstract
Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued.
The following classified, annotated list of titles is intended to provide reference librarians with a current checklist of new reference books, and is designed to supplement the…
Abstract
The following classified, annotated list of titles is intended to provide reference librarians with a current checklist of new reference books, and is designed to supplement the RSR review column, “Recent Reference Books,” by Frances Neel Cheney. “Reference Books in Print” includes all additional books received prior to the inclusion deadline established for this issue. Appearance in this column does not preclude a later review in RSR. Publishers are urged to send a copy of all new reference books directly to RSR as soon as published, for immediate listing in “Reference Books in Print.” Reference books with imprints older than two years will not be included (with the exception of current reprints or older books newly acquired for distribution by another publisher). The column shall also occasionally include library science or other library related publications of other than a reference character.
Runqiang Zhang, Guoyong Sun, Yuchuan Wang and Sebastián Leguizamón
The study aims to display the bubbles' evolution in the shear layer and their relationship with the pressure fluctuations. Furthermore, the coherent structures of the first six…
Abstract
Purpose
The study aims to display the bubbles' evolution in the shear layer and their relationship with the pressure fluctuations. Furthermore, the coherent structures of the first six modes are extracted, in order to provide insight into their temporal and spatial evolution and determine the relationship between cavitating bubbles and coherent structures.
Design/methodology/approach
In the present study, numerical simulations of submerged jet cavitating flow were carried out at a cavitation inception condition inside an axisymmetric cavity using the large eddy simulation (LES) turbulence model and the Schnerr–Sauer (S–S) cavitation model. Based on snapshots produced by the numerical simulation, dynamic mode decomposition (DMD) was performed to extract the three-dimensional coherent structures of the first six modes in the shear layer.
Findings
The cavitating bubbles in the shear layer are deformed to elongated ellipsoid shapes by shear forces. The significant pressure fluctuations are induced by the collapse of the biggest bubble in the group. The first mode illustrates the mean characteristics of the flow field. The flow in the peripheral region of the shear layer is mainly dominated by large-scale coherent structures revealed by the second and third modes, while different small-scale coherent structures are contained in the central region. The cavitating bubbles are associated with small size coherent structures as the sixth or higher modes.
Practical implications
This work demonstrates the feasibility of LES for high Reynolds number shear layer flow. The dynamic mode decomposition method is a novel method to extract coherent structures and obtain their dynamic information that will help us to optimize and control the flow.
Originality/value
(1) This paper first displays the three-dimensional coherent structures and their characteristics in the shear layer of confined jet flow. (2) The relationship of bubbles shape and pressure fluctuations is illustrated. (3) The visualization of coherent structures benefits the understanding of the mixing process and cavitation inception in jet shear layers.
Details