A framework for the design by optimization of hydrofoils under cavitating conditions

Hydrodynamic shape optimization based on CFD calculations can dramatically improve the design of marine devices (i.e. propellers, rudders and appendages) by simultaneously considering opposite objectives and by modeling phenomena that well-established and still widely adopted design approaches (i.e. lifting line and lifting surface) cannot accurately deal with. Cavitation on propellers, for instance and among the others, is one of the most dangerous phenomena. It causes vibration, erosion and it is a source of radiated noise, consequently resulting incompatible with modern propeller design, continuously aimed for higher efficiency, comfort and environmentally safe operations. An accurate selection, firstly, of the most appropriate blade sections is, consequently, of crucial importance at least to limit the side effects of cavitation. In the present work, therefore, a numerical framework for the design by optimization of marine hydrofoils under cavitating conditions is proposed. By combining a parametric description of the hydrofoil shape, the NSGA-II multi-objective genetic algorithm and appropriate flow solvers, new hydrofoil shapes are derived. Objectives of the design are blade sections with enlarged cavitation buckets to increase the cavitation inception speed and to reduce the cavity volume (under the constraint of unchanged delivered lift) with respect to widely accepted NACA66 profiles. Boundary element methods and RANSE solvers (a proprietary Hess & Smith implementation and the open-source RANSE solver OpenFOAM) are applied in succession in order to verify the influence of the inviscid/viscous nature of the flow on the final optimal hydrofoil shape and of the additional maximum lift/drag ratio objective required in the case of viscous calculations

Aeronautical Engineering: A special bibliography with indexes, supplement 62

This bibliography lists 306 reports, articles, and other documents introduced into the NASA scientific and technical information system in September 1975

The Fifth Symposium on Numerical and Physical Aspects of Aerodynamic Flows

This volume contains the papers presented at the Fifth Symposium on Numerical and Physical Aspects of Aerodynamic Flows, held at the California State University, Long Beach, from 13 to 15 January 1992. The symposium, like its immediate predecessors, considers the calculation of flows of relevance to aircraft, ships, and missiles with emphasis on the solution of two-dimensional unsteady and three-dimensional equations

Hydrodynamic behaviour of gliding hydrofoil crafts

A new type of high-speed craft, called a Gliding-Hydrofoil Craft (GHC), has recently been developed in Jiangsu University of Science and Technology, China. This craft is similar to a planing hull but with a hydrofoil in the front part of its body. The fixed hydrofoil improves the seakeeping properties and stability of the craft compared with a conventional planing hull. In addition, the GHC has a more simple structure and higher stability when compared to a hydrofoil craft. Unlike conventional planing hulls and hydrofoil crafts, the study of hydrodynamics of GHC has been overlooked. The present work aims to advance our understanding on hydrodynamics of GHC, both model tests and numerical investigations are presented. To study its hydrodynamic characteristics, model tests are carried out in a towing tank, and the total resistance, trim angle and wetted area of the craft in the cases with different Froude numbers are measured. For the purpose of comparison, model tests have also been carried out for the hull without the hydrofoil. This thesis presents analysis on the experimental data and discusses the effects of the submerged depth and initial attack angle of the hydrofoil on the hydrodynamic features of the GHC. On this basis, the FLUENT software is then adopted to numerically investigate the hydrodynamics of the GHC. The accuracy of the FLUENT addressing this problem is validated by comparing the numerical solutions with the experimental data. The validation cases include 2D hydrofoil in current, Wigley hull with steady forward speed. Good agreement between numerical results and experimental data was obtained. Considering the significance of the turbulence involved in the problem, especially near the hydrofoil, a numerical investigation aiming to find a suitable turbulence model has been carried out. After being validated, 3D numerical simulations on both the planing craft and the GHC in steady flow are considered. The resistance coefficient, pressure coefficient and wave pattern with different Froude number are investigated. Some results are compared with experiment data obtained in the model tests. The wave pattern, velocity field and pressure distribution near the hulls are discussed in detail as well as the influence of the hydrofoil. Finally, the hydrodynamic performance of GHC in unsteady flow is investigated. Three cases were considered: ship berthing, leaving the harbour and turning navigation direction; which are very commonly seen unsteady examples in reality. The preliminary results presented in this thesis have confirmed the significant effects due to the unsteady procedure and imply the need of carrying out unsteady simulations in the future

Under-water noise pollution sources, mitigation measures in commercial vessels: the trade-off analysis in the case of study for trans mountain project, Port of Vancouver, Canada.

Shipping is the most efficient type of transportation and plays a significant role in global trade. However, it has some negative externalities and creates environmental pollution. With the growth of shipping, the potential for low-frequency noise increases along with its negative effects such as impacts on marine species and threat to sustainable shipping, e.g. its intensity has been doubling in the North Pacific Ocean every decade for the past 60 years and it is predicted to increase by 87–102% on average by 2030. In contrast to other environmental issues, the underwater noise is not visible, so to raise awareness and show its negative impacts, a scientific approach and data collection are required. While awareness of the society in respect of the other pollutions such as oil, dangerous goods, noxious liquids substances, sewage, and air has been raised and those issues are regulated properly, society has not been familiar with under-water noise pollution and it has not been regulated properly. As such, legal gaps exist this study is a holistic approach to UWN pollution. The main sources and the ways to mitigate UWN pollution and its effect on sustainable shipping will be reviewed. Meanwhile, with reference to the previous environmental issues and present information and data collection, the general trends for the future of UWN pollution will be suggested. Moreover, in the case study (the Trans Mountain Project (TMP)), mitigation measures to reduce the negative impacts of the growth of shipping in the Haro Strait will be suggested. Furthermore, by creating four scenarios and modelling, simulations, utilizing the MCDM (MADM) algorithms, and TOPSIS techniques the trade-off between the environmental (noise and Co2 emission) and economical (fuel cost) aspects of the project will be conducted to enhance the Decision Support System (DSS). This will help the decision makers to have a multi-dimensional thinking instead of the single dimensional thinking in addressing and tackling the negative externalities of the TMP in the area. Moreover, at the end of each scenario, a sensitivity analysis will be conducted to provide a clean environment for decision makers

Research in Natural Laminar Flow and Laminar-Flow Control, part 2

Part 2 of the Symposium proceedings includes papers addressing various topics in basic wind tunnel research/techniques and computational transitional research. Specific topics include: advanced measurement techniques; laminar flow control; Tollmien-Schlichting wave characteristics; boundary layer transition; flow visualization; wind tunnel tests; flight tests; boundary layer equations; swept wings; and skin friction

Numerical modelling of fluid-induced noise from lifting surfaces at moderate Reynolds numbers

Fluid-induced noise from lifting surface flows occurs in a wide variety of industrial applications and, despite decades of research, there are still many open questions relating to the underlying physics of how different flows produce particular acoustic signatures. Predicting fluid-induced noise is challenging and requires a detailed understanding of the underlying fluid flow. At moderate Reynolds numbers, the transitional nature of the flow makes the acoustic field very sensitive to small changes in the flow conditions, making predictions particularly difficult. This thesis presents a numerical study of fluid-induced noise over lifting surfaces. A hybrid aero-acoustic model is developed that is capable of resolving the acoustic field resulting from the turbulent flow over an arbitrary body or bodies. The methodology leads to a flexible and robust model that allows for both the fluid and acoustic fields to be resolved simultaneously on separate, partially overlapping domains, allowing for the separation of turbulent and acoustic scales to be handled in an efficient manner. The model is used, together with large eddy and direct numerical simulations, to investigate the fluid dynamics and fluid-induced noise of flows over lifting surfaces at moderate Reynolds numbers (o 10^5). The acoustics of finite and infinite span lifting surfaces are investigated, with a particular focus on trailing edge noise and its relationship to a transitional boundary layer. Multi-body interaction noise is also considered, with results comparing favourably with experimental data, providing a high degree of confidence in the predictive capabilities of the model

Performance prediction of cavitating propulsors using a viscous/inviscid method

textA viscous/inviscid interaction method for predicting the effect of viscosity on the performance of wetted and cavitating propulsors is presented. The emphasis is placed on steady wetted and cavitating propulsor flows. A three-dimensional low order potential based boundary element method is strongly coupled with a two dimensional integral boundary layer analysis method based on the strip theory assumption. The influence of viscosity on the outer inviscid flow is modeled through the wall transpiration model by distributing “blowing” sources on the propulsor blade and trailing wake surfaces. The boundary layer edge velocities are expressed as the sum of the inviscid edge velocity and a correction which depends only on the boundary layer variables. The influence of outer potential flow on the inner boundary layer flow is considered through the edge velocities. In the case of sheet cavitation, a “thin” cavity approach is employed and the viscous/inviscid interaction method is applied on the blade surface underneath the cavity. On the cavity surface, the friction force coefficient is forced to be zero. Numerical predictions by the present viscous/inviscid interaction method are presented for open, ducted, and water-jet propulsors. For water-jet propulsors, the flow is solved in an iterative manner by solving the rotor and stator problems separately and by considering the time-averaged effects of one component on the other. Predicted forces, pressure distributions, and boundary layer variables are compared with those predicted by other numerical methods and experimental measurements.Civil, Architectural, and Environmental Engineerin