STATIC CONTROL OF DRAG-REDUCING AIR CAVITIES WITH VARIABLE CAVITATOR SHAPE

2021 ◽  
Vol 161 (A1) ◽  
Author(s):  
K I Matveev
Keyword(s):  
Drag Reduction ◽  
High Performance ◽  
Wedge Angle ◽  
Flow Speed ◽  
Frictional Drag ◽  
Air Cavity ◽  
Operational Conditions ◽  
Ship Hulls ◽  
Air Ventilation ◽  
Air Cavities

Air ventilation of submerged surfaces of ship hulls is a promising technique for drag reduction. To ensure high performance of air cavities in a broad range of operational conditions, the cavity properties can be controlled with help of compact hydrodynamic actuators. In this study, a potential flow theory is applied to model an air cavity formed behind a wedge-shaped cavitator under a horizontal wall imitating a ship bottom. By varying the wedge angle, it is possible to achieve states with maximum drag reduction at given operational conditions. The dependence of the optimal wedge angle on Froude number and hull trim is investigated. The air-cavity ability to reduce frictional drag is found to increase with rising flow speed and bow-down hull trim.

Static Control of Drag-Reducing Air Cavities with Variable Cavitator Shape

2019 ◽  
Vol 161 (A1) ◽  
Keyword(s):  
Drag Reduction ◽  
High Performance ◽  
Wedge Angle ◽  
Flow Speed ◽  
Frictional Drag ◽  
Air Cavity ◽  
Operational Conditions ◽  
Ship Hulls ◽  
Air Ventilation ◽  
Air Cavities

Air ventilation of submerged surfaces of ship hulls is a promising technique for drag reduction. To ensure high performance of air cavities in a broad range of operational conditions, the cavity properties can be controlled with help of compact hydrodynamic actuators. In this study, a potential flow theory is applied to model an air cavity formed behind a wedge-shaped cavitator under a horizontal wall imitating a ship bottom. By varying the wedge angle, it is possible to achieve states with maximum drag reduction at given operational conditions. The dependence of the optimal wedge angle on Froude number and hull trim is investigated. The air-cavity ability to reduce frictional drag is found to increase with rising flow speed and bow-down hull trim.

Control of Air-Ventilated Cavity Under Ship Hull in Abnormal Waves

2019 ◽  
Author(s):  
Konstantin I. Matveev
Keyword(s):  
High Amplitude ◽  
Maritime Transportation ◽  
Practical Implementation ◽  
Frictional Drag ◽  
Air Cavity ◽  
Fuel Savings ◽  
Ship Hulls ◽  
Reduction Techniques ◽  
Air Supply ◽  
Air Cavities

Abstract Practical implementation of ship drag reduction techniques can lead to substantial fuel savings and lessening environmental impacts of maritime transportation. One of such technologies is based on injecting air underneath ship hulls, which results in the formation of thin air cavities that decrease the wetted hull surface and hence its frictional drag. In realistic sea wave conditions, however, these cavities become unsteady and may easily disintegrate upon interaction with high-amplitude abnormal waves. In this study, the air-cavity dynamics in such situations is simulated with a potential flow model and empirical correlations. A method for controlling the air cavity by varying the air supply rate is numerically investigated. It is shown that degradation of the air-cavity power savings in the event of a rogue wave passing can be partly mitigated by briefly boosting the air supply right after the abnormal wave occurrence. For one considered example, it is found that 20% of power savings is lost in a condition with abnormal waves and constant air supply. In case of temporary augmentation of air injection, the overall decrease of power savings is reduced to 10%.

Study of the Suitability between Artificial Cavity and Traffic Vessel

2013 ◽  
Vol 401-403 ◽  
pp. 282-286
Author(s):  
Ji Sheng Li ◽  
Wen Cai Dong ◽  
Yong Peng Ou
Keyword(s):  
Drag Reduction ◽  
Cavity Flow ◽  
Multiphase Model ◽  
Flat Bottom ◽  
Air Cavity ◽  
Rans Equations ◽  
Ship Hulls ◽  
Artificial Cavity ◽  
Air Cavities

The use of air cavities beneath ship hulls can lead to significant drag reduction. A study of air-ventilated cavities under a traffic vessel with flat bottom has been undertaken based on solving the RANS equations and VOF multiphase model. Macroscopic features in the air-cavity flow are predicted. Why the existing cavity form leads to unsatisfactory results on the traffic vessel is analyzed. The influence of parameters of artificial cavity on air cavity patterns is parametrically studied. Suggestions on improving cavity parameters and a new cavity form that can obtain stable air cavity are given, which may provide reference for the design of air cavity traffic vessels.

Modification of Air Cavity Flow Under Model Hull With Hydrodynamic Actuators

2019 ◽  
Author(s):  
Matthew V. Pace ◽  
Konstantin I. Matveev
Keyword(s):  
Limited Range ◽  
Small Scale ◽  
Sea Waves ◽  
Frictional Drag ◽  
Air Cavity ◽  
Ship Hulls ◽  
Positive Effects ◽  
Wetted Area ◽  
External Water ◽  
Air Cavities

Abstract Air cavities employed under ship hulls can result in significant decrease of the water frictional drag by reducing the hull wetted area. However, these cavities usually perform well only in a limited range of the ship speed and attitude. In off-design states and in the presence of sea waves, efficient air cavities covering large areas of the hull are difficult to form and maintain. This problem can be potentially addressed with help of hydrodynamic actuators, such as compact hydrofoils, tabs, and spoilers, which can assist with forming and maintaining air cavities under ship hulls. In this study, exploratory tests have been conducted with a simplistic small-scale hull having a bottom recess. Air was supplied into the recess to produce an air cavity, and several actuators were implemented and manually controlled during the tests. Subjected to external water flow, the air cavity under the hull was found to be responsive to variable positions of the actuators. Positive effects on the air cavity produced with specific actuator settings are identified and discussed in the paper. A series of experimental photographs of the air-water interface are shown for various actuator settings. The air flow rates needed to establish and maintain a large air cavity under the model hull are also reported.

scholarly journals Simplified model for unsteady air cavities under ship hulls

2019 ◽  
Vol 234 (1) ◽  
pp. 100-107
Author(s):  
Konstantin I Matveev
Keyword(s):  
System Optimization ◽  
Practical Implementation ◽  
Air Cavity ◽  
Ship Hulls ◽  
Air Supply ◽  
Cavity System ◽  
Air Pockets ◽  
Air Cavities ◽  
Solid Walls ◽  
Unsteady Conditions

The drag reduction technique involving air cavities under ship hulls is a promising energy-saving technology. Understanding the air cavity dynamics in unsteady conditions and developing methods for the air cavity system optimization are critically important for practical implementation of this technology. In this study, a potential-flow theory is applied for modeling the air cavities under solid walls in water flow with fluctuating pressure. The present modeling approach incorporates detachment of macroscopic air pockets from the cavity tail. For specific configurations considered in this article, it is found that a change of the rate of air supply into the cavity can partly mitigate degradation of the overall power savings by the air cavity system in unsteady conditions.

scholarly journals Numerical Investigation of High-Reynolds-Number Air-Ventilated Water Flow under Solid Body with Surface Geometry Variations

Fluids ◽  
2021 ◽  
Vol 6 (5) ◽  
pp. 174
Author(s):  
Konstantin I. Matveev ◽  
Jeffrey M. Collins
Keyword(s):  
Stability Boundary ◽  
Practical Interest ◽  
The Body ◽  
Surface Geometry ◽  
Air Cavity ◽  
Operational Conditions ◽  
Marine Vehicles ◽  
Air Supply ◽  
High Reynolds ◽  
Air Cavities

Air-ventilated cavities formed under or around the hulls of marine vehicles can reduce water drag. Hull configurations with partial air ventilation where air cavities reattach to body surfaces are of special practical interest, since the required air supply rates to achieve significant drag reduction can be made rather low. However, formation and stability of such air cavities are sensitive to the hull geometry and operational conditions. In this study, an attempt is made to numerically simulate one setup with a partial air cavity that was previously tested experimentally at high Reynolds numbers, above 50 million. A computational fluid dynamics software Star-CCM+ has been employed for numerical modeling. Stable and unstable states of the air-cavity setup, characterized by long and collapsing air cavities, respectively, were modeled at two air supply rates near the stability boundary. Numerical results were similar to experimental data at the optimal water speed for the tested geometry, when a long air cavity was sustained at a minimal air supply rate. For water speeds that were substantially higher or lower than the optimal case, a stable cavity could not be maintained with small air supply rates for the given hull geometry. Numerical simulations demonstrated how alterations of the body surface could help sustain long air cavities across a broader speed range using air supply rates that were similar to the optimal case. These findings suggest that morphing hull surfaces can potentially be used for control of drag-reducing air cavities and expand the viable operating range for their application to marine vehicles.

scholarly journals Plunging Airfoil: Reynolds Number and Angle of Attack Effects

Aerospace ◽  
2021 ◽  
Vol 8 (8) ◽  
pp. 216
Author(s):  
Emanuel A. R. Camacho ◽  
Fernando M. S. P. Neves ◽  
André R. R. Silva ◽  
Jorge M. M. Barata
Keyword(s):  
Reynolds Number ◽  
High Performance ◽  
Angle Of Attack ◽  
Systems Design ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Low Reynolds Numbers ◽  
Operational Conditions ◽  
Naca0012 Airfoil ◽  
The Mean

Natural flight has consistently been the wellspring of many creative minds, yet recreating the propulsive systems of natural flyers is quite hard and challenging. Regarding propulsive systems design, biomimetics offers a wide variety of solutions that can be applied at low Reynolds numbers, achieving high performance and maneuverability systems. The main goal of the current work is to computationally investigate the thrust-power intricacies while operating at different Reynolds numbers, reduced frequencies, nondimensional amplitudes, and mean angles of attack of the oscillatory motion of a NACA0012 airfoil. Simulations are performed utilizing a RANS (Reynolds Averaged Navier-Stokes) approach for a Reynolds number between 8.5×103 and 3.4×104, reduced frequencies within 1 and 5, and Strouhal numbers from 0.1 to 0.4. The influence of the mean angle-of-attack is also studied in the range of 0∘ to 10∘. The outcomes show ideal operational conditions for the diverse Reynolds numbers, and results regarding thrust-power correlations and the influence of the mean angle-of-attack on the aerodynamic coefficients and the propulsive efficiency are widely explored.

The Sound the Air Makes: High-Performance Tunable Filters Based on Air-Cavity Resonators

2014 ◽  
Vol 15 (5) ◽  
pp. 83-93 ◽  
Author(s):  
Ming Yu ◽  
Bahram Yassini ◽  
Brian Keats ◽  
Ying Wang
Keyword(s):  
High Performance ◽  
Tunable Filters ◽  
Air Cavity ◽  
Cavity Resonators

Apparent and True Charges in the Partial Discharge Model at Different Defective Domain Sizes

2021 ◽  
Vol 64 (6) ◽  
pp. 94-100
Author(s):  
Nikolay Ignatev ◽  
◽  
Sergey Tetiora ◽  
Dmitry Turkin ◽  
◽  
...  
Keyword(s):  
Equivalent Circuit ◽  
Partial Discharge ◽  
Diagnostic Value ◽  
Partial Discharges ◽  
Active Resistance ◽  
Air Cavity ◽  
Discharge Ignition ◽  
Discharge Model ◽  
Air Cavities ◽  
Solid Insulation

A model of the partial discharges in a sample of solid insulation with air cavity is presented. The material of the insulation is cross-linked polyethylene. The model is based on an active-capacitive equivalent circuit, in which the resistance of the air cavity at the instant of a partial discharge ignition is shunted by the active resistance of the spark. The model takes into consideration the delay of the discharge development. The evaluation of the diagnostic value of the apparent and true charges is carried out. The results of the apparent and true charges relationship with the dimensions and proportions of the air cavity are presented. It is shown that the same magnitude of both true and apparent charges can correspond to the different volumes and shapes of the air cavities in the insulation.

Sign in / Sign up

Export Citation Format

Share Document