scholarly journals A RANS-BEM Method to Efficiently Include Appendage Effects in RANS-Based Hull Shape Evaluation

2021 ◽  
Vol 6 (01) ◽  
pp. 44-57
Author(s):  
Hannes Renzsch ◽  
Britton Ward
Keyword(s):  
Pressure Distribution ◽  
Cell Count ◽  
Potential Flow ◽  
Initial Assessment ◽  
Time Requirement ◽  
Cpu Time ◽  
Momentum Theory ◽  
Pressure Fields ◽  
Time Requirements ◽  
Mass Sources

Abstract. In this paper an approach to mimic the influence of appendages on the pressure distribution on a boat’s hull in RANS simulations is given. While, of course, the appendages could be modelled explicitly in the RANS simulation, this significantly increases the cell count and CPU-time requirements of the simulations, particularly for boats with multiple appendages. In this approach it is assumed that the pressure fields generated by the appendages can be decomposed into two parts: one related to lift (asymmetric) and one related to the displaced volume (symmetric). For these parts actuator line momentum theory is utilized, and doublet mass sources are described based on potential flow theory. An initial assessment of the approach’s capabilities and accuracy is presented based on the SYRF wide light series (Claughton, 2015), showing good promise. An application example with particular focus on the reduction of CPU-time requirement is given based on a boat fitted with canting keel and DSS foil.

On the choice of CFD codes in the design process of planing sailing yachts

2009 ◽  
Author(s):  
Jérémie Raymond ◽  
Jean-Marie Finot ◽  
Jean-Michel Kobus ◽  
Gérard Delhommeau ◽  
Patrick Queutey ◽  
...  
Keyword(s):  
Free Surface ◽  
Design Process ◽  
Finite Differences ◽  
Potential Flow ◽  
Surface Condition ◽  
Cpu Time ◽  
Free Surface Condition ◽  
Finite Differences Method ◽  
Non Linear ◽  
Ranse Solver

The discussion is based on results gathered during the first two years of a 3 years research program for the benefits of Groupe Finot-Conq, Naval Architects. The introduction presents the objectives of the program: Setting up a practical method using numerical and experimental available tools to design fast planing sailing yachts. The aim of this paper is to compare advantages and disadvantages of four different kinds of CFD codes which are linear and non-linear potential flow approach, RANSE solver using finite differences method and RANSE solver using volume of fluid method. The Fluid Mechanics Laboratory of the Ecole Centrale de Nantes (France) has developed those three approaches so those homemade codes will be used for this study. The first one is REVA, a potential flow code with a linearised free surface condition. ICARE is a RANSE solver using finite differences method with a non linear free surface condition. It is extensively used for industrial projects as for sailing yachts projects (ACC for example). ISIS-CFD is a RANSE solver using finite volume method to build the spatial discretization of the transport equations with unstructured mesh. The latter is able to compute sprays for fast planing ships but is also the slower in terms of CPU time. In addition, we had the opportunity to test FS-FLOW which is a potential flow code with a non linear free surface condition distributed by FRIENDSHIP CONSULTING. Numerical results for the four codes are compared with the other codes' results as with tank tests data. Those tank tests were made using captive model test technique on two Open60' models. Reasons of the choice of the captive model technique are explained and experimental procedures are briefly described. Comparisons between codes are mainly based on the easiness of use, the cost in CPU time and the confidence we can have in the results as a function of the boat speed. Flow visualizations, pressure maps, free surface deformation are shown and compared. Analysis of local quantities integrated or by zone is also presented. Results are analyzed focusing on the ability of each code to represent flow dynamics for every speed with a special attention to high speeds. The practical question raised is to know which kind of answers each code can bring in terms of tendencies evaluation or sensitivity to hull geometry modifications. The main goal is to be able to judge if those codes are able to make reliable and consistent comparisons of different designs. Conclusion is that none of the codes is perfect and gather all the advantages. It is still difficult to propose a definitive methodology to estimate hydrodynamic performances at every speed and at every stage of the design process. Knowing each code limitations, it appears more coherent to use each of them at different stages of the design process: the quickest and less reliable to understand the main tendencies and the longest and more precise to validate the final options.

scholarly journals Aerodynamic analysis of multirotor vehicles using a higher-order potential flow method

2021 ◽  
Author(s):  
Devin F. Barcelos
Keyword(s):  
Performance Prediction ◽  
Potential Flow ◽  
Higher Order ◽  
Theory Approach ◽  
Blade Element Momentum Theory ◽  
Flow Method ◽  
Momentum Theory ◽  
Radial Loading ◽  
Rotational Direction ◽  
Blade Element

A higher-order potential flow method is adapted for the aerodynamic performance prediction of small rotors used in multirotor unmanned aerial vehicles. The method uses elements of distributed vorticity which results in numerical robustness with both a prescribed and relaxed wake representation. The radial loading and wake shapes of a rotor in hover were compared to experiment to show strong agreement for three disk loadings. The advancing flight performance prediction of a single rotor was compared to a single rotor was compared to a blade element momentum theory based approach and to experiment. Comparison showed good thrust and power agreement with experiment across a range of advance ratios and angles of attack. Prediction in descending flights showed improvements in comparison to the blade element momentum theory approach. The model was extended to a quadrotorm configuration showing the differences associated to vehicle orientation and rotor rotational direction.

Inverse or Design Calculations for Non-Potential Flow in Turbomachinery Blade Passages

1981 ◽  
Author(s):  
W. T. Thompkins ◽  
Siu Shing Tong
Keyword(s):  
Pressure Distribution ◽  
Potential Flow ◽  
Three Dimensional ◽  
Viscous Flows ◽  
Geometric Constraints ◽  
Design Calculation ◽  
Compressor Cascade ◽  
Surface Pressure Distribution ◽  
Blade Row ◽  
Design Calculations

A new inverse or design calculation procedure has been devised for non-potential flow fields and has been applied to turbomachinery blade row design. This technique uses as input quantities the surface pressure distribution and geometric constraints and may be used for two- or three-dimensional flows as well as inviscid or viscous flows. If a geometry satisfying both the constraints and the pressure distribution cannot be found, a solution satisfying the constraints and a relaxed pressure distribution is found. Calculational examples are presented for inviscid supersonic compressor cascade designs and the extension to three-dimensional flows discussed.

Methodology to Evaluate Slamming Loads on Ocean Platforms

2008 ◽  
Author(s):  
Marcio Domingues Maia Junior ◽  
Antonio Carlos Fernandes ◽  
Marcela Trindade ◽  
Andre Ramiro
Keyword(s):  
Free Surface ◽  
Pressure Distribution ◽  
Pressure Sensor ◽  
Potential Flow ◽  
Experimental Methods ◽  
The Body ◽  
Platform Motion ◽  
Air Pocket ◽  
Accuracy And Precision ◽  
The Impact

The purpose of the study is suggest a methodology to be applied in ocean platforms and ships in order to appraise the maximum impact pressure due to the slamming occurrence in the hull shape near its bottom or horizontal regions. This methodology uses a theory based on potential flow. However, there are some phenomena such as creation of a compressible air pocket between the body and free surface at the impact moment that requires a more complete theory and or experimental methods. This gives rise to experimental coefficients to reduce the theoretical errors. The procedure presented here goes by the platform motion dynamics and “impact topology” to allow the potential to be used. Due to the complexity of the phenomenon studied and need for certifying accuracy and precision of the results, tank tests at the LabOceano model basin were carried out. The results showed a good fitting between numerical results and experiments. It should also be pointed out that the pressure sensor used in these experiments gives a pressure distribution over the instrumented area what brings more reliability on the results and a better visibility to the slamming phenomenon. Lastly the methodology in this work stands out as an important tool to evaluate slamming loads.

The three-dimensional interaction of a streamwise vortex with a large-chord lifting surface: theory and experiment

1996 ◽  
Vol 322 ◽  
pp. 51-79 ◽  
Author(s):  
Gustavo C. R. Bodstein ◽  
Albert R. George ◽  
C.-Y. Hui
Keyword(s):  
Boundary Layer ◽  
Pressure Distribution ◽  
Potential Flow ◽  
Velocity Potential ◽  
Lateral Displacement ◽  
Three Dimensional ◽  
Leading Edge ◽  
Vortex Filament ◽  
Soap Bubble ◽  
Lifting Surface

The three-dimensional vortex flow that develops around a close-coupled canard-wing configuration is characterized by a strong interaction between the vortex generated at the canard and the aircraft wing. In this paper, a theoretical potential flow model is devised to uncover the basic structure of the pressure and velocity distributions on the wing surface. The wing is modelled as a semi-infinite lifting-surface set at zero angle of attack. It is assumed that the vortex is a straight vortex filament, with constant strength, and lying in the freestream direction. The vortex filament is considered to be orthogonal to the leading-edge, passing a certain height over the surface. An incompressible and steady potential flow formulation is created based on the three-dimensional Laplace's equation for the velocity potential. The boundary-value problem is solved analytically using Fourier transforms and the Wiener-Hopf technique. A closed-form solution for the velocity potential is determined, from which the velocity and pressure distributions on the surface and a vortex path correction are obtained. The model predicts an anti-symmetric pressure distribution along the span in region near the leading-edge, and a symmetric pressure distribution downstream from it. The theory also predicts no vertical displacement of the vortex, but a significant lateral displacement. A set of experiments is carried out to study the main features of the flow and to test the theoretical model above. The experimental results include helium-soap bubble and oil-surface flow pattern visualization, as well as pressure measurements. The comparison shows good agreement only for a weak interaction case, whereas for the case where the interaction is strong, secondary boundary-layer separation and vortex breakdown are observed to occur, mainly owing to the strong vortex-boundary layer interaction. In such a case the model does not agree well with the experiments.

scholarly journals Concussion Recovery Phase Affects Vestibular and Oculomotor Symptom Provocation

2017 ◽  
Vol 39 (02) ◽  
pp. 141-147 ◽  
Author(s):  
Kelly Cheever ◽  
Jane McDevitt ◽  
Ryan Tierney ◽  
W. Wright
Keyword(s):  
Recovery Process ◽  
Recovery Phase ◽  
Return To Play ◽  
Initial Assessment ◽  
Valuable Insight ◽  
Gaze Stabilization ◽  
Symptom Provocation ◽  
Acute Group ◽  
Time Requirements ◽  
Concussion Recovery

AbstractVestibular and oculomotor testing is emerging as a valuable assessment in sport-related concussion (SRC). However, their usefulness for tracking recovery and guiding return-to-play decisions remains unclear. Therefore the purpose of this study was to evaluate their clinical usefulness for tracking SRC recovery. Vestibular and oculomotor assessments were used to measure symptom provocation in an acute group (n=21) concussed≤10 days, prolonged symptoms group (n=10) concussed ≥16 days (median=84 days), healthy group (n=58) no concussions in >6 months. Known-groups approach was used with three groups at three time points (initial, 2-week and 6-week follow-up). Provoked symptoms for Gaze-Stabilization (GST), Rapid Eye Horizontal (REH), Optokinetic Stimulation (OKS), Smooth-Pursuit Slow (SPS) and Fast (SPF) tests, total combined symptoms scores and near point convergence (NPC) distance were significantly greater at initial assessment in both injury groups compared to controls. Injury groups improved on the King-Devick test and combined symptom provocation scores across time. The acute group improved over time on REH and SPF tests, while the prolonged symptoms group improved on OKS. A regression model (REH, OKS, GST) was 90% accurate discriminating concussed from healthy. Vestibular and ocular motor tests give valuable insight during recovery. They can prove beneficial in concussion evaluation given the modest equipment, training and time requirements. The current study demonstrates that when combined, vestibular and oculomotor clinical tests aid in the detection of deficits following a SRC. Additionally, tests such as NPC, GST, REH, SPS, SPF OKS and KD provide valuable information to clinicians throughout the recovery process and may aid in return to play decisions.

Transonic flow around the leading edge of a thin airfoil with a parabolic nose

1993 ◽  
Vol 248 ◽  
pp. 1-26 ◽  
Author(s):  
Z. Rusak
Keyword(s):  
Pressure Distribution ◽  
Stagnation Point ◽  
Asymptotic Expansions ◽  
Potential Flow ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Two Dimensional ◽  
Small Disturbance ◽  
Outer Expansion ◽  
Inner Region

Transonic potential flow around the leading edge of a thin two-dimensional general airfoil with a parabolic nose is analysed. Asymptotic expansions of the velocity potential function are constructed at a fixed transonic similarity parameter (K) in terms of the thickness ratio of the airfoil in an outer region around the airfoil and in an inner region near the nose. These expansions are matched asymptotically. The outer expansion consists of the transonic small-disturbance theory and it second-order problem, where the leading-edge singularity appears. The inner expansion accounts for the flow around the nose, where a stagnation point exists. Analytical expressions are given for the first terms of the inner and outer asymptotic expansions. A boundary value problem is formulated in the inner region for the solution of a uniform sonic flow about an infinite two-dimensional parabola at zero angle of attack, with a symmetric far-field approximation, and with no circulation around it. The numerical solution of the flow in the inner region results in the symmetric pressure distribution on the parabolic nose. Using the outer small-disturbance solution and the nose solution a uniformly valid pressure distribution on the entire airfoil surface can be derived. In the leading terms, the flow around the nose is symmetric and the stagnation point is located at the leading edge for every transonic Mach number of the oncoming flow and shape and small angle of attack of the airfoil. The pressure distribution on the upper and lower surfaces of the airfoil is symmetric near the edge point, and asymmetric deviations increase and become significant only when the distance from the leading edge of the airfoil increases beyond the inner region. Good agreement is found in the leading-edge region between the present solution and numerical solutions of the full potential-flow equations and the Euler equations.

scholarly journals Position accuracy and repeatability calibration of turn tables by using laser interferometers

2019 ◽  
Author(s):  
İ. Ahmet Yüksel ◽  
T. Oytun Kılınç ◽  
K. Berk Sönmez ◽  
Sinem Ön Aktan
Keyword(s):  
Laser Interferometer ◽  
Horizontal Axis ◽  
Time Requirement ◽  
Rotary Axis ◽  
Position Accuracy ◽  
Alternative Method ◽  
Time Requirements ◽  
Accuracy And Repeatability ◽  
Laser Interferometers

This paper presents how to perform position accuracy calibration of multi axis turntable with a laser interferometer according to ISO-230-2 Determination of accuracy and repeatability of positioning of numerically controlled axes standard [1]. High accurate multi-axis turn tables are frequently used at defense and aviation & space industries. These turn tables are used to control of devices which collect data regarding position. So turn tables shall be calibrated periodically to remain between specification performances criteria. Calibration of a rotary axis of turn tables’ position is commonly performed by using autocollimator and multi-sided polygon systems. Alignment of polygon and autocollimator with turn table axes may have difficulties regarding time requirements and setup of hardware. Laser interferometers can be used as an alternative method to regular calibration of position and repeatability of an axis with advantages considering time requirement and ease of application. In this study, position accuracy and repeatability calibration of a horizontal axis which has ± 3 arc second will be performed and results will be evaluated.

Study of Power Augmented Ram Vehicles

2009 ◽  
Author(s):  
K. I. Matveev
Keyword(s):  
Pressure Distribution ◽  
Potential Flow ◽  
Water Surface ◽  
Surface Deformation ◽  
Ground Effect ◽  
Forward Speed ◽  
Friction Forces ◽  
Air Jets ◽  
Platform System ◽  
Scaled Models

Power Augmented Ram Vehicle is an innovative type of air-assisted fast amphibious transport platform. This craft operates in ground effect and employs propulsor jets for partial or complete support of the vehicle weight. The present paper reviews recent experiments and modeling studies aimed at aero-hydrodynamics phenomena. Representative results of our previous work with static platforms are shown here for (i) recovered thrust and lift of scaled models on both solid and water surfaces, (ii) potential flow theory for air jets with inclusion of effects of the water surface deformation and friction forces, and (iii) pressure distribution under a platform. New results in this paper are presented for (i) front flap augmentation of platform lift, (ii) speed tests of a radio-controlled model on various surfaces, and (iii) viscous simulations of forward-speed motion of a propulsor-platform system. Overall, a progress has been made toward better understanding of aero-hydrodynamics of jet-augmented fast amphibious platforms.

The force on a sphere moving through a conducting fluid in the presence of a magnetic field

1961 ◽  
Vol 11 (1) ◽  
pp. 133-142 ◽  
Author(s):  
J. R. Reitz ◽  
L. L. Foldy
Keyword(s):  
Magnetic Field ◽  
Reynolds Number ◽  
Pressure Distribution ◽  
Magnetic Field Line ◽  
Potential Flow ◽  
Uniform Magnetic Field ◽  
Magnetic Reynolds Number ◽  
Conducting Fluid ◽  
Joule Dissipation ◽  
Hydrodynamic Motion

The force on a sphere moving through an inviscid, conducting fluid in the presence of a uniform magnetic field B0 is calculated for the low-conductivity case where the hydrodynamic motion deviates only slightly from potential flow. The magnetic Reynolds number is assumed small. The force on the sphere is found to consist of both a drag and a deflective component which tends to orient its motion parallel to a magnetic field line; if the sphere's velocity is V, the force may be written $\bf {R} = -AB^2_0\bf {V} + \bf C(V.B_0)B_0$ where the coefficients A and C depend on the conductivities of both sphere and fluid. The coefficients are evaluated by calculating the Joule dissipation for particular orientations of V relative to B0. In one case the force is also calculated directly from the perturbed pressure distribution in the fluid. In an analogous way, a spinning sphere in a conducting fluid experiences both resistive and gyroscopic torques.

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