Accurate decomposition method and identification technology of drag

2020 ◽  
Vol 34 (14n16) ◽  
pp. 2040114
Author(s):  
Jia-Lei Yu ◽  
Jing Jin ◽  
Chun Shao ◽  
Miao Zhang ◽  
Tie-Jun Liu
Keyword(s):  
Shock Wave ◽  
Integral Method ◽  
Physical Mechanism ◽  
Wave Drag ◽  
Irreversible Processes ◽  
Viscous Drag ◽  
Numerical Dissipation ◽  
Far Field ◽  
Induced Drag ◽  
Field Integral

Aiming at accurate decomposition and identification of drag, the drag prediction technology based on the mid/far-field integral method is developed. The method decomposes the far-field drag into entropy drag and induced drag according to its physical mechanism, and introduces an appropriate entropy correction to eliminate the numerical dissipation by analyzing the influence of the trailing integral section position on the entropy drag calculation. Based on the analysis of thermodynamic reversible processes and irreversible processes, the drag is refined into viscous drag, shock wave drag, induced drag and pseudo-drag. The mid-field integral method is used to calculate the separate contribution of viscous drag, shock wave drag and induced drag by calculating the limited integral domain. Numerical results show that the developed method is feasible in accurately reflecting the physical mechanism and predicting the drag ratio. Thus, it provides a reliable tool for drag reduction of large passenger aircraft.

SPLASH Nonlinear and Unsteady Free-Surface Analysis Code for Grand Prix Yacht Design

1997 ◽  
Author(s):  
Bruce S. Rosen ◽  
Joseph P. Laiosa
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Inviscid Flow ◽  
Wave Drag ◽  
Surface Flow ◽  
Viscous Drag ◽  
Accurate Estimation ◽  
Following Seas ◽  
Induced Drag ◽  
Lifting Surfaces

The SPLASH free-surface potential flow panel code computer program is presented. The 3D flow theory and its numerical implementation are discussed. Some more conventional applications are reviewed, for steady flow past solid bodies, and for classical linearized free-surface flow. New free-surface capabilities are also described, notably, steady nonlinear solutions, and novel unsteady partially­nonlinear solutions in the frequency domain. The inviscid flow method treats both free-surface waves and lifting surfaces. The calculations yield predictions for complex interactions at heel and yaw such as wave drag due to lift, the effect of the free­surface on lift and lift-induced drag, and unsteady motions and forces in oblique or following seas. These are in addition to the usual predictions for the simpler effects considered separately, for example double-body lift and induced drag, and upright steady wave resistance or added resistance in head seas. For prediction of total resistance, the use of computed variable wetted areas and wetted lengths in a standard semi-empirical, handbook-type "viscous stripping" algorithm provides a more accurate estimation of viscous drag than is possible otherwise. Results from a variety of IACC and IMS yacht design studies, including comparisons with experimental data, support the conclusion that the free­surface panel code can be used for reliable and accurate prediction of sailboat performance.

scholarly journals Comparison of oblique shock wave angle in analytical and numerical solution

2019 ◽  
Vol 31 ◽  
pp. 137-142 ◽  
Author(s):  
Assen Marinov
Keyword(s):  
Shock Wave ◽  
Shock Waves ◽  
Wave Drag ◽  
Oblique Shock Wave ◽  
Friction Drag ◽  
Total Drag ◽  
Induced Drag ◽  
Drag And Lift ◽  
Wave Angle

The drag of the subsonic aircraft is largely formed by the skin friction drag and lift-induced drag. At transonic flight occurs shock wave. Determination of shock wave angle is important part of design of every aircraft, which working in supersonic airflow regimes. Formation of shock waves cause formation the wave drag. The wave drag could account about 35% from total drag of aircraft. Shock wave angle is directly linked with the intensity of itself. This work compares shock wave angle calculations using analytical and numerical solving methods.

Far-field drag decomposition using hybrid formulas and vorticity based area sensors

2020 ◽  
pp. 095441002097390
Author(s):  
L Qiao ◽  
XL He ◽  
Y Sun ◽  
JQ Bai ◽  
L Li
Keyword(s):  
Flow Field ◽  
Axial Velocity ◽  
Near Field ◽  
Three Dimensional ◽  
Field Method ◽  
Wave Drag ◽  
Viscous Drag ◽  
Far Field ◽  
Velocity Defect ◽  
Detection Failure

Numerical simulation of flow-field has become an indispensable tool for aerodynamic design. Usually, wall surface integration is a tool used to calculate values of pressure drag and skin friction drag, but the aerodynamic mechanism of drag production is still confusing. In present work, in order to decompose the total drag into viscous drag, wave drag, induced drag, and spurious drag, a far-field drag decomposition (FDD) method is developed. This method depends on axial velocity defect and area sensor functions. The present work proposes three hybrid formulas for velocity defect to tackle the negative square root issue by analyzing the existing axial velocity defect formulas. For dealing with the issue of detection failure for near-wall cells, a novel vorticity based viscous area sensor function is proposed. The new area sensor function is also independent of the turbulence model, which ensures easy application to general simulation methods for flow-field. Three tests cases are there to validate the proposed FDD method. The three dimensional transonic CRM test case shows that the present improvement is crucial for accurate drag decomposition. Excellent agreement between total decomposed drags and results from the near-field method or experimental data further confirms the correctness.

scholarly journals Can Radiators Be Really Isotropic?

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
H. Matzner ◽  
E. Levine
Keyword(s):  
Current Density ◽  
Integral Method ◽  
Function Analysis ◽  
Finite Size ◽  
Surface Current ◽  
Real Space ◽  
Far Field ◽  
Surface Current Density ◽  
Power Radiation ◽  
Field Integral

In search for isotropic radiators with reasonable quality Factor (Q), bandwidth, and efficiency, one looks for practical radiators with a typical resonant length of . We present here a Green's function analysis in Fourier of a microstrip element and a far-field integral method in configuration (real) space of single and dual U-shaped elements. Both solutions analytically prove that the power radiation patterns are isotropic in nature (while the thickness and the width tend to zero), although the polarizations are not symmetrical in all cuts. It is also shown that the power isotropic U-shaped radiator, for which the surface current density is infinite, can be replaced by another finite-size radiator, having finite-surface current density, such that its far-field is exactly the same as the far-field of the U-shaped isotropic radiator.

Acoustic invisibility in turbulent fluids by optimised cloaking

2014 ◽  
Vol 749 ◽  
pp. 460-477 ◽  
Author(s):  
Xun Huang ◽  
Siyang Zhong ◽  
Xin Liu
Keyword(s):  
Theoretical Model ◽  
Computational Methods ◽  
Physical Mechanism ◽  
Far Field ◽  
Turbulent Wakes ◽  
Scattered Fields ◽  
Turbulent Fluids

AbstractAcoustic invisibility of a cloaking system in turbulent fluids is poorly understood. Here we show that evident scattering would appear in turbulent wakes due to the submergence of a classical cloaking device. The inherent physical mechanism is explained using our theoretical model, which eventually inspires us to develop an optimised cloaking approach. Both the near- and far-field scattered fields are examined using computational methods. The remarkably low scattering demonstrates the effectiveness of the proposed approach, in particular for acoustic cloaking in turbulent fluids.

Application of Ship-Wave Theory to the Hydrofoil of Finite Span

1957 ◽  
Vol 1 (02) ◽  
pp. 27-55
Author(s):  
John P. Breslin
Keyword(s):  
Wave Theory ◽  
Wave Pattern ◽  
Wave Drag ◽  
Test Results ◽  
Dimensional Theory ◽  
Ship Hydrodynamics ◽  
Finite Span ◽  
Induced Drag ◽  
Load Distributions ◽  
The Waves

It is demonstrated in this paper2 that the deepwater wave drag of a hydrofoil of finite span can be found directly from the theory developed largely for ship hydrodynamics by Havelock and others. The wave drag is then studied at high Froude numbers and from the observed behavior the induced drag of the hydrofoil can be deduced from existing aerodynamic formulas. Evaluation of the resulting formulas is effected for two arbitrary load distributions and a comparison with some model test results is made. A practical approximation which gives the influence of gravity over a range of high Froude numbers is found and from this one can deduce a Froude number beyond which the effects of gravity may be ignored. It is also shown that an expression for the waves at some distance aft of the hydrofoil can be deduced from the general formulas developed for ship hydrodynamics. A discussion of the wave pattern is given with particular emphasis on the centerline profile at high Froude numbers and a contrast is pointed out in regard to the results of the two-dimensional theory for the hydrofoil waves and wave resistance.

Performance Prediction Hoftware for IACC Yachts

1993 ◽  
Author(s):  
Eric C. Schlageter ◽  
James R. Teeters
Keyword(s):  
Performance Prediction ◽  
Linear Optimization ◽  
Viscous Drag ◽  
Development Effort ◽  
Added Resistance ◽  
Induced Drag ◽  
Software Development Effort ◽  
Tank Test ◽  
America’S Cup ◽  
Wetted Area

The performance prediction software development effort undertaken by the Partnership for America's Cup Technology (PACT) is reviewed. First, PACT's origin, members, and mandate is covered, interspersed with a historical perspective of prediction software. Next, the new IACC rule with constraints is given. The hydrodynamic model format used in the software is described. Based on PACT tank test data, improved formulations for viscous drag, utilizing dynamic wetted area and length for canoe body drag and a 'stripping' method for appendage drag are presented. Corrections for Froude number and heel effects on induced drag are summarized. A new upwind sail model and added resistance model are discussed. The use of a race modeling program is illustrated with results from three separate design studies: a geosim family, a length scaling family, and an appendage study. Typical upright resistance, drag polar plots, lift plots, sea spectra, and added resistance data are presented. The final section describes current developments including speed enhancements, improved portability, and use of a multi-variable, non-linear optimization scheme to search the design space.

scholarly journals The collapse of single bubbles and approximation of the far-field acoustic emissions for cavitation induced by shock wave lithotripsy

2011 ◽  
Vol 677 ◽  
pp. 305-341 ◽  
Author(s):  
A. R. JAMALUDDIN ◽  
G. J. BALL ◽  
C. K. TURANGAN ◽  
T. G. LEIGHTON
Keyword(s):  
Shock Wave ◽  
Shock Wave Lithotripsy ◽  
Near Field ◽  
Acoustic Emissions ◽  
Clinical Situation ◽  
Control Surface ◽  
Bubble Collapse ◽  
Far Field ◽  
Field Emissions ◽  
Computational Resources

Recent clinical trials have shown the efficacy of a passive acoustic device used during shock wave lithotripsy (SWL) treatment. The device uses the far-field acoustic emissions resulting from the interaction of the therapeutic shock waves with the tissue and kidney stone to diagnose the effectiveness of each shock in contributing to stone fragmentation. This paper details simulations that supported the development of that device by extending computational fluid dynamics (CFD) simulations of the flow and near-field pressures associated with shock-induced bubble collapse to allow estimation of those far-field acoustic emissions. This is a required stage in the development of the device, because current computational resources are not sufficient to simulate the far-field emissions to ranges of O(10 cm) using CFD. Similarly, they are insufficient to cover the duration of the entire cavitation event, and here simulate only the first part of the interaction of the bubble with the lithotripter shock wave in order to demonstrate the methods by which the far-field acoustic emissions resulting from the interaction can be estimated. A free-Lagrange method (FLM) is used to simulate the collapse of initially stable air bubbles in water as a result of their interaction with a planar lithotripter shock. To estimate the far-field acoustic emissions from the interaction, this paper developed two numerical codes using the Kirchhoff and Ffowcs William–Hawkings (FW-H) formulations. When coupled to the FLM code, they can be used to estimate the far-field acoustic emissions of cavitation events. The limitation of the technique is that it assumes that no significant nonlinear acoustic propagation occurs outside the control surface. Methods are outlined for ameliorating this problem if, as here, computational resources cannot compute the flow field to sufficient distance, although for the clinical situation discussed, this limitation is tempered by the effect of tissue absorption, which here is incorporated through the standard derating procedure. This approach allowed identification of the sources of, and explanation of trends seen in, the characteristics of the far-field emissions observed in clinic, to an extent that was sufficient for the development of this clinical device.

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