scholarly journals Steady hydrodynamic interaction between human swimmers

2019 ◽  
Vol 16 (150) ◽  
pp. 20180768 ◽  
Author(s):  
Zhi-Ming Yuan ◽  
Mingxin Li ◽  
Chun-Yan Ji ◽  
Liang Li ◽  
Laibing Jia ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Hydrodynamic Interaction ◽  
Surface Effect ◽  
Swimming Performance ◽  
Interactive Effect ◽  
Free Water ◽  
Wave Drag ◽  
Competitive Swimming ◽  
Flow Solver ◽  
Wave Interference

This study focuses on the hydrodynamic interaction between two or three human swimmers in competitive swimming. Although the swimming performance of a single swimmer has been widely examined, studies on the interaction between multiple competitive swimmers are very rare. Experiments showed evidence that the drag of a swimmer could be modified by the existence of the other adjacent competitors (Chatard & Wilson. 2003 Med. Sci. Sports Exerc . 35 , 1176–1181. ( doi:10.1249/01.MSS.0000074564.06106.1F )). The following questions arise: (1) what mechanism determines the interaction; (2) which position experiences drag reduction or drag increase; (3) how much can drag be reduced or increased in a formation? According to the authors' knowledge, such questions have not been addressed by any published literature. Therefore, the main purpose of this study is to find the mechanism of the hydrodynamic interaction between human swimmers and to quantify this interactive effect by using a steady potential flow solver. The free-surface effect was fully taken into account in our calculations. We firstly calculated the wave drag of a swimmer swimming solely in an open swimming pool. Then we calculated the wave drag of the same swimmer when he/she swam in the wake region of one or two leading swimmers. The results showed that the hydrodynamic interaction made a significant contribution to the drafter's wave drag. By following a leading swimmer, a drafter at wave-riding positions could save up to 63% of their wave drag at speed of 2.0 m s −1 and lateral separation of 2.0 m. Particularly, when a drafter is following two side-by-side leaders, the drag reduction could even be doubled. To the authors' knowledge, this study is the first to demonstrate that the hydrodynamic interaction between human swimmers can best be described and explained in terms of wave interference effect on the free water surface. When the wave cancellation effect is observed, the wave drag of a drafter could be minimized, and this wave cancellation effect can be achieved only when the drafter is in a wave-riding position.

Investigation of Energy Deposition Technique for Drag Reduction at Hypersonic Speeds

2013 ◽  
Vol 367 ◽  
pp. 222-227 ◽  
Author(s):  
John Bibin ◽  
Kulkarni Vinayak
Keyword(s):  
Energy Source ◽  
Drag Reduction ◽  
Wave Drag ◽  
Aerodynamic Heating ◽  
Flow Solver ◽  
Reduction Techniques ◽  
Hypersonic Speeds ◽  
Parametric Studies ◽  
Energy Addition ◽  
Hypersonic Aerodynamics

Reduction in aerodynamic heating is the major design concern for hypersonic or hypervelocity vehicles which makes typical configurations blunt nosed for this flow regime. These blunt configurations make the space flight costlier due to higher wave drag. Therefore development and optimization of drag reduction techniques is the field of investigation and research in the area of hypersonic aerodynamics. The present work focuses on the investigation of concentrated energy addition technique for drag reduction. An in-house developed high precision compressible flow solver has been employed for the computational investigation of this technique. Parametric studies are carried out to investigate the effect of strength of energy source, location of energy addition and size of energy source.

DYNAMICS OF COUNTER-FLOW INJECTION FOR WAVE DRAG REDUCTION

2018 ◽  
Author(s):  
Vishnu Prakash K ◽  
Siddesh Desai ◽  
Hrishikesh Gadgil ◽  
Vinayak Kulkarni
Keyword(s):  
Drag Reduction ◽  
Flow Injection ◽  
Wave Drag ◽  
Counter Flow ◽  
Wave Drag Reduction

Blunt-body wave drag reduction using focused energy deposition

AIAA Journal ◽  
1999 ◽  
Vol 37 ◽  
pp. 460-467 ◽  
Author(s):  
David Riggins ◽  
H. F. Nelson ◽  
Eric Johnson
Keyword(s):  
Drag Reduction ◽  
Energy Deposition ◽  
Blunt Body ◽  
Body Wave ◽  
Wave Drag ◽  
Wave Drag Reduction

A numerical study on the single pulsed energy addition based unsteady wave drag reduction at varied hypersonic flow regimes

2020 ◽  
pp. 095441002097313
Author(s):  
Dathi SNV Rajasekhar Rao ◽  
Bibin John
Keyword(s):  
Steady State ◽  
Mach Number ◽  
Drag Reduction ◽  
Shock Layer ◽  
Blunt Body ◽  
Wave Drag ◽  
Flow Features ◽  
Energy Pulse ◽  
Energy Addition ◽  
Wave Drag Reduction

In this study, unsteady wave drag reduction in hypersonic flowfield using pulsed energy addition is numerically investigated. A single energy pulse is considered to analyze the time-averaged drag reduction/pulse. The blast wave creation, translation and its interaction with shock layer are studied. As the wave drag depends only on the inviscid aspects of the flowfield, Euler part of a well-established compressible flow Navier-Stokes solver USHAS (Unstructured Solver for Hypersonic Aerothermodynamics) is employed for the present study. To explore the feasibility of pulsed energy addition in reducing the wave drag at different flight conditions, flight Mach numbers of 5.75, 6.9 and 8.0 are chosen for the study. An [Formula: see text] apex angle blunt cone model is considered to be placed in such hypersonic streams, and steady-state drag and unsteady drag reductions are computed. The simulation results indicate that drag of the blunt-body can be reduced below the steady-state drag for a significant period of energy bubble-shock layer interaction, and the corresponding propulsive energy savings can be up to 9%. For energy pulse of magnitude 100mJ deposited to a spherical region of 2 mm radius, located 50 mm upstream of the blunt-body offered a maximum percentage of wave drag reduction in the case of Mach 8.0 flowfield. Two different flow features are found to be responsible for the drag reduction, one is the low-density core of the blast wave and the second one is the baroclinic vortex created due to the plasma energy bubble-shock layer interaction. For the same freestream stagnation conditions, these two flow features are noted to be very predominant in the case of high Mach number flow in comparison to Mach 5.75 and 6.9 cases. However, the ratio of energy saved to the energy consumed is noted as a maximum for the lower Mach number case.

Supersonic Bi-Directional Flying Wing Wave Drag Optimization Based on Alternative Form of CST Method

2013 ◽  
Vol 477-478 ◽  
pp. 240-245
Author(s):  
Xiaohui Guan
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Wave Drag ◽  
Alternative Form ◽  
Shape Transformation ◽  
Flat Bottom ◽  
Symmetric Configuration ◽  
Shape Parameterization ◽  
Wave Drag Reduction ◽  
Sufficient Precision

Bi-directional Flying Wing (BFW) is a new supersonic civil transport shape concept that aims to meet the conflict requirements of high speed cruise and low speed take-off/landing missions. In this paper the Class-Shape-Transformation (CST) shape parameterization method is modified to represent the BFW shape, and new basis functions suitable for the BFW airfoil representation are constructed. The Far-field Composite Element (FCE) wave drag optimization is performed on both the flat bottom and symmetric BFW configurations, and the drag reduction effects and result precision are surveyed. It is suggested that significant wave drag reduction can be achieved by the FCE optimization for both the flat bottom and the symmetric BFW configurations. The wave drag coefficients with sufficient precision can be obtained in the FCE optimization of the symmetric configuration; while the FCE optimization results of the flat bottom one are not accurate enough.

Effect of interfilament hydrodynamic interaction on swimming performance of two-filament microswimmers

Soft Matter ◽  
2018 ◽  
Vol 14 (37) ◽  
pp. 7748-7758 ◽  
Author(s):  
T. Sonamani Singh ◽  
Priyanka Singh ◽  
R. D. S. Yadava
Keyword(s):  
Hydrodynamic Interaction ◽  
Swimming Performance ◽  
Viscous Drag

The motion of two-filament artificial swimmers is modeled by assuming interfilament coupling via hydrodynamic viscous drag.

Wave drag reduction by means of aerospikes on transonic wings

Shock Waves ◽  
2009 ◽  
pp. 1309-1313 ◽  
Author(s):  
M. Rein ◽  
H. Rosemann ◽  
E. Schülein
Keyword(s):  
Drag Reduction ◽  
Wave Drag ◽  
Wave Drag Reduction

scholarly journals Drag Characteristics of Competitive Swimming Children and Adults

2008 ◽  
Vol 24 (1) ◽  
pp. 35-42 ◽  
Author(s):  
Per-Ludvik Kjendlie ◽  
Robert Keig Stallman
Keyword(s):  
Perturbation Method ◽  
Froude Number ◽  
Wave Drag ◽  
Maximal Velocity ◽  
Evaluation Tool ◽  
Competitive Swimming ◽  
Velocity Decay ◽  
Competitive Swimmers ◽  
Drag Factor ◽  
Swimming Technique

The aims of this study were to compare drag in swimming children and adults, quantify technique using the technique drag index (TDI), and use the Froude number (Fr) to study whether children or adults reach hull speed at maximal velocity (vmax). Active and passive drag was measured by the perturbation method and a velocity decay method, respectively, including 9 children aged 11.7 ± 0.8 and 13 adults aged 21.4 ± 3.7. The children had significantly lower active (kAD) and passive drag factor (kPD) compared with the adults. TDI (kAD/kPD) could not detect any differences in swimming technique between the two groups, owing to the adults swimming maximally at a higher Fr, increasing the wave drag component, and masking the effect of better technique. The children were found not to reach hull speed atvmax, and their Fr were 0.37 ± 0.01 vs. the adults 0.42 ± 0.01, indicating adults’ larger wave-making component of resistance atvmaxcompared with children. Fr is proposed as an evaluation tool for competitive swimmers.

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