Kelvin wake pattern at large Froude numbers. (10th January 2014)

• Record Type: Journal Article
• Authors: Darmon, Alexandre; Benzaquen, Michael; Raphaël, Elie
• Is Part Of: Journal of fluid mechanics. Volume 738(2014:Jan.)
• Publication Date: 2014-01-10
• Subjects: Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2013.607
• Languages: English
• ISSNs: 0022-1120

Abstract

<abstract abstract-type="normal"> <title>Abstract</title> <p>Gravity waves generated by an object moving at constant speed at the water surface form a specific pattern commonly known as the Kelvin wake. It was proved by Lord Kelvin that such a wake is delimited by a constant angle <inline-formula><alternatives><inline-graphic xlink:href="ark:/27927/pgg43kn1pcz" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><tex-math><![CDATA[${\simeq }19. 4{7}^{\circ } $]]></tex-math></alternatives></inline-formula>. However a recent study by Rabaud and Moisy based on the observation of airborne images showed that the wake angle seems to decrease as the Froude number <inline-formula><alternatives><inline-graphic xlink:href="ark:/27927/pgg43kn1pgm" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><tex-math><![CDATA[$Fr$]]></tex-math></alternatives></inline-formula> increases, scaling as <inline-formula><alternatives><inline-graphic xlink:href="ark:/27927/pgg43kn1pjq" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><tex-math><![CDATA[$F{r}^{- 1} $]]></tex-math></alternatives></inline-formula> for large Froude numbers. To explain such observations they make the strong hypothesis that an object of size <inline-formula><alternatives><inline-graphic xlink:href="ark:/27927/pgg43kn1ph5" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><tex-math><![CDATA[$b$]]></tex-math></alternatives></inline-formula> cannot generate wavelengths larger than <inline-formula><alternatives><inline-graphic xlink:href="ark:/27927/pgg43kn1pf2" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><tex-math><![CDATA[$b$]]></tex-math></alternatives></inline-formula>. Without the need of such an assumption and modelling the moving object by an axisymmetric pressure field, we analytically show that the angle corresponding to the maximum amplitude of the waves scales as <inline-formula><alternatives><inline-graphic xlink:href="ark:/27927/pgg43kn1pbd" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><tex-math><![CDATA[$F{r}^{- 1} $]]></tex-math></alternatives></inline-formula> for large Froude numbers, whereas the angle delimiting the wake region outside which the surface is essentially flat remains constant and equal to the Kelvin angle for all <inline-formula><alternatives><inline-graphic xlink:href="ark:/27927/pgg43kn1pdh" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><tex-math><![CDATA[$Fr$]]></tex-math></alternatives></inline-formula>.</p> </abstract>