Wake of a Self-Propelled Body, Part 1: Momentumless Wake

Abstract

Experiments were performed in the turbulent boundary layer and near wake of an axisymmetric body propelled by a jet to study the evolution of the momentumless wake. Comparisons with measurements in the drag wake of the body (without the jet) and in the isolated jet provide an understanding of initial mixing between the two ows. Triple-sensor hot wires and multitube pressure probes were used to measure the mean velocity, turbulence, and pressure elds from the jet exit to a distance of over 15 jet diameters. It is found that the evolution of the wake takes place in three distinct stages: a zone close to the jet exit, about 4 jet diameters long, where the jet shear layer mixes with uid from the wall region of the boundary layer; an intermediate region, about 12 jet diameters long, where there is mixing between the boundary layer and the jet up to the axis; and the third region where the two ows lose their identities to become a single shear layer and the mean ow acquires some of the characteristics of self-similar ows. However, the momentumless wake does not conform to the assumptions and results of classical similarity analysis.

Numerical modelling of momentumless wakes using semiempirical turbulence models of second and third order

“…Brought to you by | Florida International University Libraries Authenticated Download Date | 6/13/15 9:17 AM Comparison of computational data (model 3 G1 and G2) with laboratory experiment data[1] on turbulent wake dynamics behind a sphere. We found that the downstream turbulent energy e 0 at large distances from the body changes by the power law e 0 x1 44 , which is in rather good agreement with the known experimental and numerical data, including: x 1 6[45], x 1 455[16], x 1 46[19], x 1 5[18], x10 7 The calculations were carried out by simplified model 3 in which we assumed U d 0 at distances from 10 to 2000 body diameters.…”

Quantitative analysis of tethered and free-swimming copepodid flow fields

“…[Note that an equally valid description of this phenomenon has been made with regard to a 'momentumless wake' for a self-propelled object (e.g. Naudascher, 1965;Sirviente and Patel, 2000). The term 'momentumless wake' refers to the momentum distribution in the wake of the self-propelled object having the same momentum flux as the approaching flow upstream of the object.…”

Modification of a Circular Cylinder Near Wake by a Rectangular Jet

“…More recently, Serviente and Patel 3 have measured mean and turbulentvelocity pro les behind an axisymmetric self-propelled body at various locations downstream of the jet nozzle. Several investigatorshave utilized less streamlined shapes as sources for the rear jet.…”

“…In their work, contact deformationwas considered,and an analyticfunctiondescribing it was proposed and incorporated into the analysis. Recently, Gong et al 3 presented solutions for the problems of functionally graded material (FGM) cylindrical shells subjected to low-velocity impact, and Gong and Lam 4 examined the effects of structural damping on impact response.…”