Discussions: (1) “On the Axisymmetric Turbulent Boundary Layer Growth Along Long Thin Circular Cylinders,â€‌ (Jordan, S. A., 2014, ASME J. Fluids Eng., 136(5), p. 051202) and (2) “Understanding Tow Tank Measurements of Total Drag for Long Thin Circular Cylinders,â€‌ (Jordan, S. A., 2014, ASME J. Fluids Eng., 136(3), p. 031205)

Abstract

In a recent paper, work of Jordan [1] has pointed out that “measurements of Lueptow et al. [2] did not confirm the empirical expression خ´/a=0.45(x/a)0.746 proposed by Afzal and Singh [3], but however supports the general consensus that the loglayer parameters converged to those of the flat plate as خ´/a regardless of the specific flow conditions.â€‌ Lueptow et al. [2] also pointed out that the boundary layer thickness does not grow according to the law خ´/a=0.045(x/a)0.746 proposed by Afzal and Singh [3]; see also Lueptow [4]. The discussion arose without any comparison with the data [1,2,4], who also ignored the fact that this relation of Afzal and Singh [3] under question was proposed for one value of Reynolds number Rea = 14,200. The main parameter is خ´/a and various Reynolds numbers are Rex=Uex/خ½,Rea=Uea/خ½ and a+=aUد„/خ½. Here خ´ is the boundary layer thickness due to uniform free stream velocity Ue in streamwise xdirection for flow along a long cylinder of radius a and length L. For axisymmetric turbulent boundary layer growth along thin long circular cylinder the data of Lueptow et al. [2]. Afzal and Singh [3] and Rao and Keshavan [5] were compared in Fig. 14(a) of Jordan [1] with his empirical expression (2), but ignored his own [6] simultaneous previous prediction (7) from citation in Jordan [1]. The aim of this discussion is to consider the correlation (1) due to Afzal and Singh [3] in this communication.