James J. Allen

Roughness effects in turbulent pipe flow

Mean flow measurements are presented for fully developed turbulent pipe flow over a Reynolds number range of

Thrust efficiency of harmonically oscillating flexible flat plates

57,{times},10^3

Scaling and instability of a junction vortex

to

Evaluation of a universal transitional resistance diagram for pipes with honed surfaces

21,{times},10^6

Vortex interaction with a moving sphere

where the flow exhibits hydraulically smooth, transitionally rough, and fully rough behaviours. The surface of the pipe was prepared with a honing tool, typical of many engineering applications, achieving a ratio of characteristic roughness height to pipe diameter of 1 : 17000. Results for the friction factor show that in the transitionally rough regime this surface follows a Nikuradse (1933)-type inflectional relationship rather than the monotonic Colebrook (1939) relationship used in the Moody diagram. This result supports previous suggestions that the Moody diagram in the transitional regime must be used with caution. Outer scaling of the mean velocity data shows excellent collapse and strong evidence for Townsends outer layer similarity hypothesis for rough-walled flows. Finally, the pipe exhibited smooth behaviour for scaled roughness height

Further support for Townsend’s Reynolds number similarity hypothesis in high Reynolds number rough-wall pipe flow

k_s^+ ,{le}, 3.5

Transition processes for junction vortex flow

, which supports the suggestion by Zagarola & Smits (1998) that their pipe was hydraulically smooth for

Modification of the large-scale features of high Reynolds number wall turbulence by passive surface obtrusions

Re_D,,{leq}, 24,{times},10^6

Piezoelectric Eels For Energy Harvesting In the Ocean

.

Two‐dimensional compact finite difference immersed boundary method

We consider the efficiency of thrust-producing inextensible membranes with variable bending rigidities. The present study is a numerical investigation of the thrust generation and flow-field characteristics of a two-dimensional flapping flexible membrane, fixed at its leading edge. To study the time-dependent response of the membranes, a fluid/structure solver that couples a compact finite-difference immersed boundary method flow solver with a thin-membrane structural solver was developed. Using a body-fitted grid, external forcing to the structure is calculated from the boundary fluid dynamics. A systematic series of runs of the fluid/structure solver was performed in order to obtain a clear picture of the thrust-producing characteristics of membranes with bending rigidities ranging between EI = 5 × 10 −6 and EI = 2 × 10 −5 and structural mass coefficients between ρ s h = 0.01 and ρ s h = 0.04, for a Reynolds number of Re = 851.