Peter Monkewitz

Biographie

After graduating in physics from the Swiss Federal Institute of Technology in Zurich, he received his Ph.D. from the same institution in 1977 with a thesis on internal acoustics. From 1977-80 he was a research associate in the Aerospace Department of the Univ. of Southern California in Los Angeles, where he worked experimentally and theoretically on jet noise and hydrodynamic instabilities. In 1980 he joined the faculty of the School of Engineering at UCLA where he made research contributions in several areas. In the field of hydrodynamic instability he had a hand in the popularization of the concept of absolute instability in fluid mechanics, the development of the concept as well as of the asymptotic analytical description of global modes in nonparallel flows, and in the modelling of vortex shedding from bluff bodies. Other areas of research include internal acoustics, jet mixing, in particular in low-density jets in which he co-discovered enhanced mixing by "side-jets," flow control, transition to turbulence, turbulence and, most recently, flame instabilities. In 1988 he was awarded the Humboldt prize and spent the academic year 1989/90 as Humboldt awardee at the Technical University in Berlin. In 1992 he was elected Fellow of the American Physical Society. Since 1993 he holds the chair for experimental fluid mechanics and heads the Laboratory of Fluid Mechanics (LMF) of the Swiss Federal Institute of Technology in Lausanne (EPFL), Switzerland. He has been Chairman of its Mechanical Engineering Department from July 1997 to December 2000, co-organizer of the 1999 Research programme on turbulence at the Isaac Newton Institute in Cambridge, UK, Associate Editor of the Journal of Fluid Mechanics from 1995 to 2000 and a member of the EUROMECH Council. He is currently an Associate Editor of Physics of Fluids , a member of the IUTAM general assembly, a member of the schoolwide EPFL Academic Promotions Committee and part-time "program monitor" for the Swiss National Science Foundation (member of its Research Council).

Official source

https://people.epfl.ch/peter.monkewitz?lang=fr

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Uncertainty Analysis of the Von Karman Constant for the Mean Centerline Velocity in CICLoPE

Peter Monkewitz

Further examination of the pressure measurement uncertainties in determining the pressure gradient along the fully-developed section of CICLoPE, yields a Karman constant based on the centerline velocity of kappa(CL) = 0.43 +/- 0.06. More significantly, we conclude that the CICLoPE facility requires a more accurate pressure scanning method for determining dp/dx; e.g., using a Scanivalve connected to a single more accurate pressure transducer.

SPRINGER INTERNATIONAL PUBLISHING AG2019

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Katabatic Flow: A Closed-Form Solution with Spatially-Varying Eddy Diffusivities

Jiannong Fang, Marco Giovanni Giometto, Peter Monkewitz, Marc Parlange

The Nieuwstadt closed-form solution for the stationary Ekman layer is generalized for katabatic flows within the conceptual framework of the Prandtl model. The proposed solution is valid for spatially-varying eddy viscosity and diffusivity (O'Brien type) and constant Prandtl number (Pr). Variations in the velocity and buoyancy profiles are discussed as a function of the dimensionless model parameters and , where is the hydrodynamic roughness length, is the Brunt-Vaisala frequency, is the surface sloping angle, is the imposed surface buoyancy, and is a reference velocity scale used to define eddy diffusivities. Velocity and buoyancy profiles show significant variations in both phase and amplitude of extrema with respect to the classic constant model and with respect to a recent approximate analytic solution based on the Wentzel-Kramers-Brillouin theory. Near-wall regions are characterized by relatively stronger surface momentum and buoyancy gradients, whose magnitude is proportional to and to . In addition, slope-parallel momentum and buoyancy fluxes are reduced, the low-level jet is further displaced toward the wall, and its peak velocity depends on both and .

Springer Verlag2017

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The trinity of so-called "canonical" wall-bounded turbulent flows, comprising the zero pressure gradient turbulent boundary layer, abbreviated ZPG TBL, turbulent pipe flow, and channel/duct flows has continued to receive intense attention as new and more reliable experimental data have become available. Nevertheless, the debate on whether the logarithmic part of the mean velocity profile, in particular the Karman constant kappa, is identical for these three canonical flows or flow-dependent is still ongoing. In this paper, the asymptotic matching requirement of equal. in the logarithmic overlap layer, which links the inner and outer flow regions, and in the expression for the centerline/free-stream velocity is reiterated and shown to preclude a universal logarithmic overlap layer in the three canonical flows. However, the majority of pipe and channel flowstudies at friction Reynolds numbers Re-tau below approximate to 10(4) extract from near-wall profiles the same kappa of 0.38-0.39 as in the ZPG TBL. This apparent contradiction is resolved by a careful reanalysis of high-quality mean velocity profiles in the Princeton "Superpipe" and other pipes, channels, and ducts, which shows that the mean velocity in a near-wall region extending to around 700 "+" units in channels and ducts and 500 "+" units in pipes is the same as in the ZPG TBL. In other words, all the "canonical" flow profiles contain the lower end of the ZPG TBL log-region, which starts at a wall distance of 150-200 "+" units with a universal kappa of kappa(ZPG) approximate to 0.384. This interior log-region is followed by a second logarithmic region with a flow specific. > kappa(ZPG), which increases monotonically with pressure gradient. This second, exterior log-layer is the actual overlap layer matching up to the outer expansion, which implies equality of the exterior. and kappa(CL) obtained from the evolution of the respective centerline velocity with Reynolds number. The location of the switch-over point implies furthermore that this second log-layer only becomes clearly identifiable, i.e., separated from the wake region, for Re-tau well beyond 10(4) (see Fig. 1). This explains the discrepancies between the Karman constants of 0.38-0.39, extracted from near-wall pipe profiles below Re-tau approximate to 10(4) and the kappa's obtained from the evolution of the centerline velocity with Reynolds number. The same analysis is successfully applied to velocity profiles in channels and ducts even though experiments and numerical simulations have not yet reached Reynolds numbers where the different layers have even started to clearly separate.

Amer Physical Soc2017

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Amer Physical Soc2017