Author

# Özgür Ertunç

Other affiliations: University of Diyala, University of Erlangen-Nuremberg

Bio: Özgür Ertunç is an academic researcher from Özyeğin University. The author has contributed to research in topics: Turbulence & Reynolds number. The author has an hindex of 9, co-authored 51 publications receiving 288 citations. Previous affiliations of Özgür Ertunç include University of Diyala & University of Erlangen-Nuremberg.

Topics: Turbulence, Reynolds number, Reynolds stress, Pipe flow, Wind tunnel

##### Papers published on a yearly basis

##### Papers

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TL;DR: In this paper, the authors investigated the inhomogeneity of turbulence generated by static grids with the help of hot-wire measurements in a wind-tunnel and direct numerical simulations based on the Lattice Bolztmann method.

Abstract: Homogeneity of turbulence generated by static grids is investigated with the help of hot-wire measurements in a wind-tunnel and direct numerical simulations based on the Lattice Bolztmann method. It is shown experimentally that Reynolds stresses and their anisotropy do not become homogeneous downstream of the grid, independent of the mesh Reynolds number for a grid porosity of 64 %, which is higher than the lowest porosities suggested in the literature to realize homogeneous turbulence downstream of the grid. In order to validate the experimental observations and elucidate possible reasons for the inhomogeneity, direct numerical simulations have been performed over a wide range of grid porosity at a constant mesh Reynolds number. It is found from the simulations that the turbulence wake behind the symmetric grids is only homogeneous in its mean velocity but is inhomogeneous when turbulence quantities are considered, whereas the mean velocity field becomes inhomogeneous in the wake of a slightly non-uniform grid. The simulations are further analysed by evaluating the terms in the transport equation of the kinetic energy of turbulence to provide an explanation for the persistence of the inhomogeneity of Reynolds stresses far downstream of the grid. It is shown that the early homogenization of the mean velocity field hinders the homogenization of the turbulence field.

49 citations

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TL;DR: In this article, a combined analytical and experimental investigation of sinusoidal mass flow-controlled, pulsating, laminar and fully developed pipe flow was carried out, where the equations describing such flows were normalized to allow for a general solution, depending only on the normalized amplitude mA* of the mass flow pulsation and the normalized frequency F.

45 citations

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TL;DR: In this paper, mass flow rate driven, laminar, fully developed pulsating pipe flow has been studied experimentally, analytically and numerically, and results of experimental investigations are presented and are complemented by data deduced from corresponding analytical and numerical studies.

Abstract: Pressure gradient driven, laminar, fully developed pulsating pipe flows have been extensively studied by various researchers and the data for the resultant flow field are available in a number of publications. The present paper, however, concentrates on related flows that are mass flow driven, i.e., the flows where the mass flow rate is prescribed as m=mM+mAfm(t) and fm(t) is periodically varying in time. Sinusoidal and triangular mass flow rate pulsations in time are analytically considered in detail. Results of experimental investigations are presented and are complemented by data deduced from corresponding analytical and numerical studies. Overall, the results provide a clear insight into mass flow rate driven, laminar, fully developed pulsating pipe flow. To the best of the authors’ knowledge, flows of this kind have not been studied before experimentally, analytically and numerically.

44 citations

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TL;DR: It is shown that two reversal locations away from the wall can occur in pulsating flows in pipes and channels and the reversed amount of mass per period reaches a maximum at a certain dimensionless frequency for a given amplitude of mass-flow rate fluctuations.

Abstract: Analytical investigations are carried out on pulsating laminar incompressible fully developed channel and pipe flows. An analytical solution of the velocity profile for arbitrary time-periodic pulsations is derived by approximating the pulsating flow variables by a Fourier series. The explicit interdependence between pulsations of velocity, mass-flow rate, pressure gradient, and wall shear stress are shown by using the proper dimensionless parameters that govern the flow. Utilizing the analytical results, the scaling laws for dimensionless pulsation amplitudes of the velocity, mass-flow rate, pressure gradient, and wall shear stress are analyzed as functions of the dimensionless pulsation frequency. Special attention has been given to the scaling laws describing the flow reversal phenomenon occurring in pulsating flows, such as the condition for flow reversal, the dependency of the reversal duration, and the amplitude. It is shown that two reversal locations away from the wall can occur in pulsating flows in pipes and channels and the reversed amount of mass per period reaches a maximum at a certain dimensionless frequency for a given amplitude of mass-flow rate fluctuations. These analyses are numerically conducted for pipe and channel flows over a large frequency range in a comparative manner.

20 citations

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TL;DR: In this article, an extension of a classical analytical model for separation efficiency is proposed that accounts for the contributions provided by straight wall sections, and the extension of the analytical model is benchmarked against experiments performed by Leber (2003) on a single stage straight vane separator.

19 citations

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IBM

^{1}TL;DR: Damascene copper electroplating for on-chip interconnections, a process that was conceived and developed in the early 1990s, makes it possible to fill submicron trenches and vias with copper without creating a void or a seam and has thus proven superior to other technologies of copper deposition as discussed by the authors.

Abstract: Damascene copper electroplating for on-chip interconnections, a process that we conceived and developed in the early 1990s, makes it possible to fill submicron trenches and vias with copper without creating a void or a seam and has thus proven superior to other technologies of copper deposition. We discuss here the relationship of additives in the plating bath to superfilling, the phenomenon that results in superconformal coverage, and we present a numerical model which accounts for the experimentally observed profile evolution of the plated metal.

1,006 citations

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TL;DR: The paper is a review in the very broadest sense of the word, written with the purpose of orienting the interested newcomer to the field of electroporation applications in food technology towards the pertinent, highly relevant and more in-depth literature from the respective subdomains of Electroporation research.

Abstract: Electroporation is a method of treatment of plant tissue that due to its nonthermal nature enables preservation of the natural quality, colour and vitamin composition of food products. The range of processes where electroporation was shown to preserve quality, increase extract yield or optimize energy input into the process is overwhelming, though not exhausted; e.g. extraction of valuable compounds and juices, dehydration, cryopreservation, etc. Electroporation is—due to its antimicrobial action—a subject of research as one stage of the pasteurization or sterilization process, as well as a method of plant metabolism stimulation. This paper provides an overview of electroporation as applied to plant materials and electroporation applications in food processing, a quick summary of the basic technical aspects on the topic, and a brief discussion on perspectives for future research and development in the field. The paper is a review in the very broadest sense of the word, written with the purpose of orienting the interested newcomer to the field of electroporation applications in food technology towards the pertinent, highly relevant and more in-depth literature from the respective subdomains of electroporation research.

202 citations

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TL;DR: In this article, a new experimental investigation of decaying turbulence generated by a low-blockage space-filling fractal square grid is presented, where the authors find agreement with previous works by Seoud & Vassilicos (2007) and Mazellier et al. (2010) but also extend the length of the assessed decay region and consolidate the results by repeating the experiments with different probes of increased spatial resolution.

Abstract: A new experimental investigation of decaying turbulence generated by a low-blockage space-filling fractal square grid is presented. We find agreement with previous works by Seoud & Vassilicos (2007) and Mazellier & Vassilicos (2010) but also extend the length of the assessed decay region and consolidate the results by repeating the experiments with different probes of increased spatial resolution. It is confirmed that this moderately high Reynolds number Re{\lambda} turbulence (up to Re{\lambda} {\simeq}350 here) does not follow the classical high Reynolds number scaling of the dissipation rate {\epsilon} ~ u'^3/L and does not obey the equivalent proportionality between the Taylor-based Reynolds number Re{\lambda} and the ratio of integral scale L to Taylor micro-scale {\lambda}. Instead we observe an approximate proportionality between L and {\lambda} during decay. This non-classical behaviour is investigated by studying how the energy spectra evolve during decay and examining how well they can be described by self-preserving single-length scale forms. A detailed study of homogeneity and isotropy is also presented which reveals the presence of transverse energy transport and pressure transport in the part of the turbulence decay region where we take data (even though previous studies found mean flow and turbulence intensity profiles to be approximately homogeneous in much of the decay region). The exceptionally fast turbulence decay observed in the part of the decay region where we take data is consistent with the non-classical behaviour of the dissipation rate. Measurements with a regular square mesh grid as well as comparisons with active grid experiments by Mydlarski & Warhaft (1996) and Kang, Chester & Meveneau (2003) are also presented to highlight the similarities and differences between these turbulent flows and the turbulence generated by our fractal square grid.

157 citations

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TL;DR: In this article, a new experimental investigation of decaying turbulence generated by a low-blockage space-filling fractal square grid is presented, and it is confirmed that this moderately high Reynolds number turbulence does not follow the classical high Reynolds numbers scaling of the dissipation rate and does not obey the equivalent proportionality between the Taylor-based Reynolds number and the ratio of integral scale to the Taylor microscale.

Abstract: A new experimental investigation of decaying turbulence generated by a low-blockage space-filling fractal square grid is presented. We find agreement with previous works by Seoud & Vassilicos (Phys. Fluids, vol. 19, 2007, 105108) and Mazellier & Vassilicos (Phys. Fluids, vol. 22, 2010, 075101) but also extend the length of the assessed decay region and consolidate the results by repeating the experiments with different probes of increased spatial resolution. It is confirmed that this moderately high Reynolds number turbulence (up to here) does not follow the classical high Reynolds number scaling of the dissipation rate and does not obey the equivalent proportionality between the Taylor-based Reynolds number and the ratio of integral scale to the Taylor microscale . Instead we observe an approximate proportionality between and during decay. This non-classical behaviour is investigated by studying how the energy spectra evolve during decay and examining how well they can be described by self-preserving single-length-scale forms. A detailed study of homogeneity and isotropy is also presented which reveals the presence of transverse energy transport and pressure transport in the part of the turbulence decay region where we take data (even though previous studies found mean flow and turbulence intensity profiles to be approximately homogeneous in much of the decay region). The exceptionally fast turbulence decay observed in the part of the decay region where we take data is consistent with the non-classical behaviour of the dissipation rate. Measurements with a regular square mesh grid as well as comparisons with active-grid experiments by Mydlarski & Warhaft (J. Fluid Mech., vol. 320, 1996, pp. 331–368) and Kang, Chester & Meveneau (J. Fluid Mech., vol. 480, 2003, pp. 129–160) are also presented to highlight the similarities and differences between these turbulent flows and the turbulence generated by our fractal square grid.

127 citations

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TL;DR: SDT-based composite nanoplatforms harvest the most substantially enhanced inhibitory consequences against primary and metastatic tumors, which, thus, provide a profound attribute for T cell-based immunotherapy against tumor.

116 citations