Naseem Uddin

Universiti Teknologi Brunei

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Bernhard Weigand

University of Stuttgart

Usman Allauddin

NED University of Engineering and Technology

Sven Olaf Neumann

Fachhochschule Kiel

Waqar A. Khan

Saveetha University

Bassam A. Younis

Taif University

S. O. Neumann

University of Calgary

Mahrukh Mahrukh

NED University of Engineering and Technology

Hafiz Mohammad Usman Khan

Jain University

M. Ehtesham-ul Haque

NED University of Engineering and Technology

Rafay Mohiuddin

Technical University of Munich

Cooperative Institutions

NED University of Engineering and Technology

Polytechnic University of Turin

University of Stuttgart

Universiti Teknologi Brunei

University of Lahore

National University of Sciences and Technology

University of Malaya

Samudra University

École Polytechnique Fédérale de Lausanne

Taibah University

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Heat Conduction Analysis Using the Finite Difference Technique

CRC Press eBooks (2023)

Naseem Uddin

Finite difference

10.1201/9781003428404-6

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Citations (0)

Forced Convection on Curved Surfaces and on an impact

CRC Press eBooks (2023)

Naseem Uddin

Forced convection

10.1201/9781003428404-10

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Thermal & Flow Field Analysis of Turbulent Swirling Jet Impingement Using Large Eddy Simulation

Springer eBooks (2009)

Naseem Uddin Sven Olaf Neumann Peter Lammers Bernhard Weigand

Large-Eddy Simulation

10.1007/978-3-540-88303-6_22

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Citations (4)

Applications of the Second Law of Thermodynamics

CRC Press eBooks (2024)

Naseem Uddin

10.1201/9781003423140-8

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Turbulence modeling of complex flows in CFD

Naseem Uddin

In the last two decades of the 20th century, the world had witnessed the enormous increase in the computational resources. This has brought in the tremendous increase in human knowledge and understanding of complex phenomenon, like turbulence and its modeling among others. The technical development has brought new challenges in engineering design. Whether we limit ourselves to the earthly matters or indulge in space exploration, the simulation of turbulence has become a routine task. Turbulence is a phenomenon in nature comprising of complex eddy structures which can greatly improve heat and mass transfer. The simplistic approach for the computation of turbulent flows is to compute them by Reynolds Averaged Navier-Stokes (RANS) equations based models. But due to the averaging procedure, the inherent unsteadiness of the flow is compromised. On the other hand, Direct Numerical Simulation (DNS) is the best approach for turbulent flow computations, in which no modeling assumptions are invoked and turbulent eddies as small as of the order of Kolmogorov scale are computed. The middle approach between these extremes is the Large Eddy Simulation (LES), in which part of the turbulence is modeled and rest is computed. However, the computational costs and memory requirement are still too large to take it as a general purpose engineering design tool. In this thesis, the effect of changes in inflow conditions on the heat transfer by an impinging jet is investigated using LES. The Dynamic Smagorinsky model proposed by Germano et al. has been used as a subgrid model. Results of several Large Eddy Simulations are reported in the thesis, which are conducted with use of total 244 processors on high performance computing clusters. The inflow conditions explored are: - The fully developed turbulent jet - Swirling jet - Velocity field active excitation - Velocity field passive excitation - Temperature field excitation An ERCOFTAC recommended benchmark test case of an orthogonally impinging round jet at Reynolds number of 23000 is simulated first. The agreement between the experiments and the LES gives encouragement for further investigations. Therefore in a next step, the effect of inlet velocity and temperature fields excitations of an orthogonally impinging round jet, on the heat transfer are explored. In case of the active control of the impinging jet’s inlet velocity field, it is found that the selection of excitational frequencies is important for heat transfer enhancement. The excitation at the subharmonic frequencies of the preferred mode is found to be a promising approach for heat transfer enhancement. A passively excited inlet velocity field is also investigated. It is found that this approach gives a better heat transfer than an active excitation case. The novel idea of heat transfer enhancement through jet’s inlet temperature field excitation is presented. The LES shows that the excitation at the preferred mode can give surface averaged Nusselt number higher than the non-excited jet impingement case. However the frequencies higher than the preferred mode should be taken with care, as they might cause thermal fatigue. The effect of the addition of the swirl to the impinging jet on the heat transfer is investigated. Also, it is found that the swirl does not give appreciable enhancement in heat transfer for H=D=2 case. The knowledge of flow and passive scalar flux dynamics gained through the simulation has helped in understanding the functional relationship between different turbulence quantities and heat transfer. It is found that the assumption of a constant turbulent Prandtl number (often used in RANS based models) is not a realistic approach. Alternative is to use scalarflux models, which allow the prediction of scalar-fluxes in non-isotropic turbulent state. The knowledge gained through the LES is then used to investigate coefficients in some explicit scalar-flux models (RANS based models). The investigation gives insight in the impingement phenomenon, which could help in the development of advanced turbulence models for heat transfer prediction. Die 80er- und 90er-Jahren des 20. Jahrhunderts waren gekennzeichnet durch eine enorme Steigerung des Leistungsvermogens von Computern. Diese Entwicklung fuhrte dazu, dass komplexe Phanomene, wie z.B. Turbulenz und ihre Modellierung nun sehr viel besser verstanden werden. Diese technische Entwicklung halt auch neue Herausforderungen fur Ingenieure bereit. Ob man sich auf Vorgange auf der Erde beschrankt, oder den Weltraum erkundet: die Simulation von Turbulenz ist zu einer Routineaufgabe geworden. Turbulenz ist ein Naturphanomen. Sie besteht aus komplexen Wirbelstrukturen, die den Impuls-, Warme- und Stofftransport stark verbessern konnen. Der einfachste Weg, turbulente Stromungen zu berechnen, ist, sie mit Hilfe der Reynolds-gemittelten Navier-Stokes Gleichungen (RANS) zu modellieren. Allerdings wird hierbei das systemimmanente instationare Verhalten der Stromung geglattet. Dahingegen liefert die Direkte Numerische Simulation (DNS) die genauesten Resultate bei der Simulation turbulenter Stromungen. Bei diesem Verfahren werden keinerlei vereinfachende Modelle verwendet und kleinste turbulente Wirbel bis zur Kolmogorov-Grosenordnung werden berechnet. Einen Mittelweg zwischen diesen beiden Ansatzen stellt die Large Eddy Simulation (LES) dar, bei der nur ein Teil der turbulenten Strukturen aufgelost und der Rest modelliert wird. Trotz dieser Vereinfachung sind die Kosten und der Speicheraufwand dieser Methode immer noch zu hoch, um sie fur Ingenieursanwendungen zu einem Standardwerkzeug werden zu lassen. In dieser Arbeit wird die LES-Methode benutzt, um die Auswirkung von Veranderungen der Eintrittsbedingungen auf den Warmeubergang eines Prallstrahls zu untersuchen. Das dynamische Smagorinsky-Modell von Germano et al. wurde als Subgrid-Modell verwendet. Die Ergebnisse von mehreren LES-Rechnungen, die auf 244 Prozessorkernen auf Hochleistungsrechnern durchgefuhrt wurden, werden dargestellt. Die verschiedenen untersuchten Eintrittsbedingungen sind: - voll ausgebildeter turbulenter Strahl - drallbehafteter Strahl - aktiv angeregtes Geschwindigkeitsfeld - passiv angeregtes Geschwindigkeitsfeld - angeregtes Temperaturfeld Zunachst wird ein ERCOFTAC Benchmark-Testfall eines senkrechten kreis formigen Prallstrahls mit der Reynoldszahl 23.000 simuliert. Die gute Ubereinstimmung zwischen den Experimenten und der LES-Rechnung ist die Grundlage fur die folgenden Untersuchungen. Im nachsten Schritt wird der Einfluss der Anregung von Geschwindigkeits- und Temperaturfeld auf den Warmeubergang bestimmt. Fur den Fall der aktiven Anregung des Geschwindigkeitsfeldes im Strahleintritt stellt sich heraus, dass die Wahl der Anregungsfrequenz wichtig ist fur die Intensivierung des Warmeubergangs. Eine Anregung mit subharmonischen Frequenzen der bevorzugten Mode erweist sich als vielversprechend. Ein passiv angeregtes Geschwindigkeitsfeld wird ebenfalls untersucht. Der Warmebergang ist gegenuber der aktiven Anregung verbessert. Eine neuartige Idee der Warmeubergangssteigerung durch Anregung des Geschwindigkeitsfeldes beim Strahleintritt wird prasentiert. Die LES zeigt, dass die Anregung bei der bevorzugten Mode die flachengemittelte Nusseltzahl im Vergleich zum nicht angeregten Fall steigert. Allerdings ist Vorsicht geboten bei der Auswahl von Anregungsfrequenzen, die hoher sind als die bevorzugte Mode, da sie thermische Ermudung hervorrufen konnen. Zusatzlich wird die Auswirkung der Strahlverwirbelung auf den Warmeubergang untersucht. Daruber hinaus wird festgestellt, dass die Verwirbelung den Warmeubergang fur H/D=2 nicht nennenswert steigert. Die durch diese Simulationen gewonnenen Kenntnisse der Stromungsmechanik und der passiven Skalarflusse sind hilfreich fur das Verstandnis des funktionalen Zusammenhangs zwischen verschiedenen Turbulenzgrosen und dem Warmeubergang. Die Annahme einer konstanten turbulenten Prandtlzahl (wie sie oft in RANS-Modellen Anwendung findet) ist vielfach nicht realistisch. Alternativ empfiehlt es sich, Skalarfluss-Modelle zu verwenden, die eine Vorhersage der Skalarflusse in anisotroper Turbulenz erlauben. Das mit Hilfe der LES-Rechnungen gewonnene Verstandnis wird benutzt, um die Koeffizienten in einigen expliziten (RANS basierten) Skalarfluss-Modellen zu analysieren. Die Untersuchung vermittelt einen Einblick in das Verhalten eines Prallstrahls, was fur die weitere Entwicklung von Turbulenzmodellen fur die Simulation des Warmeubergangs hilfreich sein kann.

10.18419/opus-3781

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Citations (16)

Heat and mass transport in an electrically conducting nanofluid flow over two-dimensional geometries

Heliyon (2023)

Usman Usman Waqar A. Khan Naseem Uddin Taseer Muhammad

Engineering equipment in medicine, chemical and power engineering, electronics, and other human endeavours use nanofluids. The ability to improve mass and heat transport because of the low concentration of nanoparticles is the primary driver behind the vast array of nanofluid applications. Thus, the famous problems of viscous, incompressible, Newtonian, and 2-D laminar flow are revisited to investigate the mass and heat transmission rates for water-based carbon nanotubes (CNTs) with variable magnetic fields and external pressure gradients. Flow cases considered with varying pressure gradients are the flows upon a flat plate, flow in a planar diverging and converging channel, flow over a wedge, and plane stagnation flows, which are investigated. The impressions of thermophoresis and Brownian motion parameters are examined through the Buongiorno model. Using the Görtler transformation, the leading boundary layer (BL) equations are converted into dimensionless forms of ordinary differential equations (ODEs). Runge-Kutta Fehlberg Method (RKF45) is operated to tackle the ensuing ODEs to find the mass, heat, and skin friction rates. It has been found that the rates of shear stress, mass, and heat transport slow down with an escalating magnetic field. Although mass transport rates are decreased, shear stress and heat transport (HT) rates escalate due to the solid volume portion of carbon nanotubes. Furthermore, the pressure gradient parameter facilitates faster heat and shear stress transmission rates.

Thermophoresis

Pressure gradient

Mass flow

10.1016/j.heliyon.2023.e18377

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Citations (7)

Kinematics of Fluid Particle

CRC Press eBooks (2022)

Naseem Uddin

Particle (ecology)

10.1201/9781003315117-3

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Viscous Flow through Conduits

CRC Press eBooks (2022)

Naseem Uddin

Electrical conduit

10.1201/9781003315117-10

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Heat and mass transfer from a suddenly moved plate in nanofluids

Proceedings of the Institution of Mechanical Engineers Part N Journal of Nanoengineering and Nanosystems (2012)

Naseem Uddin Waqar A. Khan Mahmood Rahi

Stokes’ first problem is studied to investigate the effects of nanofluid parameters on momentum, heat and mass transfers using the Buongiorno model. The experimental correlations for the properties of nanofluids are incorporated in the governing equations. A similarity analysis is performed to generate a set of ordinary differential equations describing the momentum, energy and mass transfers in the flow. These equations are solved numerically using the Runge–Kutta–Fehlberg method, which produces a fifth-order accurate solution. The numerical results are compared with the exact solutions for the regular fluids in the absence of nanofluid parameters and are found to be in good agreement. The results for the dimensionless velocity, temperature, wall shear stress, Nusselt and Sherwood numbers are presented graphically and compared for water-based nanofluids with ethylene-glycol-based nanofluids.

Sherwood number

Dimensionless quantity

Similarity solution

Momentum (technical analysis)

10.1177/1740349912456786

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Citations (4)

Large-Eddy Simulations and Heat-Flux Modeling in a Turbulent Impinging Jet

Numerical Heat Transfer Part A Applications (2009)

Naseem Uddin Sven Olaf Neumann Bernhard Weigand Bassam A. Younis

This article documents the results of an investigation into aspects of the simulation and modeling of turbulent jets that impinge orthogonally on a target surface. The focus is on the case of a jet which issues from a circular pipe into stagnant surrounding at the relatively high value of Reynolds number of 23,000 (based on nozzle diameter and bulk velocity) for which experimental data are available. Large-eddy simulations were performed to obtain details of the mean flows and the turbulence fields including distributions of all components of the turbulent heat fluxes. The outcome of these simulations were used to assess three alternative models for the turbulent heat fluxes which differ from the conventional Fourier's Law by not being based on the assumption of proportionality between the eddy and thermal diffusivities via a constant Prandtl number. It was found that only one of the models considered succeeds in representing the effects on the heat fluxes of the complex strain field associated with the stagnation region and the subsequent development into the wall-jet region. The reasons for this outcome are discussed.

Turbulent Prandtl number

Large-Eddy Simulation

10.1080/10407780902959324

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Citations (33)