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1
Content available Analysis of non-equidistant baffle spacing in a small shell and tube heat exchanger
Aziz Abdullah, Rehman Shafique
Archives of Thermodynamics
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2020
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Vol. 41, no 2
201--221
EN
Most of the formulations regarding the characteristics of a shell and tube heat exchanger have a common assumption; namely that the baffle plates are equidistant. This assumption fails to cater the real world scenario for defective baffles as the alteration in a shell and tube heat exchanger invalidates the equidistant baffle spacing of the plates. In this regard, a small six baffles heat exchanger was modeled in the computational fluid dynamics software package and studied by removing each baffle plate one at a time. Effect of removing each baffle plate on the temperature, pressure, heat transfer coefficient, and total heat transfer rate was recorded. It was observed that variation in the pressure drop for the same number of baffle plates varies along the axial order of the plates. The change in pressure drop due to the removal of the baffle plate near the inlet and the outlet was lowest and reaches a maximum in the axial center. It was also found that the plates below the radial center contribute higher towards the overall heat transfer as compared to those above.
2
Content available Beyond one-point turbulence closures
Wacławczyk M.
Transactions of the Institute of Fluid-Flow Machinery
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2017
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nr 135
29--40
EN
The paper concerns statistical description of turbulence in terms of multipoint velocity moments. A literature survey on possible multipoint turbulence closures and their future perspective is provided. We first consider the transport equations for two-point velocity statistics and their one-point limit. Another form of turbulence description, in terms of multipoint probability density functions is also introduced.
3
Content available On general-purpose turbulence models in CFD
Pozorski J.
Transactions of the Institute of Fluid-Flow Machinery
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2015
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nr 127
45--62
EN
The computational fluid dynamics (CFD) tools for various flow problems have become widespread nowadays, yet their use still needs attention and care. In particular, turbulence models are often a crucial part of flow computations undertaken with various software packages, either commercial, open-source or in-house. In the paper, an overview of available model categories is provided, together with some discussion of their advantages or drawbacks with respect to flow cases of interest.
4
Content available remote Three-zonal Wall Function for k-ε Turbulence Models
Chmielewski M., Gieras M.
Computational Methods in Science and Technology
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2013
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Vol. 19, No. 2
107--114
EN
Most commercially available wall functions for k-" turbulence models base on the two-zonal near-wall flow division assumption. Viscous and log-law sublayers are distinguished. In this article the three-zonal wall function concept with a buffer sublayer is developed. The aim of this new wall function is to improve the mean streamwise U+ velocity profile. The proposed wall function is validated on backward-facing step experimental data. Physical implications of the model performance are also discussed.
5
Content available remote Hybrid RANS/LES computation of plane impinging jet flow
Kubacki S., Rokicki J., Dick E.
Archives of Mechanics
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2011
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Vol. 63, nr 2
117-117
EN
Flow characteristics are presented of simulation results of plane impinging jets at high nozzle-plate distances, with two k-? based hybrid RANS/LES (Reynolds Averaged Navier–Stokes/Large–Eddy Simulation) models and a k-? RANS model. The first hybrid RANS/LES model is obtained by substitution of the turbulent length scale by the local grid size in the destruction term of the turbulent kinetic energy equation and in the definition of the eddy-viscosity. The second hybrid model is obtained by a latency factor in the definition of the eddy-viscosity. The RANS model overpredicts the length of the jet core region, caused by too weak turbulent mixing in the shear layers of the jet. This results in erroneous near-wall shear stress along the impingement plate. The hybrid RANS/LES models overcome the deficiency of the RANS model. Further, the hybrid models represent the flow with much more detail. For instance, the Görtler vortices are well reproduced in the stagnation flow region by the hybrid RANS/LES models.
6
Content available remote Performance of 3 Turbulence Models in 3D Flow Investigation for a 1.5-stage Turbine
Karczewski M., Błaszczak J.
TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk
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2008
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Vol. 12, No 3-4
185-195
EN
The object of this study was to investigate the flow phenomena in a cold air turbine built at the Institute of Jet Propulsion and Turbomachinery at Aachen Technical University (IST RWTH Aachen, Germany). The said turbine had been studied previously both experimentally and numerically on an IST’s flow solver called Panta Rhei. Since that time certain improvements, computational-wise, have been implemented in the code. In order to test them, new simulation runs were conducted. The detailed studies of the measured and computed flow angles as well as a flow velocity analysis are the means for this evaluation.
7
Content available remote Numeryczne badanie przepływu w 1.5 stopniowej turbinie z wykorzystaniem 3 modeli turbulencji
Karczewski M., Błaszczak J.
Zeszyty Naukowe. Cieplne Maszyny Przepływowe - Turbomachinery / Politechnika Łódzka
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2007
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nr 131
79-88
PL
Celem pracy było trójwymiarowe numeryczne zobrazowanie zjawisk przepływowych w 1.5-stopniowej turbinie modelowej Instytutu Napędów Odrzutowych i Maszyn Przepływowych w Nadreńsko-Westfalskiej Wyższej Szkole Technicznej (IST RWTH Aachen) w Akwizgranie (Niemcy). Do badań wykorzystano udoskonaloną wersję kodu obliczeniowego Panta Rhei, stworzonego przez niemiecki Instytut, a uzyskane wyniki obliczeń porównano z pomiarami eksperymentalnymi.
EN
The object of this study was an investigation of flow phenomena in a cold air turbine built at the Institute of Jet Propulsion and Turbomachinery at Aachen Technical University (IST RWTH Aachen, Germany). The said turbine was studied previously both experimentally and numerically with the IST's flow solver called Panta Rhei. Since that time certain improvements, computational-wise, were implemented in the code. In order to test them, new simulation runs were conducted.
8
Content available remote On some issues concerning the modeling of the motion of fluids
Rajagopal K. R., Tao L., Chen G. Q.
International Journal of Applied Mechanics and Engineering
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2005
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Vol. 10, no 3
475-487
EN
We address some issues regarding the use of the Lagrangian description and convected frames in describing fluid motions. We also discuss the implications of Brownian motion on modeling the macroscopic motion of fluids and the schemes of filtered simulations. The relevance of these issues to the modeling of turbulence is discussed in detail.
9
Content available remote Parametric study of two-phase flow in cyclonic separators for gas industry with application to gas turbines
Sierra F. Z., Garcia J. C., Juarez D., Kubiak J., Nicolas R.
Transactions of the Institute of Fluid-Flow Machinery
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2003
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nr 114
163-176
EN
In this work numerical analysis is used to carry out a parametric study of two-phase flow water-gasoil in a compact cyclonic separator (CCS). The study is oriented to produce a set of range parameters that may be used as a guide to control and manage multiphase mixtures separation with application to the gas industry, especially gas turbines. The cylindrical geometry under study has an aspect ratio of R=2.5 (where R=height/diameter). The CCS has two exits: one on the top for light liquid flow and one tangentially located in the bottom for heavy liquid flow. A finite volume approach has been employed with body-fitted coordinates in a 3-D solution of the liquid-liquid cyclonic flow. The turbulence was resolved using a RNG model, while the interactions between each component of the flow were addressed using a slip mixture model. The mixture under study is immiscible, and limited to the composition between 0.3 and 0.7 for water and consequently, from 0.7 to 0.3 for gasoil. The results indicate that the separation is sensitive to exist pressures, viscisity of light component gasoil and bubble size of the gasoil.
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