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INTERFACE CONDITIONS FOR HYBRID RANS/LES CALCULATIONS
"... Hybrid RANS/LES methods, in which the attached boundary layers are simulated by RANS while the nonequilibrium regions of the flow are computed by LES, have received considerable attention over recent years. One issue that may affect (sometimes significantly) the accuracy of the results in hybrid me ..."
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Hybrid RANS/LES methods, in which the attached boundary layers are simulated by RANS while the nonequilibrium regions of the flow are computed by LES, have received considerable attention over recent years. One issue that may affect (sometimes significantly) the accuracy of the results in hybrid methods is the generation of turbulent eddies capable of supporting the Reynolds stresses in the LES region from a smooth RANS field (in which the Reynolds stress is due entirely to the model). We present results obtained in spatially developing turbulent channel flow in which synthetic turbulence is coupled with a controlled forcing technique that generates physically realistic turbulent eddies. This technique substantially reduces the distance required for the development of realistic turbulence. We discuss the effect of the free parameters used in this technique, and their optimization. Simulations are also performed that evaluate the effect of the approximations required when the full Reynoldsstress tensor is not know, and only statistics typically available from RANS simulations (the mean velocity and the Reynolds shear stress) are available. The effect of the quality of the synthetic turbulence at the inflow plane and the overall computational cost is also discussed. Finally, results from a simulation of an accelerating boundary layer are given.
Prediction of Separated Flow Characteristics over a Hump using RANS and DES
"... Predictions of the flow over a wallmounted hump are obtained using solutions of the Reynoldsaveraged NavierStokes (RANS) equations and DetachedEddy Simulation (DES). The upstream solution is characterized by a twodimensional turbulent boundary layer with a thickness approximately half of the ma ..."
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Predictions of the flow over a wallmounted hump are obtained using solutions of the Reynoldsaveraged NavierStokes (RANS) equations and DetachedEddy Simulation (DES). The upstream solution is characterized by a twodimensional turbulent boundary layer with a thickness approximately half of the maximum hump thickness measured at a location about two chord lengths upstream of the leading edge. The Reynolds number based on the hump chord length is 9.75 × 10 5. A slot at approximately 65 % chord (C) is used for flow control via a spatially uniform (with respect to the spanwise coordinate) steady suction, and with alternating suction/blowing. Solutions of the two and threedimensional RANS equations are obtained using the SpalartAllmaras and SST turbulence models. DES is applied to a threedimensional geometry corresponding to an extruded section of the hump. DES predictions of the baseline case exhibit a threedimensional chaotic structure in the wake, with a mean reverseflow region that is 20% shorter than predicted by the twodimensional RANS computations. DES predictions of the pressure coefficient in the separatedflow region for the baseline case exhibit good agreement with measurements and are more accurate than either the SA or SST RANS
A dynamic stochastic forcing method as a walllayer model for largeeddy simulation
 JOURNAL OF TURBULENCE
, 2006
"... ..."
DetachedEddy Simulation of a CoFlow Jet Airfoil at High Angle of Attack.” AIAA Paper 20094015
 Journal of Aircraft
, 2011
"... A detachededdy simulation (DES) of a co°ow jet (CFJ) airfoil at high angles of attack (AoA) is conducted in this paper. A low di®usion ECUSP (LDE) scheme with an implicit ¯fthorder WENO scheme is employed. DES appears to handle the turbulence mixing and °ow separation signi¯cantly better at high ..."
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A detachededdy simulation (DES) of a co°ow jet (CFJ) airfoil at high angles of attack (AoA) is conducted in this paper. A low di®usion ECUSP (LDE) scheme with an implicit ¯fthorder WENO scheme is employed. DES appears to handle the turbulence mixing and °ow separation signi¯cantly better at high AoA than RANS. 1
ii ACKNOWLEDGEMENTS
, 2009
"... I would firstly like to thank my friends and family for all their guidance and unwavering support throughout my PhD studies. Without their encouragement and good humour I doubt I would have kept my sunny disposition along the way. Furthermore I would like to truly acknowledge the support and guidanc ..."
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I would firstly like to thank my friends and family for all their guidance and unwavering support throughout my PhD studies. Without their encouragement and good humour I doubt I would have kept my sunny disposition along the way. Furthermore I would like to truly acknowledge the support and guidance of my supervisor, Professor Arne Holdø. Throughout my PhD he has been a source of wisdom and a friend. I would also like to thank my fellow students, as both friends and technical sound boards you have been invaluable in helping me get my thoughts on paper.
1 OPTIMIZING THE HYDROCYCLONE FOR BALLAST WATER TREATMENT USING COMPUTATIONAL FLUID DYNAMICS
"... Environmental concern related to the transfer of Invasive Aquatic Species by ships ballast water has given rise to the development of a vast array of ballast water treatment systems. The complex environmental challenges and tight operational characteristics of marine vessels limits the scope of tech ..."
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Environmental concern related to the transfer of Invasive Aquatic Species by ships ballast water has given rise to the development of a vast array of ballast water treatment systems. The complex environmental challenges and tight operational characteristics of marine vessels limits the scope of technologies used for Ballast Water Treatment. As a result few technologies have progressed beyond the Research and Development stage; however one of the most promising technologies for ship board use is the Cyclonic Separator, or Hydrocyclone. Despite the use of hydrocyclones in a wide variety of engineering applications they have yet to be successfully adapted towards the removal of suspended sediment and marine organisms from large volumes of ballast water. This paper details the operational characteristics of Ballast Water Hydrocyclones, employing empirical and experimental data to validate the use of a Detached Eddy Simulation (DES) turbulence model with
H&TECH
"... The flow around a cylinder at high Reynolds numbers is turbulence that can be compressed. Turbulence is an extraordinarily complex threedimensional flow, which is unsteady, erratic and composed of eddies. The characteristic of turbulence is the fluctuation of physical quantity generated by a rando ..."
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The flow around a cylinder at high Reynolds numbers is turbulence that can be compressed. Turbulence is an extraordinarily complex threedimensional flow, which is unsteady, erratic and composed of eddies. The characteristic of turbulence is the fluctuation of physical quantity generated by a random motion of vortex at different scales [8] performed the DES of flow around a cylinder in a uniform crossflow in the subcritical(laminarseparation) and postcritical(turbulentseparation) flow regimes. The results were very similar to those of the experiment and also with LES, especially at a subcritical Reynolds number of 5.0 × 10 4 . Gu et al. [10] used the DES method based on the SST twoequation turbulence model to stimulate the incompressible viscous flow around a cylinder. They proved that the DES method is valid and reliable to simulate the flow around a cylinder with a low or higher subcritical Reynolds number. Xu et al. ABSTRACT The combined section structure has been extensively used in engineering practice. However, there has been little research on the flow around a combined structure. Based on this situation, the numerical simulations of the flow around a combined pier with Reynolds numbers in the range of 1.0×10 6~2 .76×10 6 are performed. The time histories of lift coefficient and drag coefficient of three combined piers with different types (such as combined cylindrical pier, truncatedcone pier, combined truncatedcone pier) in different water depths are analyzed based on detached eddy simulation (DES) by using the fluid dynamics software FLUENT. The results show that the lift coefficient and drag coefficient between the combined cylindrical pier and the truncatedcone pier are basically the same under the condition of the same water depth. When the water depth is 3.0m, the drag coefficient of the combined truncatedcone pier is smaller than that of the combined cylindrical pier and truncatedcone pier. When the water depth is 4.0m or 5.0m, the drag coefficient of the combined truncatedcone pier is greater than that of the combined cylindrical pier and the truncatedcone pier. The form of the cross section of the submerged portion of the combined pier has a significant influence on the average drag coefficient under the condition of a different water depth.
1 KineticEddy Simulation of Static and Dynamic Stall
"... A KineticEddy Simulation (KES) approach has been developed for largeeddy simulation (LES) of wallbounded turbulent flow at high Reynolds numbers. The model solves for the local unresolved kinetic energy and the local subgrid length scale. The dissipation of the kinetic energy depends on the lengt ..."
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A KineticEddy Simulation (KES) approach has been developed for largeeddy simulation (LES) of wallbounded turbulent flow at high Reynolds numbers. The model solves for the local unresolved kinetic energy and the local subgrid length scale. The dissipation of the kinetic energy depends on the length scale, as well as on the length scale gradient. In most of flow domain of simulated cases, the subgrid length scale is of the order of the computational grid scale, and the KES approach behaves like a LES. In some other regions the length scale tends toward the integral scale and thus, smoothly approaches the very largeeddy simulation (VLES) limit. A robust KES approach is demonstrated here that employs the realizability constraints to bound the model parameters. The realizable KES has been applied to static stall around a 3D NACA0015 wing, oscillatory attached and dynamic light stall, and dynamic deep stall flows around a 2D NACA0015 airfoil. Vortex shedding and massive separation of the boundary layer at high Reynolds number are clearly captured. The behavior of the realizable KES approach on high angleofattack aerodynamics is studied.
TURBULENCE MODELING ISSUES IN ADS THERMAL AND HYDRAULIC ANALYSES
"... Accelerator Driven nuclear reactor Systems (ADS) have in several respects a prototypical character of the flow and cooling conditions combined with narrow operating conditions due to the materials engaged. E.g. the high local thermal load in the liquid metal cooled spallation target requires a very ..."
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Accelerator Driven nuclear reactor Systems (ADS) have in several respects a prototypical character of the flow and cooling conditions combined with narrow operating conditions due to the materials engaged. E.g. the high local thermal load in the liquid metal cooled spallation target requires a very careful analysis by experimental and numerical means. Some of the main goals of the numerical analyses of the thermal dynamics of those systems and of required experiments are discussed. The prediction of locally detached and recirculating flows suffers from insufficient turbulence modeling; this has to be compensated by using prototypical model experiments, e.g. with water, to select the adequate models and numerical schemes. Some sensitivities and model uncertainties are discussed; some of them are reduced by socalled layered models like in the SST turbulence model or the DES. The well known problems with the Reynolds analogy in predicting the heat transfer in liquid metals requires prototypic liquid metal experiments to select and adapt the turbulent heat flux models. The uncertainties in liquid metal experiments cannot be neglected; so it is necessary to perform CFD calculations and experiments always hand in hand and to develop improved turbulent heat flux models. One contribution to an improved 3 or 4equation model is deduced from recent Direct Numerical Simulation data. Of course, the ADS community would need such extended heat flux models, but even realizing standard 3 or 4equation ASM heat flux models in the commercial CFD codes would allow for an improved heat transfer modeling, especially when buoyancy is involved.