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Frederick Stern - One of the best experts on this subject based on the ideXlab platform.
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Unsteady free surface wave-Induced Separation : Vortical structures and instabilities
Journal of Fluids and Structures, 2009Co-Authors: Manivannan Kandasamy, Tao Xing, Frederick SternAbstract:Abstract Vortical structures and instability mechanisms of the unsteady free surface wave-Induced Separation around a surface-piercing NACA0024 foil at a Froude number of 0.37 and a Reynolds number of 1.52×106 are studied using an unsteady Reynolds-averaged Navier–Stokes (URANS) code with a blended k−e/k−ω turbulence model and a free surface tracking method. At the free surface, the separated flow reattaches to the foil surface resulting in a wall-bounded Separation bubble. The mean and instantaneous flow topologies in the Separation region are similar to the owl-face pattern. The initial shear-layer instability, the Karman-like instability, and the flapping instability are identified, and their scaling and physical mechanisms are studied. Validation with experimental fluid dynamics (EFD) and comparison with complementary detached-eddy simulation (DES) indicate that URANS resolves part of the organized oscillations due to the large-scale unsteady vortical structures and instabilities, thereby capturing the gross features of the unsteady Separation. The URANS solutions show an initial amplitude defect of 30% for the free surface oscillations where the shear layer separates, and the defect progressively increases downstream as URANS rapidly dissipates the rolled up vortices.
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Unsteady free-surface wave-Induced Separation: analysis of turbulent structures using detached eddy simulation and single-phase level set
Journal of Turbulence, 2007Co-Authors: Tao Xing, Mani Kandasamy, Frederick SternAbstract:Turbulent structures of the unsteady free-surface wave-Induced Separation around a surface-piercing NACA0024 are studied using a detached-eddy simulation with a single-phase level set method. Quantitative verification and validation show good agreement with experimental data. Instantaneous and mean flows show an owl-type Separation with the same instability frequencies identified by unsteady Reynolds-averaged Navier–Stokes. Anisotropy invariant maps show that turbulence is anisotropic in the middle of the Separation region and is at a two-component state near the foil surface. The turbulent kinetic energy and its budget have similarities to that of a separated turbulent boundary layer near the toe and a backward-facing step flow in the recirculation region, but with large three-dimensional and free-surface effects. The free-surface damps velocity and pressure fluctuations and moves the peaks of turbulence quantities from the high-speed to the low-speed side of the free shear layer.
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DES and RANS of Unsteady Free- Surface Wave Induced Separation
42nd AIAA Aerospace Sciences Meeting and Exhibit, 2004Co-Authors: Tao Xing, Mani Kandasamy, Robert Wilson, Frederick SternAbstract:vortex and turbulence interactions. First identified and studied using a surface-piercing foil mounted on the floor of a hydraulic flume. This building block geometry facilitates identification of the salient features; since, the foil profile was designed for limited Separation for the deep, no-wave, and twodimensional (2D) condition. Tests were conducted for Froude number ( gc Uc / = Fr ) range 0. 20.48 with average Reynolds number ( ν / Re c U c = ) = 7x10 (where Uc=carriage speed, c=chord length, and ν=kinematic viscosity). Wave profile photographs and needlepoint, dye injection flow visualization was used to determine the length and depth of the Separation region. Separation was defined by a region of highly disturbed free-surface flow, which initiated just beyond the wave trough and extended to the foil trailing edge for all but the highest Fr ranging from Separation starting point x/c=. 7 at small Fr=. 2, to maximum x/c=. 42 at medium Fr=. 25, and x/c=. 6 at Fr=. 37. Beyond the Separation starting point, the wave profile was nearly constant. The depth of Separation was defined by reversed axial flow and upward cross flow, which was observed close to the foil surface in a wedge shaped region gradually expanding from the Separation starting point to a maximum depth near the foil trailing edge with magnitude similar to the wave height. Stratford’s laminar Separation criterion showed good agreement with Separation starting point data. A general-purpose unsteady Reynolds-averaged Navier-Stokes (URANS) research code CFDSHIPIOWA developed for ship hydrodynamics application is extended for detached eddy simulation (DES) capability. CFDSHIP-IOWA uses surface-tracking free-surface model, k-ω turbulence model, and high performance computing. Both 2 and 3 order upwind biased scheme for spatial derivatives were applied for URANS while 3 order upwind biased scheme used for DES. DES extensions are based on the blended k-ω model by modifying the length scale in the k equation and validated with surface piercing NACA 0024 benchmark, including IIHR towing-tank EFD data and concurrent URANS. Domain and grid convergence studies were conducted for 2 order RANS. 3 order RANS was also studied on a coarse grid and a 3 order DES was conducted on both coarse and medium grids. Statistical analysis of the results, including time history, running mean, and FFT of total drag and side forces, mean and RMS of wave elevations and pressure on foil surface, and unsteady 3D Separation flow pattern are presented. Results show fairly good agreement EFD validation data for mean, RMS, and FFT frequencies for wave elevations and surface pressure; however, many modeling and numerical issues remain. Seemingly credible flow features of unsteady wave-Induced Separation have been simulated for the first time, which will be used to guide future PIV measurements. More recently, [2-4] used a similar geometry (surface-piercing NACA 0024) for complementary towing-tank (3x3x100m) experimental fluid dynamics (EFD) and steady RANS computational fluid dynamics (CFD). Wave profiles, mean far field wave elevations, and mean and RMS near field wave elevations and surface-pressure measurements were made for c=1.2m and deep draft d=1.5m foil and Fr=0.19, 0.37, and 0.55 and Re=(0.822, 1.52, 2.26) x 10. EFD results similar to[1], except differences foil geometry and restricted water and foil bottom effects. Steady RANS solutions show good agreement wave profiles and surface pressure, but only fair agreement wave elevations due to poor resolution short waves for low Fr and Separation region for medium Fr. RANS solutions also provide details of separated flow pattern, but data not yet available for validation
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Free-Surface Wave-Induced Separation
Journal of Fluids Engineering, 1996Co-Authors: Z. J. Zhang, Frederick SternAbstract:Free-surface wave-Induced Separation is studied for a surface-piercing NACA 0024 foil over a range of Froude numbers (0, .2, .37, .55) through computational fluid dynamics of the unsteady Reynolds-averaged Navier-Stokes and the continuity equations with the Baldwin-Lomax turbulence model, exact nonlinear kinematic and approximate dynamic free-surface boundary conditions, and a body/free-surface conforming grid. The flow conditions and uncertainty analysis are discussed. A topological rule for a surface-piercing body is derived and verified. Steady-flow results are presented and analyzed with regard to the wave and viscous flow and the nature of the Separation.
Remko M. Boom - One of the best experts on this subject based on the ideXlab platform.
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Quality of shear fractionated wheat gluten – comparison to commercial vital wheat gluten
Journal of Cereal Science, 2011Co-Authors: Elizabeth E. J. Van Der Zalm, Atze Jan Van Der Goot, Remko M. BoomAbstract:Abstract The functional properties of gluten obtained with a shear-Induced Separation process, recently proposed by Peighambardoust et al. (2008) , are compared with a commercially available vital wheat gluten. Two tests were performed. First, a relatively strong wheat flour, Soissons, was enriched with gluten protein. The resulting dough was then evaluated on its kneading performance. Second, a weak flour, Kolibri, was enriched to evaluate the baking properties. The wheat flour enriched with gluten protein obtained via the shear-Induced Separation process (SCG) showed comparable to improved gluten functionality relative to commercial available vital wheat gluten protein (CVWG). The differences in functionality cannot be directly related to the composition as analyzed with SE-HPLC, because the composition of the gluten materials was rather comparable. The differences in functionality may therefore be related to the different drying techniques used or to the inherent mildness of the shear-Induced Separation technique.
Tao Xing - One of the best experts on this subject based on the ideXlab platform.
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Unsteady free surface wave-Induced Separation : Vortical structures and instabilities
Journal of Fluids and Structures, 2009Co-Authors: Manivannan Kandasamy, Tao Xing, Frederick SternAbstract:Abstract Vortical structures and instability mechanisms of the unsteady free surface wave-Induced Separation around a surface-piercing NACA0024 foil at a Froude number of 0.37 and a Reynolds number of 1.52×106 are studied using an unsteady Reynolds-averaged Navier–Stokes (URANS) code with a blended k−e/k−ω turbulence model and a free surface tracking method. At the free surface, the separated flow reattaches to the foil surface resulting in a wall-bounded Separation bubble. The mean and instantaneous flow topologies in the Separation region are similar to the owl-face pattern. The initial shear-layer instability, the Karman-like instability, and the flapping instability are identified, and their scaling and physical mechanisms are studied. Validation with experimental fluid dynamics (EFD) and comparison with complementary detached-eddy simulation (DES) indicate that URANS resolves part of the organized oscillations due to the large-scale unsteady vortical structures and instabilities, thereby capturing the gross features of the unsteady Separation. The URANS solutions show an initial amplitude defect of 30% for the free surface oscillations where the shear layer separates, and the defect progressively increases downstream as URANS rapidly dissipates the rolled up vortices.
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Unsteady free-surface wave-Induced Separation: analysis of turbulent structures using detached eddy simulation and single-phase level set
Journal of Turbulence, 2007Co-Authors: Tao Xing, Mani Kandasamy, Frederick SternAbstract:Turbulent structures of the unsteady free-surface wave-Induced Separation around a surface-piercing NACA0024 are studied using a detached-eddy simulation with a single-phase level set method. Quantitative verification and validation show good agreement with experimental data. Instantaneous and mean flows show an owl-type Separation with the same instability frequencies identified by unsteady Reynolds-averaged Navier–Stokes. Anisotropy invariant maps show that turbulence is anisotropic in the middle of the Separation region and is at a two-component state near the foil surface. The turbulent kinetic energy and its budget have similarities to that of a separated turbulent boundary layer near the toe and a backward-facing step flow in the recirculation region, but with large three-dimensional and free-surface effects. The free-surface damps velocity and pressure fluctuations and moves the peaks of turbulence quantities from the high-speed to the low-speed side of the free shear layer.
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DES and RANS of Unsteady Free- Surface Wave Induced Separation
42nd AIAA Aerospace Sciences Meeting and Exhibit, 2004Co-Authors: Tao Xing, Mani Kandasamy, Robert Wilson, Frederick SternAbstract:vortex and turbulence interactions. First identified and studied using a surface-piercing foil mounted on the floor of a hydraulic flume. This building block geometry facilitates identification of the salient features; since, the foil profile was designed for limited Separation for the deep, no-wave, and twodimensional (2D) condition. Tests were conducted for Froude number ( gc Uc / = Fr ) range 0. 20.48 with average Reynolds number ( ν / Re c U c = ) = 7x10 (where Uc=carriage speed, c=chord length, and ν=kinematic viscosity). Wave profile photographs and needlepoint, dye injection flow visualization was used to determine the length and depth of the Separation region. Separation was defined by a region of highly disturbed free-surface flow, which initiated just beyond the wave trough and extended to the foil trailing edge for all but the highest Fr ranging from Separation starting point x/c=. 7 at small Fr=. 2, to maximum x/c=. 42 at medium Fr=. 25, and x/c=. 6 at Fr=. 37. Beyond the Separation starting point, the wave profile was nearly constant. The depth of Separation was defined by reversed axial flow and upward cross flow, which was observed close to the foil surface in a wedge shaped region gradually expanding from the Separation starting point to a maximum depth near the foil trailing edge with magnitude similar to the wave height. Stratford’s laminar Separation criterion showed good agreement with Separation starting point data. A general-purpose unsteady Reynolds-averaged Navier-Stokes (URANS) research code CFDSHIPIOWA developed for ship hydrodynamics application is extended for detached eddy simulation (DES) capability. CFDSHIP-IOWA uses surface-tracking free-surface model, k-ω turbulence model, and high performance computing. Both 2 and 3 order upwind biased scheme for spatial derivatives were applied for URANS while 3 order upwind biased scheme used for DES. DES extensions are based on the blended k-ω model by modifying the length scale in the k equation and validated with surface piercing NACA 0024 benchmark, including IIHR towing-tank EFD data and concurrent URANS. Domain and grid convergence studies were conducted for 2 order RANS. 3 order RANS was also studied on a coarse grid and a 3 order DES was conducted on both coarse and medium grids. Statistical analysis of the results, including time history, running mean, and FFT of total drag and side forces, mean and RMS of wave elevations and pressure on foil surface, and unsteady 3D Separation flow pattern are presented. Results show fairly good agreement EFD validation data for mean, RMS, and FFT frequencies for wave elevations and surface pressure; however, many modeling and numerical issues remain. Seemingly credible flow features of unsteady wave-Induced Separation have been simulated for the first time, which will be used to guide future PIV measurements. More recently, [2-4] used a similar geometry (surface-piercing NACA 0024) for complementary towing-tank (3x3x100m) experimental fluid dynamics (EFD) and steady RANS computational fluid dynamics (CFD). Wave profiles, mean far field wave elevations, and mean and RMS near field wave elevations and surface-pressure measurements were made for c=1.2m and deep draft d=1.5m foil and Fr=0.19, 0.37, and 0.55 and Re=(0.822, 1.52, 2.26) x 10. EFD results similar to[1], except differences foil geometry and restricted water and foil bottom effects. Steady RANS solutions show good agreement wave profiles and surface pressure, but only fair agreement wave elevations due to poor resolution short waves for low Fr and Separation region for medium Fr. RANS solutions also provide details of separated flow pattern, but data not yet available for validation
Mahmoud M. El-halwagi - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of Heat-Induced Separation Networks for Condensation of Volatile Organic Compounds
Sustainable Design Through Process Integration, 2017Co-Authors: Mahmoud M. El-halwagiAbstract:Mass-exchange operations employ mass-separating agents to induce the transfer of targeted components from the rich phase to the lean phase. Another important class of Separations involves the use of energy-separating agents to induce Separations. This chapter deals with the optimal design of heat-Induced Separation networks (HISENs). Examples of HISENs include condensation, crystallization, and drying. The chapter will focus on condensation because of its importance in recovering volatile organic compounds (VOCs), which are among the most serious atmospheric pollutants. A shortcut graphical method will be presented. This method is primarily based on the work of Richburg and El-Halwagi (1995). More generalized procedures and broader applications can be found in the literature.
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Pollution Prevention through Process Integration - Chapter 12 – Synthesis of Heat-Induced Separation Networks for Condensation of Volatile Organic Compounds
Sustainable Design Through Process Integration, 2012Co-Authors: Mahmoud M. El-halwagiAbstract:Publisher Summary This chapter deals with the optimal design of heat-Induced Separation networks (HISENs). This class of Separations involves the use of energy-separating agents to induce Separations. Examples of HISENs include condensation, crystallization, and drying. The VOC-condensation system involves three units. The initial step is to cool the stream to a temperature slightly above the freezing point of water, to dehumidify the gas to prevent detrimental icing effects in subsequent stages. Next, the stream is cooled to recover the VOC. The temperature is an optimization variable. To utilize the cooling capacity of the gaseous stream, it is recycled back to the system for heat integration. The remaining cooling duty is accomplished by a refrigerant. The primary objective of the VOC-condensation system is to meet mass-recovery objectives. But, since heat is a key element in realizing the mass objectives, the mass and heat interactions of the problem have to be identified and reconciled. This can be achieved by converting the VOC-recovery task from a mass-transfer to a heat-transfer duty, by relating the composition of the VOC to the temperature of the gaseous waste. The design procedure starts by identifying the minimum utility cost for a given heat-transfer driving force. Next, the fixed and operating costs are traded off by iterating over the driving forces until the minimum total annualized cost is attained. Once the minimum utility cost has been identified, trade-offs between operating and fixed costs must be established. Next, the minimum approach temperatures are altered, until the minimum total annualized cost is identified.
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Synthesis of optimal heat-Induced Separation networks
Chemical Engineering Science, 1995Co-Authors: Mahmoud M. El-halwagi, B.k. Srinivas, Russell F. DunnAbstract:Abstract In this work we introduce the novel problem of synthesizing heat-Induced Separation networks (HISENs). The essence of HISEN synthesis is to reduce the concentration of a certain component in a number of rich (typically waste) streams from a set of supply compositions to a set of target compositions by using a number of heat-Induced separators. A heat-Induced separator is any indirect contact unit which employs an energy-separating agent (ESA) to affect Separation via phase change. Examples of these systems include condensation, crystallization, vaporization and drying. By combining phase-equilibrium data with enthalpy balances, we develop pinch diagrams that can be used to determine the minimum operating cost of the system. There are two distinctive characteristics associated with the pinch diagrams for the HISENs. First, the location of the pinch point is not restricted to the supply temperatures of streams. Second, heat-Induced separators may straddle the pinch point even for networks featuring the minimum cost of energy-separating agents. A systematic procedure is presented to address these characteristics and to synthesize a cost effective network of heat-Induced separators. The problem is formulated as an optimization program. A solution procedure that is guaranteed to identify the global solution is devised to solve the problem. In addition, a slightly revised formulation is developed to incorporate the effect of stream bypass/mixing. Several case studies are tackled using the proposed procedures.
Manivannan Kandasamy - One of the best experts on this subject based on the ideXlab platform.
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Unsteady free surface wave-Induced Separation : Vortical structures and instabilities
Journal of Fluids and Structures, 2009Co-Authors: Manivannan Kandasamy, Tao Xing, Frederick SternAbstract:Abstract Vortical structures and instability mechanisms of the unsteady free surface wave-Induced Separation around a surface-piercing NACA0024 foil at a Froude number of 0.37 and a Reynolds number of 1.52×106 are studied using an unsteady Reynolds-averaged Navier–Stokes (URANS) code with a blended k−e/k−ω turbulence model and a free surface tracking method. At the free surface, the separated flow reattaches to the foil surface resulting in a wall-bounded Separation bubble. The mean and instantaneous flow topologies in the Separation region are similar to the owl-face pattern. The initial shear-layer instability, the Karman-like instability, and the flapping instability are identified, and their scaling and physical mechanisms are studied. Validation with experimental fluid dynamics (EFD) and comparison with complementary detached-eddy simulation (DES) indicate that URANS resolves part of the organized oscillations due to the large-scale unsteady vortical structures and instabilities, thereby capturing the gross features of the unsteady Separation. The URANS solutions show an initial amplitude defect of 30% for the free surface oscillations where the shear layer separates, and the defect progressively increases downstream as URANS rapidly dissipates the rolled up vortices.