Analysis of Performance of Cavitation Models with Analytically Calculated Coefficients

Cavitation is often simulated using a mixture model, which considers the transport of an active scalar, namely the vapor fraction αv. Source and sink terms of the transport equation of αv, namely vaporization and condensation terms, rule the dynamics of the cavity and are described through different models. These models contain empirical coefficients generally calibrated through optimization processes. The purpose of this paper is to propose an analytical approach for the calculation of the coefficients, based on the time scales of vaporization and condensation processes. Four different models are compared considering as a test-case a two-dimensional flow around a cylinder. Some relevant quantities are analyzed both for standard value of coefficients, as found in the literature, and the coefficients calculated through the analytical approach. The study shows that the analytical computation of the coefficients of the model substantially improve the results, and the models considered give similar results, both in terms of cavitation regime and mean vapor fraction produced.

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Numerical Investigation of Boundary Layers in Wet Steam Nozzles

Volume 8: Microturbines, Turbochargers and Small Turbomachines; Steam Turbines ◽

10.1115/gt2016-57598 ◽

2016 ◽

Cited By ~ 1

Author(s):

Jörg Starzmann ◽

Fiona R. Hughes ◽

Alexander J. White ◽

Marius Grübel ◽

Damian M. Vogt

Keyword(s):

Boundary Layer ◽

Boundary Layers ◽

Three Dimensional ◽

Side Wall ◽

Turbulence Models ◽

Test Case ◽

Wet Steam ◽

Compression Waves ◽

Wall Boundary Layer ◽

Two Dimensional Flow

Condensing nozzle flows have been used extensively to validate wet steam models. Many test cases are available in the literature and in the past a range of numerical studies have dealt with this challenging task. It is usually assumed that the nozzles provide a one- or two-dimensional flow with a fully turbulent boundary layer. The present paper reviews these assumptions and investigates numerically the influence of boundary layers on dry and wet steam nozzle expansions. For the narrow nozzle of Moses and Stein it is shown that the pressure distribution is significantly affected by the additional blockage due to the side wall boundary layer. Comparison of laminar and turbulent flow predictions for this nozzles suggests that laminar-turbulent transition only occurs after the throat. Other examples are the Binnie nozzle and the Moore nozzles for which it is known that sudden changes in wall curvature produce expansion and compression waves that interact with the boundary layers. The differences between two- and three-dimensional calculations for these cases and the influence of laminar and turbulent boundary layers are discussed. The present results reveal that boundary layer effects can have a considerable impact on the mean nozzle flow and thus on the validation process of condensation models. In order to verify the accuracy of turbulence modelling a test case that is not widely known internationally is included within the present study. This experimental work is remarkable because it includes boundary layer data as well as the usual pressure measurements along the nozzle centreline. Predicted and measured boundary layer profiles are compared and the effect of different turbulence models is discussed. Most of the numerical results are obtained with the in-house wet steam RANS-solver, Steamblock, but for the purpose of comparison the commercial program ANSYS CFX is also used, providing a wider range of standard RANS-based turbulence models.

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Performance of Two-Equation Turbulence Models for Flat Plate Flows With Leading Edge Bubbles

Journal of Fluids Engineering ◽

10.1115/1.2829596 ◽

2008 ◽

Vol 130 (2) ◽

Cited By ~ 9

Author(s):

S. Collie ◽

M. Gerritsen ◽

P. Jackson

Keyword(s):

Flat Plate ◽

Turbine Blades ◽

Turbulence Models ◽

Leading Edge ◽

Test Case ◽

Sst Model ◽

Two Dimensional Flow ◽

Experimental Values ◽

University Of Bristol ◽

Sharp Leading Edge

This paper investigates the performance of the popular k-ω and SST turbulence models for the two-dimensional flow past the flat plate at shallow angles of incidence. Particular interest is paid to the leading edge bubble that forms as the flow separates from the sharp leading edge. This type of leading edge bubble is most commonly found in flows past thin airfoils, such as turbine blades, membrane wings, and yacht sails. Validation is carried out through a comparison to wind tunnel results compiled by Crompton (2001, “The Thin Aerofoil Leading Edge Bubble,” Ph.D. thesis, University of Bristol). This flow problem presents a new and demanding test case for turbulence models. The models were found to capture the leading edge bubble well with the Shear-Stress Transport (SST) model predicting the reattachment length within 7% of the experimental values. Downstream of reattachment both models predicted a slower boundary layer recovery than the experimental results. Overall, despite their simplicity, these two-equation models do a surprisingly good job for this demanding test case.

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Immersive Computing Technology to Investigate Tradeoffs Under Uncertainty in Disassembly Sequence Planning

Journal of Mechanical Design ◽

10.1115/1.4025021 ◽

2014 ◽

Vol 136 (7) ◽

Cited By ~ 8

Author(s):

Sara Behdad ◽

Leif Berg ◽

Judy Vance ◽

Deborah Thurston

Keyword(s):

User Interfaces ◽

Analytical Approach ◽

Mathematical Optimization ◽

Cost Effective ◽

Test Case ◽

Computing Technology ◽

Disassembly Sequence Planning ◽

Sequence Planning ◽

Trade Offs ◽

Disassembly Sequence

The scientific and industrial communities have begun investigating the possibility of making product recovery economically viable. Disassembly sequence planning may be used to make end-of-life product take-back processes more cost effective. Much of the research involving disassembly sequence planning relies on mathematical optimization models. These models often require input data that is unavailable or can only be approximated with high uncertainty. In addition, there are few mathematical models that include consideration of the potential of product damage during disassembly operations. The emergence of Immersive Computing Technologies (ICT) enables designers to evaluate products without the need for physical prototypes. Utilizing unique 3D user interfaces, designers can investigate a multitude of potential disassembly operations without resorting to disassembly of actual products. The information obtained through immersive simulation can be used to determine the optimum disassembly sequence. The aim of this work is to apply a decision analytical approach in combination with immersive computing technology to optimize the disassembly sequence while considering trade-offs between two conflicting attributes: disassembly cost and damage estimation during disassembly operations. A wooden Burr puzzle is used as an example product test case. Immersive human computer interaction is used to determine input values for key variables in the mathematical model. The results demonstrate that the use of dynamic programming algorithms coupled with virtual disassembly simulation is an effective method for evaluating multiple attributes in disassembly sequence planning. This paper presents a decision analytical approach, combined with immersive computing techniques, to optimize the disassembly sequence. Future work will concentrate on creating better methods of estimating damage in virtual disassembly environments and using the immersive technology to further explore the feasible design space.

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The early stages of shallow flows in an inclined flume

Journal of Fluid Mechanics ◽

10.1017/s0022112009007034 ◽

2009 ◽

Vol 633 ◽

pp. 285-309 ◽

Cited By ~ 10

Author(s):

MATTEO ANTUONO ◽

ANDREW J. HOGG ◽

MAURIZIO BROCCHINI

Keyword(s):

Shallow Water ◽

Shallow Water Equations ◽

Numerical Algorithms ◽

Test Case ◽

Discontinuous Solutions ◽

Shallow Flows ◽

Moving Interface ◽

Nonlinear Shallow Water Equations ◽

Two Dimensional Flow ◽

Height Fields

The motion of an initially quiescent shallow layer of fluid within an impulsively tilted flume is modelled using the nonlinear shallow water equations. Analytical solutions for the two-dimensional flow are constructed using the method of characteristics and, in regions where neither of the characteristic variables is constant, by adopting hodograph variables and using the Riemann construction for the solution. These solutions reveal that the motion is strongly influenced by the impermeable endwalls of the flume. They show that discontinuous solutions emerge after some period following the initiation of the flow and that for sufficiently long flumes there is a moving interface between wetted and dry regions. Using the hodograph variables we are able to track the evolution of the flow analytically. After the discontinuities develop, we also calculate the velocity and height fields by using jump conditions to express conservation of mass and momentum across the shock and thus we show how the hydraulic jump moves within the domain and how its magnitude grows. In addition to providing the behaviour of the flow in this physical scenario, this unsteady solution also provides an important test case for numerical algorithms designed to integrate the shallow water equations.

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Passive separation control using a self-adaptive hairy coating

Journal of Fluid Mechanics ◽

10.1017/s0022112009006119 ◽

2009 ◽

Vol 627 ◽

pp. 451-483 ◽

Cited By ~ 60

Author(s):

JULIEN FAVIER ◽

ANTOINE DAUPTAIN ◽

DAVIDE BASSO ◽

ALESSANDRO BOTTARO

Keyword(s):

Circular Cylinder ◽

Stokes Equations ◽

Navier Stokes ◽

Separation Control ◽

Test Case ◽

Navier Stokes Equations ◽

Partitioned Approach ◽

Passive Separation ◽

Two Dimensional Flow ◽

Interaction Problem

A model of hairy medium is developed using a homogenized approach, and the fluid flow around a circular cylinder partially coated with hair is analysed by means of numerical simulations. The capability of this coating to adapt to the surrounding flow is investigated, and its benefits are discussed in the context of separation control. This fluid–structure interaction problem is solved with a partitioned approach, based on the direct resolution of the Navier–Stokes equations together with a nonlinear set of equations describing the dynamics of the coating. A volume force, arising from the presence of a cluster of hair, provides the link between the fluid and the structure problems. For the structure part, a subset of reference elements approximates the whole layer. The dynamics of these elements is governed by a set of equations based on the inertia, elasticity, interaction and losses effects of articulated rods. The configuration chosen is that of the two-dimensional flow past a circular cylinder at Re = 200, a simple and well-documented test case. Aerodynamics performances quantified by the Strouhal number, the drag and the maximum lift in the laminar unsteady regime are modified by the presence of the coating. A set of parameters corresponding to a realistic coating (length of elements, porosity, rigidity) is found, yielding an average drag reduction of 15% and a decrease of lift fluctuations by about 40%, associated to a stabilization of the wake.

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Continuous low-level aquatic monitoring (CLAM) samplers for pesticide contaminant screening in urban runoff: Analytical approach and a field test case

Chemosphere ◽

10.1016/j.chemosphere.2017.06.085 ◽

2017 ◽

Vol 184 ◽

pp. 1028-1035 ◽

Cited By ~ 3

Author(s):

Michael P. Ensminger ◽

Martice Vasquez ◽

Hsing-Ju Tsai ◽

Sarah Mohammed ◽

A. Van Scoy ◽

...

Keyword(s):

Field Test ◽

Analytical Approach ◽

Urban Runoff ◽

Test Case ◽

Low Level

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The Dynamics of TAT Process

Rorschachiana Journal of the International Society for the Rorschach ◽

10.1027/1192-5604/a000056 ◽

2014 ◽

Vol 35 (2) ◽

pp. 103-133 ◽

Cited By ~ 6

Author(s):

Benoît Verdon ◽

Catherine Chabert ◽

Catherine Azoulay ◽

Michèle Emmanuelli ◽

Françoise Neau ◽

...

Keyword(s):

Defense Mechanisms ◽

Analytical Approach ◽

Therapeutic Process ◽

Practice Research ◽

Rorschach Test ◽

Mental Functioning ◽

Projective Tests ◽

The Subject ◽

Latent Content ◽

Rigorous Method

After many years of clinical practice, research and the teaching of projective tests, Shentoub and her colleagues (Debray, Brelet, Chabert & al.) put forward an original and rigorous method of analysis and interpretation of the TAT protocols in terms of psychoanalysis and clinical psychopathology. They developed the TAT process theory in order to understand how the subject builds a narrative. Our article will emphasize the source of the analytical approach developed by V. Shentoub in the 1950s to current research; the necessity of marking the boundary between the manifest and latent content in the cards; the procedure for analyzing the narrative, supported by an analysis sheet for understanding the stories' structure and identifying the defense mechanisms; and how developing hypotheses about how the mental functions are organized, as well as their potential psychopathological characteristics; and the formulation of a diagnosis in psychodynamic terms. In conjunction with the analysis and interpretation of the Rorschach test, this approach allows us to develop an overview of the subject's mental functioning, taking into account both the psychopathological elements that may threaten the subject and the potential for a therapeutic process. We will illustrate this by comparing neurotic, borderline, and psychotic personalities.

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