scholarly journals Evaluation of potential flow models for unsteady separated flow with respect to experimental data

2019 ◽  
Vol 4 (3) ◽  
Author(s):  
Field Manar ◽  
Anya R. Jones
Keyword(s):  
Experimental Data ◽  
Potential Flow ◽  
Separated Flow ◽  
Flow Models ◽  
Unsteady Separated Flow

A Review of Prediction Methods for Two-Phase Pressure Loss in Mini/Micro-Channels

2016 ◽  
Vol 24 (01) ◽  
pp. 1630002 ◽  
Author(s):  
Jung Hoon Yun ◽  
Ji Hwan Jeong
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Pressure Loss ◽  
Separated Flow ◽  
Empirical Correlations ◽  
Two Phase ◽  
Flow Models ◽  
Micro Channels ◽  
Extensive Experimental Data ◽  
Phase Pressure

Previous methods and correlations for predicting two-phase frictional pressure loss in mini/micro-channels are reviewed and compared. The empirical correlations are classified into four groups of modeling approaches: Homogeneous equilibrium models (HEMs), separated flow models (SFMs), direct empirical correlations, and flow pattern specific correlations. In order to examine the characteristics of the predictive methods for two-phase pressure loss in mini-channels and to assess the accuracy of the previous models and correlations, extensive experimental data and correlations that are available in the open literature are collected. The 1175 and 1304 experimental data for the two-phase pressure drop for condensing and boiling flows, respectively, are gathered from 15 papers and reports. The results present that the size of the channel significantly influences the pressure drop. The comparison demonstrates that Cicchitti et al.’s two-phase viscosity model is recommended for predicting two-phase pressure loss when the HEM is used. In general, the SFM with the two-phase multipliers of Muller–Steinhagen and Heck and Kim and Mudawar outperforms others for channel diameters of less than 3[Formula: see text]mm.

Base pressure prediction in bluff-body potential-flow models

2000 ◽  
Vol 423 ◽  
pp. 381-394 ◽  
Author(s):  
W. W. H. YEUNG ◽  
G. V. PARKINSON
Keyword(s):  
Potential Flow ◽  
Bluff Body ◽  
Separated Flow ◽  
Momentum Equation ◽  
Base Pressure ◽  
Vertex Angle ◽  
Arbitrary Vertex ◽  
Flow Models ◽  
Pressure Drag ◽  
Body Potential

In a recent study by Yeung & Parkinson (1997), a wake width was proposed which allowed the bluff-body potential-flow model by Parkinson & Jandali (1970) to be extended to include the flow around an oblique flat plate. By incorporating this wake width in the momentum equation originally derived by Eppler (1954) for separated flow, the drag of the plate is related to its inclination and base pressure through a simple analytical condition. It allows the base pressure, which is usually treated as an empirical input, to be determined theoretically and thus the model becomes self-contained. Predictions of the base pressure, drag and width of wake are found to be in reasonable agreement with the experimental data. When applied to the symmetrical flow around a wedge of arbitrary vertex angle, similar agreement with experimental measurements is obtained as well. It is also demonstrated that this condition is compatible with the free-streamline models by Wu (1962) and Wu & Wang (1964) such that the corresponding predictions are in good agreement with experiment.

Computation of Unsteady Separated Flow Fields Using Anisotropic Vorticity Elements

1996 ◽  
Vol 118 (4) ◽  
pp. 839-849 ◽  
Author(s):  
S. A. Huyer ◽  
J. R. Grant
Keyword(s):  
Experimental Data ◽  
Velocity Field ◽  
Separated Flow ◽  
Flow Fields ◽  
Single Element ◽  
Force Coefficient ◽  
Pitching Airfoil ◽  
Advection Term ◽  
Vorticity Production ◽  
Unsteady Separated Flow

A novel computational methodology to compute two-dimensional unsteady separated flow fields using a vorticity based formulation is presented. Unlike traditional vortex methods, the elements used in this method are designed to take advantage of the natural anisotropy of most external flows. These vortex elements are disjoint and of compact support. The vorticity is uniform over rectangular elements whose initial thickness is set by a diffusion length scale. The elements are a mathematical construction which enables the vorticity of the flow to be created and followed numerically, and the Biot-Savart integral to be performed. This integral specifies the associated velocity field. Since the vorticity of a single element is of finite extent, the velocity associated with an element is given by a nonsingular expression. Viscous diffusion effects are modeled using random walk and the advection term is computed by transporting the vorticity elements with the local velocity field. Consequently, this Lagrangian mesh continually evolves through time. Since pressure does not explicitly appear in the formulation, surface pressures are computed using a stagnation enthalpy formulation. These elements are used to compute vorticity production, accumulation, transport and viscous diffusion mechanisms for unsteady separated flow fields past a pitching airfoil. Dynamic stall vortex initiation and development were examined and compared with existing experimental data. Surface pressure data and integrated force coefficient data were found to be in excellent agreement with experimental data. Effects of geometry were provided with baseline calculations of the unsteady flow past an impulsively started cylinder. Both qualitative and quantitative comparisons with experimental data for equivalent test conditions establish the applicability of this approach to depict unsteady separated flow fields.

Aerodynamic characteristics of an unsteady separated flow

1979 ◽  
Author(s):  
M. FRANCIS ◽  
J. KEESEE ◽  
J. LANG ◽  
G. SPARKS ◽  
G. SISSON
Keyword(s):  
Separated Flow ◽  
Aerodynamic Characteristics ◽  
Unsteady Separated Flow

scholarly journals Identification of coexisting dynamics in boundary layer flows through proper orthogonal decomposition with weighting matrices

Meccanica ◽  
2021 ◽  
Author(s):  
Matteo Dellacasagrande ◽  
Dario Barsi ◽  
Patrizia Bagnerini ◽  
Davide Lengani ◽  
Daniele Simoni
Keyword(s):  
Experimental Data ◽  
Proper Orthogonal Decomposition ◽  
Fourier Transforms ◽  
Free Stream ◽  
Numerical Test ◽  
Separated Flow ◽  
Orthogonal Decomposition ◽  
Inner Product ◽  
Test Case ◽  
Proper Orthogonal

AbstractA different version of the classic proper orthogonal decomposition (POD) procedure introducing spatial and temporal weighting matrices is proposed. Furthermore, a newly defined non-Euclidean (NE) inner product that retain similarities with the POD is introduced in the paper. The aim is to emphasize fluctuation events localized in spatio-temporal regions with low kinetic energy magnitude, which are not highlighted by the classic POD. The different variants proposed in this work are applied to numerical and experimental data, highlighting analogies and differences with respect to the classic and other normalized variants of POD available in the literature. The numerical test case provides a noise-free environment of the strongly organized vortex shedding behind a cylinder. Conversely, experimental data describing transitional boundary layers are used to test the capability of the procedures in strongly not uniform flows. By-pass and separated flow transition processes developing with high free-stream disturbances have been considered. In both cases streaky structures are expected to interact with other vortical structures (i.e. free-stream vortices in the by-pass case and Kelvin–Helmholtz rolls in the separated type) that carry a significant different amount of energy. Modes obtained by the non-Euclidean POD (NE-POD) procedure (where weighted projections are considered) are shown to better extract low energy events sparse in time and space with respect to modes extracted by other variants. Moreover, NE-POD modes are further decomposed as a combination of Fourier transforms of the related temporal coefficients and the normalized data ensemble to isolate the frequency content of each mode.

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