Blockage Effects on Cavitation Inception Characteristics of Bluff Bodies

1991 ◽  
Vol 205 (6) ◽  
pp. 415-419 ◽  
Author(s):  
R Balachandar ◽  
A S Ramamurthy
Keyword(s):  
Bluff Body ◽  
Experimental Results ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Interference Effects ◽  
Cavitation Inception ◽  
Proposed Model

The study deals with the prediction of cavitation inception in the wake of two-dimensional bluff bodies subject to wall interference effects. Corrections are included in the model to account for flow entrainment effects and loss of circulation in the vortices shed from the bluff body. Experimental results are also presented to verify the proposed model over a range of blockages.

A Note on Choking Cavitation Flow Past Bluff Bodies

1992 ◽  
Vol 114 (3) ◽  
pp. 439-442 ◽  
Author(s):  
A. S. Ramamurthy ◽  
R. Balachandar
Keyword(s):  
Pressure Distribution ◽  
Cavitation Number ◽  
Experimental Results ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Interference Effects ◽  
Cavitation Flow ◽  
Prismatic Body ◽  
Flow Past

A model is developed to predict the choking cavitation number for sharp edged bluff bodies subject to wall interference effects. The fact that the forebody pressure distribution under cavitating conditions essentially resembles the values obtained in noncavitating flows is made use of in the development of the model. The model is verified using experimental results from present and previous studies for a specific case of choking flow past a two-dimensional prismatic body.

Simulation of Two-Dimensional Turbulent Recirculating Flow Field Behind a V-Shaped Bluff Body

1994 ◽  
Author(s):  
Z. Gu ◽  
M. A. R. Sharif
Keyword(s):  
Flow Field ◽  
Bluff Body ◽  
Flame Stabilization ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Combustion Chambers ◽  
Recirculating Flow ◽  
Conservative Form ◽  
Curvilinear Grid ◽  
Predictor Corrector

Abstract The two-dimensional turbulent recirculating flow fields behind a V-shaped bluff body have been investigated numerically. Similar bluff bodies are used in combustion chambers for flame stabilization. The governing transport equations in conservative form are solved by a pressure based predictor-corrector method. The standard k-ϵ turbulence closure model and a boundary fitted multi-block curvilinear grid system are used in the computation. The code is validated against turbulent flow over a backward facing step problem. The predicted flow field behind the bluff body is also compared with experiment. It is found that while the qualitative features of the flow are well predicted, there is quantitative disagreement between the measurement and prediction. This disagreement can be partially attributed to the k-ϵ turbulence model which is known to be inadequate for recirculating flows. Parametric investigation of the flow field by varying the shape and size of the bluff body is also performed and the results are reported.

scholarly journals Coupling Quasi-Two-Dimensional Friction Model and Discrete Vapor Cavity Model for Simulation of Transient Cavitating Flows in Pipeline Systems

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Qiang Sun ◽  
Yuebin Wu ◽  
Ying Xu ◽  
Liang Chen ◽  
Tae Uk Jang
Keyword(s):  
Cost Effective ◽  
Friction Model ◽  
Experimental Results ◽  
Complex Nature ◽  
Two Dimensional ◽  
Cavity Model ◽  
Cavitating Flows ◽  
Vapor Cavity ◽  
Proposed Model ◽  
Pipeline Systems

Accurate simulation of cavitating flows in pipeline systems is important for cost-effective surge protection. However, this is still a challenge due to the complex nature of the problem. This paper presents a numerical model that combines the discrete vapor cavity model (DVCM) with the quasi-two-dimensional (quasi-2D) friction model to simulate transient cavitating flows in pipeline systems. The proposed model is solved by the method of characteristics (MOC), and the performance is investigated through a numerical case study formulated based on a laboratory pipeline reported in the literature. The results obtained by the proposed model are compared with those calculated by the classic one-dimensional (1D) friction model with the DVCM and the corresponding experimental results provided by the literature, respectively. The comparison shows that the pressure peak, waveform, and phase of pressure pulsations predicted by the proposed model are closer to the experimental results than those obtained by the classic 1D model. This demonstrates that the proposed model that combines the quasi-2D friction model with the DVCM has provided a solution to more accurately simulate transient cavitating flows in pipeline systems.

A Free-Streamline Model for Bluff Bodies in Confined Flow

1977 ◽  
Vol 99 (3) ◽  
pp. 585-592 ◽  
Author(s):  
V. J. Modi ◽  
S. E. El-Sherbiny
Keyword(s):  
Potential Flow ◽  
Bluff Body ◽  
Flow Model ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Flat Plates ◽  
Surface Loading ◽  
Confined Flow ◽  
Potential Flow Model

A potential flow model is presented for two-dimensional symmetrical bluff bodies under wall confinement. It provides a procedure for predicting surface loading on a bluff body over a range of blockage ratios. Experimental results with normal flat plates and circular cylinders for blockage ratios up to 35.5 percent substantiate the validity of the approach.

scholarly journals Two-Dimensional Coupled Vortex-Induced Vibration of Circular Cylinder: Prediction and Extraction of Hydrodynamics Properties

2013 ◽  
Author(s):  
Hossein Zanganeh ◽  
Narakorn Srinil
Keyword(s):  
Circular Cylinder ◽  
Numerical Solutions ◽  
Cross Flow ◽  
Structural Equations ◽  
Experimental Results ◽  
High Mass ◽  
Two Dimensional ◽  
Fluid Structure ◽  
Vortex Induced Vibration ◽  
Proposed Model

An advanced model for predicting a two-dimensional coupled cross-flow and in-line vortex-induced vibration (VIV) of a flexibly-mounted circular cylinder in a uniform flow is proposed and investigated. Attention is placed on a systematic extraction of variable hydrodynamics properties associated with a bi-directional fluid-structure interaction system. The governing equations of motion are based on double Duffing-van der Pol (structural-wake) oscillators with the two structural equations containing cubic and quadratic nonlinear terms. The cubic nonlinearities capture the geometrical coupling of cross-flow/in-line displacements excited by hydrodynamic lift/drag forces whereas the quadratic nonlinearities allow fluid-structure interactions. The combined analytical and numerical solutions of the proposed model are established. By varying flow velocities in numerical simulations, the derived low-order model qualitatively captures several key VIV characteristics of coupled in-line/cross-flow oscillations. By making use of a newly-derived empirical formula, the predicted maximum cross-flow/in-line VIV amplitudes and associated lock-in ranges compare well with several experimental results for cylinders with low/high mass or damping ratios. Moreover, such important hydrodynamic properties as VIV-induced mean drag, added mass, excitation and damping terms can be systematically determined via the proposed model and compared well with some experimental results in the literature.

Testing Three-Dimensional Bluff-Body Models in a Low-Speed Two-Dimensional Adaptive Wall Test Section

1995 ◽  
Vol 117 (4) ◽  
pp. 546-551 ◽  
Author(s):  
D. Sumner ◽  
E. Brundrett
Keyword(s):  
Drag Coefficient ◽  
Test Section ◽  
Bluff Body ◽  
Three Dimensional ◽  
Correction Method ◽  
Blockage Ratio ◽  
Two Dimensional ◽  
Interference Effects ◽  
Low Speed ◽  
Straight Wall

Thin, sharp-edged disk models were evaluated in a low-speed two-dimensional adaptive flexible wall test section to determine the optimum adaptive wall testing environment for three-dimensional bluff-body models, by providing model testing recommendations for nominal solid blockage ratio and model span ratio. Drag coefficient measurements obtained under straight wall and adapted wall conditions showed that for a two-dimensional adaptive wall test section, the model span ratio imposes a more severe restriction upon model size than does the nominal solid blockage ratio. Minimum wall interference conditions were achieved with adapted walls for nominal solid blockage ratios less than 3 percent and model span ratios less than 21 percent, independent of the nominal test section aspect ratio, based on favorable comparison with previously-published experimental data. Data obtained under straight wall conditions confirmed that wall interference effects can only be neglected in conventional, straight-walled test sections for solid blockage ratios less than 0.5 percent and model span ratios less than 10 percent. The post-test boundary correction method of Maskell was successfully used to adjust the straight wall test section drag coefficient measurements of the larger models for wall interference effects, but no direct measurements of wall interference are used with this method. The results support the careful use of a two-dimensional wall adjustment strategy for three-dimensional nonlifting flows.

Aerodynamic behaviour of bodies in the wakes of other bodies

1971 ◽  
Vol 269 (1199) ◽  
pp. 425-437 ◽  
Keyword(s):  
Bluff Body ◽  
Three Dimensional ◽  
Future Research ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Limited Information ◽  
Irrotational Flow ◽  
Two Bodies

Wakes of two-dimensional bluff bodies are described, with emphasis on the properties of the wake which influence the loads on other bodies placed in the wake. The unsteady irrotational flow outside the true wake is included in the discussion. Some limited information on the wakes of three-dimensional bluff bodies is also considered. The interaction between two bodies is subdivided into two categories: (i) when the bodies are close together and the upstream body is influenced by the downstream one and (ii) when the bodies are so far apart that only the downstream body is affected. Experiments are described in which the load on an aerofoil in the wake of a two-dimensional bluff body was measured. The results are presented in the form of an aerodynamic admittance and these experiments are used to illustrate the type of problem associated with the determination of the loads on a bluff body in a wake. Experiments are also described which show the large variation of time-averaged load which can be developed on a body which is part of a closely packed complex of bodies, as the orientation of the complex to the wind is varied. Finally, some ideas for future research are outlined.

scholarly journals Small-scale turbulence characteristics of two-dimensional bluff body wakes

2002 ◽  
Vol 459 ◽  
pp. 67-92 ◽  
Author(s):  
R. A. ANTONIA ◽  
T. ZHOU ◽  
G. P. ROMANO
Keyword(s):  
Porous Body ◽  
Large Scale ◽  
Bluff Body ◽  
Inertial Range ◽  
Small Scale ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
The Difference ◽  
Scale Turbulence ◽  
Made In

Measurements have been made in nominally two-dimensional turbulent wakes generated by five different bluff bodies. Each wake has a different level of large-scale organization which is reflected in different amounts of large-scale anisotropy. Structure functions of streamwise (u) and lateral (v) velocity fluctuations at approximately the same value of Rλ, the Taylor microscale Reynolds number, indicate that inertial-range scales are significantly affected by the large-scale anisotropy. The effect is greater on v than u and more pronounced for the porous-body wakes than the solid-body wakes. In particular, ‘relative’ values of the scaling (or power-law) exponents indicate that the magnitude of the transverse exponents can exceed that of the longitudinal ones in the porous-body wakes. This is supported by the inertial-range behaviour of the spectra of u and v. The difference between the transverse and longitudinal exponents appears to depend on the large-scale anisotropy of the flow, as measured by the ratio of the variances of v and u and ratio of the integral length scales of v and u. The spanwise vorticity spectra are much less affected by the anisotropy than the spectra of u and v.

Computational and Neuro-Fuzzy Study of the Effect of Small Objects on the Flow and Thermal Fields of Bluff Bodies

2006 ◽  
Author(s):  
Ahmed F. Abdel Gawad
Keyword(s):  
Drag Reduction ◽  
Bluff Body ◽  
Three Dimensional ◽  
The Body ◽  
Bluff Bodies ◽  
Small Object ◽  
Two Dimensional ◽  
Neuro Fuzzy ◽  
Body Cooling ◽  
Two Dimensional Flows

The aim of the present study is to find computationally the optimum parameters that affect the drag reduction of bluff bodies using a small object (obstacle). These parameters include the size of the obstacle as well as the gap between the obstacle and the bluff body. Two- and three-dimensional bodies were investigated in turbulent flow fields. The research was focused on the cases of the rectangular-section obstacle. Four values of the obstacle size were studied, namely: 4%, 10%, 35%, and 100% of the size of the bluff body. The effect of the obstacle on the thermal field of the two-dimensional body was also studied. Comparisons were carried out with the available experimental measurements. A proposed neuro-fuzzy approach was used to predict the drag reduction of the entire system. Results showed that system drag reductions up to 62% (two-dimensional flows) and 48% (three-dimensional flows) can be obtained. Also, enhancement of the body cooling up to 75% (two-dimensional flows) may be achieved. Generally, useful comments and suggestions are stated.

Characteristics of Bluff Body Stabilized Turbulent Premixed Flames

2011 ◽  
Author(s):  
Alejandro M. Briones ◽  
Balu Sekar ◽  
Hugh Thornburg
Keyword(s):  
Bluff Body ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reacting Flows ◽  
Chemical Mechanism ◽  
Reacting Flow ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
Aspect Ratios ◽  
Trailing Edges

Non-reacting and reacting flows past typical flameholders are modeled with URANS and LES. The continuity, momentum, energy, species, and turbulence governing equations are solved using two- and three-dimensional configurations. Either 2-step global or 44-step reduced chemical mechanism for C3H8-air combustion, accounting for turbulence-chemistry interaction, and with temperature- and species-dependent thermodynamic and transport properties is utilized. For square and rectangular bluff bodies the flow separates at the leading edges, whereas for triangular bluff body separation occurs only at the trailing edges. These bluff bodies exhibit two shear layers at the trailing edges that shed asymmetric vortices. For rectangular bluff bodies with aspect ratios (AR) less than 2.3 there is backflow from the wake. With increasing AR from unity, backflow is gradually diminished, and the von Ka´rma´n Strouhal number (StvK) decreases. For 2.0<AR<2.3, StvK jumps to a higher value and separation again occurs at the trailing edges for AR = 2.3. Further increase in AR decreases StvK again. The simulations with URANS qualitatively and quantitatively match experimental results for StvK vs. AR. Quantitative discrepancies are, however, found for AR≥2.3. In addition, two-dimensional non-reacting flows with URANS are sufficient to predict StvK. Moreover, two-dimensional simulations of reacting flow indicate that the flame promotes static and dynamic stability for AR = 1.0 and 2.3. The flame is dynamically unstable for AR = 2.0, exhibiting a von Ka´rma´n flow pattern. Stable flames anchored at the most downstream separation location (e.g., the flame anchored at AR = 1.0 is attached to the leading edge, whereas that of AR = 2.3 is attached to the trailing edge). Realizable k-ε URANS and LES simulations for the triangular cylinder closely match the experimental StvK for both non-reacting and reacting flows. Nonetheless, LES predicts a smaller recirculation length than k-ε URANS. LES predicts a flow field in which Be´rnard/von Ka´rma´n (BvK) instability is suppressed, whereas URANS predicts a competition between the Kelvin-Helmholtz (KH) instability and BvK.

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