scholarly journals Experimental and Numerical Study of Flow Structures Associated With Low Aspect Ratio Elliptical Cavities

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Taravat Khadivi ◽  
Eric Savory
Keyword(s):  
Aspect Ratio ◽  
Particle Image ◽  
Numerical Study ◽  
Three Dimensional ◽  
Reynolds Stress Model ◽  
Cavity Flows ◽  
Low Aspect Ratio ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

The flow regimes associated with 2:1 aspect ratio elliptical planform cavities of varying depth immersed in a turbulent boundary layer at a Reynolds number of 8.7 × 104, based on the minor axis of the cavity, have been quantified from particle image velocimetry measurements and three-dimensional steady computational fluid dynamics simulations (Reynolds stress model closure). Although these elliptical cavity flows have some similarities with nominally two-dimensional and rectangular cases, three-dimensional effects due to the low aspect ratio and curvature of the walls give rise to features exclusive to low aspect ratio elliptical cavities, including formation of cellular structures at intermediate depths and vortex structures within and downstream of the cavity.

Scaled Room Three-Dimensional Computational Fluid Dynamics Simulations

2002 ◽  
Author(s):  
Steven P. O’Halloran ◽  
Mohammad H. Hosni ◽  
B. Terry Beck ◽  
Thomas P. Gielda
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Working Fluid ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Simulations ◽  
Computational Fluid Dynamics Cfd ◽  
Dynamics Simulations

Computational fluid dynamics (CFD) simulations were used to predict three-dimensional flow within a one-tenth-scale room. The dimensions of the scaled room were 732 × 488 × 274 mm (28.8 × 19.2 × 10.8 in.) and symmetry was utilized so that only half of the room was modeled. Corresponding measurements were made under isothermal conditions and water was used as the working fluid instead of air. The commercially available software Fluent was used to perform the simulations. Two turbulence models were used: the renormalization group (RNG) k-ε model and the Reynolds-stress model. The CFD setup is presented in this paper, along with the velocity and turbulent kinetic energy results. The simulation results are compared to previously obtained three-dimensional particle image velocimetry (PIV) measurements made within the same scaled room under similar conditions.

Experimental and Numerical Study of the Flow Around a Semi-Submerged Rectangular Cylinder

2012 ◽  
Author(s):  
Tufan Arslan ◽  
Stefano Malavasi ◽  
Bjørnar Pettersen ◽  
Helge I. Andersson
Keyword(s):  
Particle Image ◽  
Model Simulation ◽  
Numerical Study ◽  
Three Dimensional ◽  
Separated Flow ◽  
Piv Measurements ◽  
Rectangular Cylinder ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Cfd

The present work is motivated by phenomena occurring in the flow field around structures partly submerged in water. A three dimensional unsteady flow around a rectangular cylinder is studied for four different submergence ratios by using computational fluid dynamics (CFD) tools with LES turbulence model. Simulation results are compared to particle image velocimetry (PIV) measurements at Reynolds number Re = 12100 and Froude number Fr = 0.26. Focus in our investigation is on the characterization of the behaviour of vortex structures generated by separated flow. Another target in the study is to obtain better knowledge of the hydrodynamic forces acting on a semi-submerged structure. Computed force coefficients are compared with experimental measurements.

Experimental and Numerical Study of Stall Flutter in a Transonic Low-Aspect Ratio Fan Blisk

2003 ◽  
Author(s):  
A. J. Sanders ◽  
K. K. Hassan ◽  
D. C. Rabe
Keyword(s):  
Aspect Ratio ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Strain Gages ◽  
Pressure Transducers ◽  
Low Aspect Ratio ◽  
Benchmark Data

Experiments are performed on a modern design transonic shroudless low-aspect ratio fan blisk that experienced both subsonic/transonic and supersonic stall-side flutter. High-response flush mounted miniature pressure transducers are utilized to measure the unsteady aerodynamic loading distribution in the tip region of the fan for both flutter regimes, with strain gages utilized to measure the vibratory response at incipient and deep flutter operating conditions. Numerical simulations are performed and compared with the benchmark data using an unsteady three-dimensional nonlinear viscous computational fluid dynamic (CFD) analysis, with the effects of tip clearance, vibration amplitude, and the number of time steps-per-cycle investigated. The benchmark data are used to guide the validation of the code and establish best practices that ensure accurate flutter predictions.

scholarly journals Role of the tip vortex in the force generation of low-aspect-ratio normal flat plates

2007 ◽  
Vol 581 ◽  
pp. 453-468 ◽  
Author(s):  
MATTHEW J. RINGUETTE ◽  
MICHELE MILANO ◽  
MORTEZA GHARIB
Keyword(s):  
Aspect Ratio ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Unsteady Motion ◽  
Tip Vortex ◽  
Flat Plates ◽  
Low Aspect Ratio ◽  
Start Up ◽  
Image Velocimetry

We investigate experimentally the force generated by the unsteady vortex formation of low-aspect-ratio normal flat plates with one end free. The objective of this study is to determine the role of the free end, or tip, vortex. Understanding this simple case provides insight into flapping-wing propulsion, which involves the unsteady motion of low-aspect-ratio appendages. As a simple model of a propulsive half-stroke, we consider a rectangular normal flat plate undergoing a translating start-up motion in a towing tank. Digital particle image velocimetry is used to measure multiple perpendicular sections of the flow velocity and vorticity, in order to correlate vortex circulation with the measured plate force. The three-dimensional wake structure is captured using flow visualization. We show that the tip vortex produces a significant maximum in the plate force. Suppressing its formation results in a force minimum. Comparing plates of aspect ratio six and two, the flow is similar in terms of absolute distance from the tip, but evolves faster for aspect ratio two. The plate drag coefficient increases with decreasing aspect ratio.

Cross-Wind Influence on Low Aspect Ratio Wings at Low Reynolds Numbers

2013 ◽  
Author(s):  
Amir Karimi Noughabi ◽  
Mehran Tadjfar
Keyword(s):  
Aspect Ratio ◽  
Numerical Study ◽  
Three Dimensional ◽  
Micro Air Vehicles ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Low Aspect Ratio ◽  
Aspect Ratios ◽  
Lift And Drag ◽  
Lift And Drag Coefficient

The aerodynamics of the low aspect ratio (LAR) wings is of outmost importance in the performance of the fixed-wing micro air vehicles (MAVs). The flow around these wings is widely influenced by three dimensional (3D) phenomena: including wing-tip vortices, formation of laminar bubble, flow separation and reattachment, laminar to turbulent transition or any combination of these phenomena. All the recent studies consider the aerodynamic characteristics of the LAR wings under the effect of the direct wind. Here we focus on the numerical study of the influence of cross-wind on flow over the inverse Zimmerman wings with the aspect ratios (AR) between 1 and 2 at Reynolds numbers between 6×104 and 105. We have considered cross-wind’s angles from 0° to 40° and angle of attack from 0° to 12°. The results show that lift and drag coefficient generally decrease when the angle of the cross-wind is increased.

Aspect ratio effect on electroconvection in a suspended liquid crystal film with a rectangular boundary

2017 ◽  
Vol 828 ◽  
pp. 57-69
Author(s):  
Xuefei Guo ◽  
Yongkang Le ◽  
Bochao Cao
Keyword(s):  
Liquid Crystal ◽  
Stability Analysis ◽  
Aspect Ratio ◽  
Particle Image ◽  
Liquid Films ◽  
Low Aspect Ratio ◽  
Global Stability Analysis ◽  
Aspect Ratios ◽  
Crystal Film ◽  
Image Velocimetry

The aspect ratio dependence of the electroconvection phenomenon in a suspended nematic liquid crystal film with a rectangular boundary is investigated. Two-dimensional global stability analysis is carried out on the coupled electrohydrodynamic system to calculate the instability boundary of the phenomenon for different aspect ratios. The calculated critical $R$ number (Rayleigh-like number) shows a rapidly decreasing trend in the low-aspect-ratio region (roughly $\unicode[STIX]{x1D6FE}<1.5$, where $\unicode[STIX]{x1D6FE}$ is defined as the aspect ratio of the film), and then the variation becomes slow until $\unicode[STIX]{x1D6FE}\approx 2.5$, where the critical $R$ number starts to increase slightly. Convective patterns of liquid films with different aspect ratios are also obtained from stability analysis and validated by particle image velocimetry measurement.

Blade Lean and Shroud Leakage Flows in Low Aspect Ratio Turbines

2008 ◽  
Author(s):  
Budimir Rosic ◽  
Liping Xu
Keyword(s):  
Aspect Ratio ◽  
Numerical Study ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Leakage Flow ◽  
Industrial Practice ◽  
Leakage Flows ◽  
Low Aspect Ratio ◽  
Stator Blade ◽  
Different Levels

Blade lean, i.e. non-radial blade stacking, has been intensively used over the past in the design process of low aspect ratio gas and steam turbines. Although its influence on turbine efficiency is not completely understood, it has been proved as an effective way of controlling blade loading and secondary flows on blade passage endwalls. Three-dimensional blade designs in modern industrial practice are usually carried out using clean endwalls. The influence of the leakage flows on three-dimensional blade design is traditionally neglected. This paper presents an experimental study where two different stator blades, with different levels of compound lean, were tested in a low speed three-stage model turbine with the shroud leakage flow geometry representative of industrial practice. The experimental measurements were compared with numerical tests, conducted on the same blade geometries. The influence of the compound lean on the stator flow field was analysed in detail. In order to analyse the combined effects of both the stator hub and rotor shroud leakage flow on the blade lean, in the second part of the paper a numerical study on a two stage turbine with both leakage flow paths representative of a real turbine was carried out. Performance of three different stator blade designs (two different levels of compound lean and a straight blade) was investigated. The aim of this study is to understand the mechanism and the consequence of the stator blade lean on stage performance in an environment with leakage flows and associated cavities.

Numerical Study of Different Closure Approaches for Prediction of Forced Convective Turbulent Cylindrical Cavity Flows

2016 ◽  
Vol 366 ◽  
pp. 166-181
Author(s):  
Elizaldo Domingues dos Santos ◽  
Marco Paulsen Rodrigues ◽  
Thiago Smith V.C. de Andrade ◽  
Liércio André Isoldi ◽  
Francis Henrique Ramos França ◽  
...  
Keyword(s):  
Turbulent Flows ◽  
Cylindrical Cavity ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Cavity Flows ◽  
Thermal Fields ◽  
Convective Fluxes

The present work exhibits a numerical study comparing the fluid dynamic and thermal fields of turbulent, three-dimensional forced convective cylindrical cavity flows obtained with Large Eddy Simulation (LES) and Reynolds-Averaged Navier Stokes (RANS). In the latter approach, three different closure models are employed: Reynolds Stress Model (RSM), standard k – ε and standard k - ω. It is considered a three-dimensional, incompressible, turbulent fluid flow at the steady state with ReD = 22,000 and Pr = 0.71. The main purpose is to investigate whether discrepancies are noticed in time-averaged and statistics of turbulent flows between LES and RANS predictions. Differences in time-averaged and statistical fields can be important for evaluation of convective fluxes in turbulent flows and combined convective and radiative transfer in participant media, i.e., for study of Turbulence-Radiation Interactions (TRI). The spatially-filtered and time-averaged conservation equations of mass, momentum and energy are solved with the Finite Volume Method (FVM). Results showed that time-averaged and RMS thermal fields obtained with LES and RANS presented reasonable discrepancies in regions near the cavity surfaces, which affects the convective fluxes in this region. For the highest temperature region of the cavity (near its inlet) the predictions obtained with LES and RANS are similar, which can led to similar predictions in heat exchange when thermal radiation is taken into account in optically thin participant media. For optically thick media, where local differences increase their importance, the employment of RANS is not recommended.

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