A Study of Turbulent Wakes with and Without the Presence of Free Stream Turbulence PDF Download
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Author: Mahmoud K. Ardebili
Publisher:
ISBN:
Category : Turbulence
Languages : en
Pages : 444
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Author: Mahmoud K. Ardebili
Publisher:
ISBN:
Category : Turbulence
Languages : en
Pages : 444
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Author: Jack Medzorian
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Wall-bounded tip vortices appear in a variety of aerodynamic applications, such as, aircraft engines, inlet S-ducts, turbomachinery tip leakage, and vortex generators used for flow separation control. Studies show that vortex flows with high swirl that are exposed to a sufficient adverse pressure gradient will trigger the onset of vortex instability. However, it is not known whether the addition of freestream turbulence or the presence of a wall will stabilize a vortex due to momentum entrainment or trigger early bursting via amplification of an instability pathway. In this study, a wall-bounded vortex is analyzed in a low-speed wind tunnel to evaluate the effects that adverse pressure gradient and freestream turbulence have on vortex stability boundaries. Experimental techniques such as high-speed stereoscopic particle image velocity is used to capture three-dimensional flow fields of the wall bounded vortex. In addition to the PIV measurements, point measurements are taken using Laser Doppler Velocimetry to obtain turbulent characterization of the freestream and boundary layer flow. The results in this study predict an increase in vortex stability with freestream turbulence. Near a wall, further increases in vortex stability is depicted due to increased diffusion and reduction in rotational momentum. Furthermore, turbulent kinetic energy in a vortex core is decreased in high freestream turbulence when the vortex is near a wall due to a reduction in roll up and entrainment of high turbulence that exists in turbulent boundary layers near the wall. Turbulent boundary layers exposed to high freestream turbulence and adverse pressure gradients appear in a variety of aerodynamic application such as the suction side of airfoils within gas turbine engines and on aircraft wings. Non-equilibrium turbulent boundary layers exposed to a non-constant adverse pressure gradient have been shown to influence the outer region of the mean boundary layer profile due to the resilience of larger scale superstructures. However, it is not known whether the addition of freestream turbulence will increase the effect of history in a turbulent boundary layer due to increased entrainment of larger scales or decrease in effects from breakdown of these superstructures in the freestream. In this study, an experimental technique known as laser Doppler velocimetry is applied to obtain 2-dimensional, high-speed velocity measurements used for capturing mean profiles, turbulent statistics, and turbulent characterization of the freestream flow. The results in this study predict that pressure gradient history effects can have influence on Reynolds stress distributions past the outer region and into the log-region of the boundary layer due to diffusion of turbulence towards the wall. Additionally, pressure gradient effects, and thus the effects of a boundary layer's history, are significantly reduced when subjected to freestream turbulence due to dominant influence of turbulence within the wake region. Lastly, turbulent statistics show that a straight contoured wall, containing a smaller local pressure gradient but sustained over longer distance, has a greater adverse pressure gradient effect on a boundary relative to concave or convex contouring.
Author: Bernhard Stoevesandt
Publisher: Springer Nature
ISBN: 3030313077
Category : Technology & Engineering
Languages : en
Pages : 1495
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Book Description
This handbook provides both a comprehensive overview and deep insights on the state-of-the-art methods used in wind turbine aerodynamics, as well as their advantages and limits. The focus of this work is specifically on wind turbines, where the aerodynamics are different from that of other fields due to the turbulent wind fields they face and the resultant differences in structural requirements. It gives a complete picture of research in the field, taking into account the different approaches which are applied. This book would be useful to professionals, academics, researchers and students working in the field.
Author: Salamon Eskinazi
Publisher:
ISBN:
Category : Cylinders
Languages : en
Pages : 58
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Author: Thomas R. Steiner
Publisher:
ISBN:
Category : Reynolds stress
Languages : en
Pages : 694
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Author: A.S. Ginevsky
Publisher: Springer Science & Business Media
ISBN: 3642017606
Category : Mathematics
Languages : en
Pages : 166
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Book Description
Investigation of vortex wakes behind various aircraft, especially behind wide bodied and heavy cargo ones, is of both scientific and practical in terest. The vortex wakes shed from the wing’s trailing edge are long lived and attenuate only atdistances of10–12kmbehindthe wake generating aircraft. The encounter of other aircraft with the vortex wake of a heavy aircraft is open to catastrophic hazards. For example, air refueling is adangerous operationpartly due to thepossibility of the receiver aircraft’s encountering the trailing wake of the tanker aircraft. It is very important to know the behavior of vortex wakes of aircraft during theirtakeoff andlanding operations whenthe wakes canpropagate over the airport’s ground surface and be a serious hazard to other depart ing or arriving aircraft. This knowledge can help in enhancing safety of aircraft’s movements in the terminal areas of congested airports where the threat of vortex encounters limits passenger throughput. Theoreticalinvestigations of aircraft vortex wakes arebeingintensively performedinthe major aviationnations.Usedforthispurpose are various methods for mathematical modeling of turbulent flows: direct numerical simulation based on the Navier–Stokes equations, large eddy simulation using the Navier–Stokes equations in combination with subrigid scale modeling, simulation based on the Reynolds equations closed with a differential turbulence model. These approaches are widely used in works of Russian and other countries’ scientists. It should be emphasized that the experiments in wind tunnels and studies of natural vortex wakes behind heavy and light aircraft in flight experiments are equally important.
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781721940462
Category :
Languages : en
Pages : 254
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Experimental results from a study of the effects of passing wakes upon laminar-to-turbulent transition in a low-pressure turbine passage are presented. The test section geometry is designed to simulate the effects of unsteady wakes resulting from rotor-stator interaction upon laminar-to-turbulent transition in turbine blade boundary layers and separated flow regions over suction surfaces. Single-wire, thermal anemometry techniques were used to measure time-resolved and phase-averaged, wall-normal profiles of velocity, turbulence intensity, and intermittency at multiple streamwise locations over the turbine airfoil suction surface. These data are compared to steady state, wake-free data collected in the same geometry to identify the effects of wakes upon laminar-to-turbulent transition. Results are presented for flows with a Reynolds number based on suction surface length and exit velocity of 50,000 and an approach flow turbulence intensity of 2.5 percent. From these data, the effects of passing wakes and associated increased turbulence levels and varying pressure gradients on transition and separation in the near-wall flow are presented. The results show that the wakes affect transition both by virtue of their difference in turbulence level from that of the free-stream but also by virtue of their velocity deficit relative to the freestream velocity, and the concomitant change in angle of attack and temporal pressure gradients. The results of this study seem to support the theory that bypass transition is a response of the near-wall viscous layer to pressure fluctuations imposed upon it from the free-stream flow. The data also show a significant lag between when the wake is present over the surface and when transition begins. The accompanying CD-ROM includes tabulated data, animations, higher resolution plots, and an electronic copy of this report. Kaszeta, Richard W. and Simon, Terrence W. and Ashpis, David (Technical Monitor) Glenn Research Center NCC3-652; RTOP 71
Author:
Publisher:
ISBN:
Category : Research
Languages : en
Pages : 48
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Author: Bruno Eckhardt
Publisher: Springer Science & Business Media
ISBN: 3642030858
Category : Science
Languages : en
Pages : 973
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Book Description
This volume comprises the communications presented at the EUROMECH European Turbulence Conference ETC12, held in Marburg in September 2009. The topics covered by the meeting include: Acoustics of turbulent flows, Atmospheric turbulence, Control of turbulent flows, Geophysical and astrophysical turbulence, Instability and transition, Intermittency and scaling, Large eddy simulation and related techniques, Lagrangian aspects, MHD turbulence, Reacting and compressible turbulence, Transport and mixing, Turbulence in multiphase and non-Newtonian flows, Vortex dynamics and structure, formation, Wall bounded flows.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 704
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