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Investigation Of Airfoil Boundary Layer And Turbulent Wake Development At Low Reynolds Numbers
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Book Synopsis Investigation of Airfoil Boundary Layer and Turbulent Wake Development at Low Reynolds Numbers by : Serhiy Yarusevych
Download or read book Investigation of Airfoil Boundary Layer and Turbulent Wake Development at Low Reynolds Numbers written by Serhiy Yarusevych and published by . This book was released on 2006 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt: Boundary layer and wake development on a NACA 0025 airfoil at low Reynolds numbers was studied experimentally via surface pressure measurements, hot-wire velocity measurements, and flow visualization. Wind tunnel experiments were carried out for a range of Reynolds numbers and three angles of attack. In addition, flow control with periodic excitations was investigated and a shear layer stability analysis was performed. Two boundary layer flow regimes were identified: (1) boundary layer separation without reattachment and (2) separation bubble formation. The results have demonstrated that transition to turbulence, which occurs due to the amplification of disturbances in the separated shear layer, plays a key role in boundary layer reattachment. Once disturbances reach sufficient amplitude, shear layer roll-up occurs and the resulting vortices are shed at a fundamental frequency. The roll-up process is attributed to the Kelvin-Helmholtz instability, and the salient characteristics of the roll-up vortices can be adequately estimated by means of inviscid linear stability analysis. The final stage of transition is associated with the growth of a sub-harmonic component in the velocity spectrum, which can be attributed to the merging of the roll-up vortices. Wake vortices form in the near-wake region and are shed alternatively on the upper and lower sides of the turbulent wake. Each of the two identified flow regimes is associated with distinctly different characteristics of both the roll-up and wake vortices. It has been established that the fundamental frequency of the shear-layer disturbances exhibits a power law dependency on the Reynolds number, whereas the wake vortex shedding frequency displays a linear dependency on the Reynolds number. A universal scaling for the wake vortex shedding frequency has been determined, which has a universal Strouhal number of 0.17. The results provide added insight into flow control with external acoustic excitation. It is concluded that matching the excitation frequency with the frequency of the most amplified disturbance in the separated shear layer is the optimum method for controlling airfoil performance. Two threshold levels for excitation amplitude have been identified: (i) a minimum effective amplitude that is linked to the background noise level and (ii) a maximum efficient amplitude.
Book Synopsis Low Reynolds Number by : Mustafa Serdar Genç
Download or read book Low Reynolds Number written by Mustafa Serdar Genç and published by BoD – Books on Demand. This book was released on 2012-04-04 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reports the latest development and trends in the low Re number aerodynamics, transition from laminar to turbulence, unsteady low Reynolds number flows, experimental studies, numerical transition modelling, control of low Re number flows, and MAV wing aerodynamics. The contributors to each chapter are fluid mechanics and aerodynamics scientists and engineers with strong expertise in their respective fields. As a whole, the studies presented here reveal important new directions toward the realization of applications of MAV and wind turbine blades.
Book Synopsis Summary of Low Speed Airfoil Data by : Michael S. Selig
Download or read book Summary of Low Speed Airfoil Data written by Michael S. Selig and published by Soartech. This book was released on 1995 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis NACA Wartime Reports. Series L. by : Albert E. Von Doenhoff
Download or read book NACA Wartime Reports. Series L. written by Albert E. Von Doenhoff and published by . This book was released on 1940 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: An extensive series of boundary-layer surveys was made over the surface of an NACA 0012 airfoil at zero lift. The surveys were made at Reynolds numbers, based on the chord, of 2,675,000, 3,780,000, 5,350,000, and 7,550,000. The drag of the airfoil was measured by the wake-survey method throughout a range of Reynolds numbers from 225,000 to 7,560,000. The distribution of skin friction over the surface of the airfoil was found from the boundary-layer surveys and the results are compared with those calculated according to the method of Squire and Young developed in England in 1937.
Book Synopsis Turbulent Wake Development Behind Streamlined Bodies by : B. R. Ramaprian
Download or read book Turbulent Wake Development Behind Streamlined Bodies written by B. R. Ramaprian and published by . This book was released on 1981 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis An Experimental Investigation of Boundary-layer Control for Drag Reduction of a Swept-wing Section at Low Speed and High Reynolds Numbers by : Donald E. Gault
Download or read book An Experimental Investigation of Boundary-layer Control for Drag Reduction of a Swept-wing Section at Low Speed and High Reynolds Numbers written by Donald E. Gault and published by . This book was released on 1960 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Analytical Description of the Complete Two-dimensional Turbulent Boundary-layer Velocity Profile by : David L. Whitfield
Download or read book Analytical Description of the Complete Two-dimensional Turbulent Boundary-layer Velocity Profile written by David L. Whitfield and published by . This book was released on 1977 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: A single analytical expression is derived for the entire (0
Book Synopsis Investigation of Low-speed Turbulent Separated Flow Around Airfoils by :
Download or read book Investigation of Low-speed Turbulent Separated Flow Around Airfoils written by and published by . This book was released on 1987 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Effects of Specific Types of Surface Roughness on Boundary-layer Transition by : Laurence K. Loftin
Download or read book Effects of Specific Types of Surface Roughness on Boundary-layer Transition written by Laurence K. Loftin and published by . This book was released on 1946 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt: Summary: Tests were conducted with two typical low-drag airfoils of 90-inch chord to determine the effects of surface projections, grooves, and sanding scratches on boundary-layer transition. The Reynolds number at which a spanwise row of cylindrical projections would cause premature transition was determined for a range of Reynolds number from approximately 3 x 106 to 10 x 106. Data were obtained for projections of various sizes and chordwise locations on both low-drag airfoils. The results were analyzed on the assumption that the critical airfoil Reynolds number for a given projection was a function only of the local-flow conditions around the projection. This assumption neglected possible effects of tunnel turbulence, pressure gradient, boundary-layer Reynolds number, and the original extent of the laminar flow. The data correlated on the basis of this assumption within a range of critical airfoil Reynolds number of ±0.5 x 106 and within a range of projection height of ±0.002 inch. The tests of surface grooves and sanding scratches indicated that, for the range of Reynolds number investigated, the laminar boundary layer was much less sensitive to surface grooves and sanding scratches than to projections above the surface.
Book Synopsis Investigation of Boundary-layer Reynolds Number for Transition on an NACA 65(215)-114 Airfoil in the Langley Two-dimensional Low-turbulence Pressure Tunnel by : Albert L. Braslow
Download or read book Investigation of Boundary-layer Reynolds Number for Transition on an NACA 65(215)-114 Airfoil in the Langley Two-dimensional Low-turbulence Pressure Tunnel written by Albert L. Braslow and published by . This book was released on 1948 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: A wind-tunnel investigation was made of an NACA 65(215)-114 airfoil to determine the magnitude of the boundary-layer Reynolds number at various positions of transition from laminar to turbulent flow.
Book Synopsis Low Reynolds Number Aerodynamics by : Thomas J. Mueller
Download or read book Low Reynolds Number Aerodynamics written by Thomas J. Mueller and published by Springer Science & Business Media. This book was released on 2013-03-08 with total page 456 pages. Available in PDF, EPUB and Kindle. Book excerpt: Current interest in a variety of low Reynolds number applications has focused attention on the design and evaluation of efficient airfoil sections at chord Reynolds numbers from about 100,000 to about 1,000,000. These applications include remotely piloted vehicles (RPVs) at high altitudes, sailplanes, ultra-light man-carrying/man powered aircraft, mini-RPVs at low altitudes and wind turbines/propellers. The purpose of this conference was to bring together those researchers who have been active in areas closely related to this subject. All of the papers presented are research type papers. Main topics are: Airfoil Design and Analysis, Computational Studies, Stability and Transition, Laminar Separation Bubble, Steady and Unsteady Wind Tunnel Experiments and Flight Experiments.
Book Synopsis A Flight Investigation of Laminar and Turbulent Boundary Layers Passing Through Shock Waves at Full-scale Reynolds Numbers by : Eziaslav N. Harrin
Download or read book A Flight Investigation of Laminar and Turbulent Boundary Layers Passing Through Shock Waves at Full-scale Reynolds Numbers written by Eziaslav N. Harrin and published by . This book was released on 1953 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: An investigation has been made in flight at free-stream Mach numbers up to 0.76 to determine the behavior of laminar and turbulent boundary layers passing through shock waves at Reynolds up to 26,000,000. The free-stream Mach numbers obtained in the tests were sufficiently high to give extensive regions of local supersonic flow. Boundary-layer and pressure-distribution measurements were made on a shoart-span airfoil build around a wing of a fighter airplane. Laminar flow up to the position of the shock wave was obtained on the upper surface of the smooth airfoil. Turbulent flow ahead (upstream) of the shock wave was obtained by attaching a transition strip near the nose.
Book Synopsis Effect of Freestream Turbulence on Laminar Separation Bubbles and Flow Transition on a Low Reynolds Number Airfoil by : Jacob Zilli
Download or read book Effect of Freestream Turbulence on Laminar Separation Bubbles and Flow Transition on a Low Reynolds Number Airfoil written by Jacob Zilli and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effect of freestream turbulence intensity on the laminar separation bubble and flow transition over an SD7003 airfoil was investigated. Measurements were performed for Reynolds numbers ranging from 60,000 to 250,000, various angles of attack and turbulence intensities between 0.05% and 0.99%. Boundary layers with a separation bubble were found to develop a turbulent boundary layer more rapidly than those without. The trends in the skin friction downstream of the peak corresponding to the development of a turbulent boundary layer were very similar for all turbulence intensities, suggesting the turbulent boundary layer forming downstream of transition was not significantly affected by the turbulence intensities investigated. The fluctuating velocity spectra showed that the increase in freestream turbulence intensity introduced sufficient energy to the laminar boundary layer to initiate transition before the flow was able to separate at an angle of attack of 4â Ś but not at 8â Ś.
Book Synopsis The Effects of Freestream Turbulence on Airfoil Boundary Layer Behavior at Low Reynolds Numbers by : David W. Kindelspire
Download or read book The Effects of Freestream Turbulence on Airfoil Boundary Layer Behavior at Low Reynolds Numbers written by David W. Kindelspire and published by . This book was released on 1988 with total page 117 pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental study was conducted to determine the effects of freestream turbulence on airfoil boundary layer behavior. Freestream turbulence intensity levels up to approximately 4% and length scales up to approximately two inches were generated using turbulence-generating grids. Data were collected using a single-wire hot-wire probe in conjunction with a three-dimensional traversing system. Increased levels of freestream turbulence were found to cause correspondingly earlier transition to a turbulent boundary layer. Boundary layer growth was found to be unaffected by freestream turbulence levels up to 4% at length scales an order of magnitude greater than the boundary layer thickness. For length scales on the order of boundary layer thickness, a 12% increase in the turbulent boundary layer thickness was found with an increase in turbulence intensity from 0.23% to 0.5%. Keywords: Theses, Computer programs, Reynolds numbers, Boundary layer, Turbulence, Laminar flow, Transition. (JHD).
Book Synopsis Further Investigation of the Near Wall Flow Structure of a Low Reynolds Number 3-D Turbulent Boundary Layer by : J. L. Fleming
Download or read book Further Investigation of the Near Wall Flow Structure of a Low Reynolds Number 3-D Turbulent Boundary Layer written by J. L. Fleming and published by . This book was released on 1995 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Fixed and Flapping Wing Aerodynamics for Micro Air Vehicle Applications by : Thomas J. Mueller
Download or read book Fixed and Flapping Wing Aerodynamics for Micro Air Vehicle Applications written by Thomas J. Mueller and published by AIAA. This book was released on 2001 with total page 614 pages. Available in PDF, EPUB and Kindle. Book excerpt: This title reports on the latest research in the area of aerodynamic efficency of various fixed-wing, flapping wing, and rotary wing concepts. It presents the progress made by over fifty active researchers in the field.
Book Synopsis Direct Numerical Simulations of a Cambered NACA 65(1)-412 Airfoil at Low Reynolds Numbers by : Bjoern Fabian Klose
Download or read book Direct Numerical Simulations of a Cambered NACA 65(1)-412 Airfoil at Low Reynolds Numbers written by Bjoern Fabian Klose and published by . This book was released on 2021 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation is a comprehensive account of the low-Reynolds number (Re) flow over a cambered airfoil for a wide range of angles of attack with a focus on the dynamics of boundary layer separation and transition. The unsteady and complex phenomena of the transitional flow are analyzed through a combination of direct numerical simulations (DNS), large-eddy simulations (LES), experiments, and development of Lagrangian theory and methods. A discontinuous Galerkin spectral element method (DGSEM) is used to model the compressible Navier-Stokes equations in two and three dimensions. The DGSEM generates high-order accurate results with low dispersion and diffusion errors and has been developed to include kinetic-energy conserving volume fluxes, tools to efficiently track Lagrangian fluid tracers, and computation of higher wall-normal velocity derivatives. The code is benchmarked through a series of Navier-Stokes flows using different DG variants and polynomial orders. High-fidelity DNS in three dimensions show that the transitional flow over a cambered NACA 65(1)-412 airfoil at Re = 20,000 swiftly changes from a state of laminar separation at mid-chord without reattachment to a laminar separation bubble (LSB) at the leading edge with a turbulent boundary layer. The bifurcation occurs within an angle-of-attack change of two degrees and is accompanied by a rapid increase of the lift and decrease of the drag force, which is observed in computations and experiments likewise. Each flow regime is governed by different dynamics, instabilities, and wake structures that change with the transition location of the separated shear layer. The kinematic aspects of flow separation are further investigated in the Lagrangian frame, where the initial motion of upwelling fluid material from the wall is related to the long-term attracting manifolds in the flow field. An objective finite-time diagnostic for instabilities in shear flows based on the curvature of Lagrangian material lines is introduced. By defining a flow instability in the Lagrangian frame as the increased folding of lines of fluid particles, subtle perturbations and unstable growth thereof are detected early based solely on the curvature change of material lines over finite time.
