Physics of Separated Flow Over a NACA 0015 Airfoil and Detection of Flow Separation

2009 ◽  
Author(s):  
W L Siauw ◽  
J Bonnet ◽  
J Tensi ◽  
L Cattafesta
Keyword(s):  
Flow Separation ◽  
Separated Flow ◽  
Naca 0015

scholarly journals Numerical analysis of high-lift configurations with oscillating flaps

2021 ◽  
Author(s):  
Johannes Ruhland ◽  
Christian Breitsamter
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Separated Flow ◽  
Navier Stokes ◽  
Rotational Axis ◽  
High Lift ◽  
Hinge Point ◽  
Reduced Frequency ◽  
Flap Deflection ◽  
The Impact

AbstractThis study presents two-dimensional aerodynamic investigations of various high-lift configuration settings concerning the deflection angles of droop nose, spoiler and flap in the context of enhancing the high-lift performance by dynamic flap movement. The investigations highlight the impact of a periodically oscillating trailing edge flap on lift, drag and flow separation of the high-lift configuration by numerical simulations. The computations are conducted with regard to the variation of the parameters reduced frequency and the position of the rotational axis. The numerical flow simulations are conducted on a block-structured grid using Reynolds Averaged Navier Stokes simulations employing the shear stress transport $$k-\omega $$ k - ω turbulence model. The feature Dynamic Mesh Motion implements the motion of the oscillating flap. Regarding low-speed wind tunnel testing for a Reynolds number of $$0.5 \times 10^{6}$$ 0.5 × 10 6 the flap movement around a dropped hinge point, which is located outside the flap, offers benefits with regard to additional lift and delayed flow separation at the flap compared to a flap movement around a hinge point, which is located at 15 % of the flap chord length. Flow separation can be suppressed beyond the maximum static flap deflection angle. By means of an oscillating flap around the dropped hinge point, it is possible to reattach a separated flow at the flap and to keep it attached further on. For a Reynolds number of $$20 \times 10^6$$ 20 × 10 6 , reflecting full scale flight conditions, additional lift is generated for both rotational axis positions.

scholarly journals Flow Separation Control of Backward-Facing Step Airfoil NACA0015 by Blowing Technique

2019 ◽  
Vol 12 (1) ◽  
pp. 99-119
Author(s):  
Khuder N. Abed
Keyword(s):  
Flow Separation ◽  
Numerical Study ◽  
Leading Edge ◽  
Distribution Coefficients ◽  
Open Circuit ◽  
Experimental Investigations ◽  
Backward Facing Step ◽  
Ansys Fluent ◽  
Flow Separation Control ◽  
Naca 0015

The aim of this paper is to control the flow separation above backward-facing step (BFS) airfoil type NACA 0015 by blowing method. The flow field over airfoil has been studied both experimentally and computationally. The study was divided into two parts: a practical study through which NACA 0015 type with a backward -facing step (located at 44.4% c from leading edge) on the upper surface containing blowing holes parallel to the airfoil chord was used. The tests were done over two-dimensional airfoil in an open circuit suction subsonic wind tunnel with flow velocity 25m/s to obtain the pressure distribution coefficients. A numerical study was done by using ANSYS Fluent software version 16.0 on three models of NACA 0015, the first one has backward-facing step without blowing, the second with single blowing holes and the third have multi blowing holes technique. Both studies (experimental and numerical) were done at low Reynolds number (Re=4.4x105) and all models have chord length 0.27m.The experimental investigations and CFD simulations have been performed on the same geometry dimensions, it has been observed that the flow separation on the airfoil can be delayed by using  velocity blowing (30m/s) on the upper surface. The multi blowing holes with velocity improved the aerodynamics properties.The multi blowing holes and single blowing hole thesame effect onpressure distribution coefficients

Highly resolved experimental results of the separated flow in a channel with streamwise periodic constrictions

2016 ◽  
Vol 796 ◽  
pp. 257-284 ◽  
Author(s):  
Christian J. Kähler ◽  
Sven Scharnowski ◽  
Christian Cierpka
Keyword(s):  
Turbulent Flow ◽  
Flow Separation ◽  
Flow Direction ◽  
Separated Flow ◽  
Mean Flow ◽  
Complex Flow ◽  
Flow Measurements ◽  
Flow Features ◽  
Wall Flow ◽  
Near Wall

The understanding and accurate prediction of turbulent flow separation on smooth surfaces is still a challenging task because the separation and the reattachment locations are not fixed in space and time. Consequently, reliable experimental data are essential for the validation of numerical flow simulations and the characterization and analysis of the complex flow physics. However, the uncertainty of the existing near-wall flow measurements make a precise analysis of the near-wall flow features, such as separation/reattachment locations and other predicted near-wall flow features which are under debate, often impossible. Therefore, the periodic hill experiment at TU Munich (ERCOFTAC test case 81) was repeated using high resolution particle image velocimetry and particle tracking velocimetry. The results confirm the strong effect of the spatial resolution on the near-wall flow statistics. Furthermore, it is shown that statistically stable values of the turbulent flow variables can only be obtained for averaging times which are challenging to realize with highly resolved large eddy simulation and direct numerical simulation techniques. Additionally, the analysis implies that regions of correlated velocity fluctuations with rather uniform streamwise momentum exist in the flow. Their size in the mean flow direction can be larger than the hill spacing. The possible impact of the correlated turbulent motion on the wake region is discussed, as this interaction might be important for the understanding and control of the flow separation dynamics on smooth bodies.

scholarly journals NARMAX Identification Based Closed-Loop Control of Flow Separation over NACA 0015 Airfoil

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 100
Author(s):  
Sohaib Obeid ◽  
Goodarz Ahmadi ◽  
Ratneshwar Jha
Keyword(s):  
Flow Separation ◽  
Closed Loop ◽  
Lift Coefficient ◽  
Open Loop ◽  
Synthetic Jet ◽  
Function Technique ◽  
Closed Loop Control ◽  
Pressure Data ◽  
Loop Control ◽  
Naca 0015

A closed-loop control algorithm for the reduction of turbulent flow separation over NACA 0015 airfoil equipped with leading-edge synthetic jet actuators (SJAs) is presented. A system identification approach based on Nonlinear Auto-Regressive Moving Average with eXogenous inputs (NARMAX) technique was used to predict nonlinear dynamics of the fluid flow and for the design of the controller system. Numerical simulations based on URANS equations are performed at Reynolds number of 106 for various airfoil incidences with and without closed-loop control. The NARMAX model for flow over an airfoil is based on the static pressure data, and the synthetic jet actuator is developed using an incompressible flow model. The corresponding NARMAX identification model developed for the pressure data is nonlinear; therefore, the describing function technique is used to linearize the system within its frequency range. Low-pass filtering is used to obtain quasi-linear state values, which assist in the application of linear control techniques. The reference signal signifies the condition of a fully re-attached flow, and it is determined based on the linearization of the original signal during open-loop control. The controller design follows the standard proportional-integral (PI) technique for the single-input single-output system. The resulting closed-loop response tracks the reference value and leads to significant improvements in the transient response over the open-loop system. The NARMAX controller enhances the lift coefficient from 0.787 for the uncontrolled case to 1.315 for the controlled case with an increase of 67.1%.

Hypersonic Flow Separation in Shock Wave Boundary Layer Interactions

1992 ◽  
Author(s):  
A. Hamed ◽  
Ajay Kumar
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Flow Separation ◽  
Characteristic Length ◽  
Separated Flow ◽  
Surface Cooling ◽  
Flat Plates ◽  
Shock Interactions ◽  
Wave Boundary ◽  
Incipient Separation

This work presents an assessment of the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consist of selected configurations where the only characteristic length in the interation is the incoming boundary layer thickness. It consists of two dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the empirical correlations for incipient separation are reviewed. The effects of Mach number, Reynolds number, surface cooling and the methods of detecting separation are discussed.

Heat Transfer from a Plate Elevated above a Host Surface and Washed by a Separated Flow Induced by the Elevation Step

1981 ◽  
Vol 103 (3) ◽  
pp. 441-447 ◽  
Author(s):  
E. M. Sparrow ◽  
F. Samie ◽  
S. C. Lau
Keyword(s):  
Heat Transfer ◽  
Flow Separation ◽  
Angle Of Attack ◽  
Separated Flow ◽  
Active Surface ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Reynolds Number Flow ◽  
Heat Transfer Coefficients ◽  
High Reynolds

Wind tunnel experiments were performed to determine heat transfer coefficients and fluid flow patterns for a thermally active surface elevated above a parallel host surface. The step-like blockage associated with the elevation causes flow separation and recirculation on the forward portion of the thermally active surface. Four parameters were varied during the course of the experiments, including the angle of attack of the oncoming airflow relative to the surface, the step height, the extent of the host surface which frames the active surface (i.e., the skirt width), and the Reynolds number. Flow visualization studies, performed with the oil-lampblack technique, showed that the streamwise extent of the separation zone increases with decreasing angle of attack, with larger step heights and skirt widths, and at higher Reynolds numbers. At larger angles of attack, separation does not occur. The experimentally determined heat transfer coefficients were found to increase markedly due to the flow separation, and separation-related enhancements as large as a factor of two were encountered. The enhancement was accentuated at small angles of attack, at large step heights and skirt widths, and at high Reynolds numbers. A main finding of the study is that the separation-affected heat transfer coefficients are generally greater than those for no separation, so that the use of the latter may underestimate the heat transfer rates. For an application such as a retrofit solar collector, such an underestimation of the wind-related heat loss would yield an optimistic prediction of the collector efficiency.

Large Eddy Simulation and CDNS Investigation of T106C Low-Pressure Turbine

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Site Hu ◽  
Chao Zhou ◽  
Zhenhua Xia ◽  
Shiyi Chen
Keyword(s):  
Large Eddy Simulation ◽  
Flow Separation ◽  
Separated Flow ◽  
Low Pressure ◽  
Secondary Flows ◽  
Computational Domain ◽  
Suction Surface ◽  
Low Pressure Turbine ◽  
Eddy Simulation ◽  
Large Eddy

This study investigates the aerodynamic performance of a low-pressure turbine, namely the T106C, by large eddy simulation (LES) and coarse grid direct numerical simulation (CDNS) at a Reynolds number of 100,000. Existing experimental data were used to validate the computational fluid dynamics (CFD) tool. The effects of subgrid scale (SGS) models, mesh densities, computational domains and boundary conditions on the CFD predictions are studied. On the blade suction surface, a separation zone starts at a location of about 55% along the suction surface. The prediction of flow separation on the turbine blade is always found to be difficult and is one of the focuses of this work. The ability of Smagorinsky and wall-adapting local eddy viscosity (WALE) model in predicting the flow separation is compared. WALE model produces better predictions than the Smagorinsky model. CDNS produces very similar predictions to WALE model. With a finer mesh, the difference due to SGS models becomes smaller. The size of the computational domain is also important. At blade midspan, three-dimensional (3D) features of the separated flow have an effect on the downstream flows, especially for the area near the reattachment. By further considering the effects of endwall secondary flows, a better prediction of the flow separation near the blade midspan can be achieved. The effect of the endwall secondary flow on the blade suction surface separation at the midspan is explained with the analytical method based on the Biot–Savart Law.

Flow Separation in Shock Wave Boundary Layer Interactions

1994 ◽  
Vol 116 (1) ◽  
pp. 98-103 ◽  
Author(s):  
A. Hamed ◽  
A. Kumar
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Flow Separation ◽  
Characteristic Length ◽  
Separated Flow ◽  
Surface Cooling ◽  
Flat Plates ◽  
Shock Interactions ◽  
Wave Boundary ◽  
Incipient Separation

This work presents an assessment of the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consists of selected configurations where the only characteristic length in the iteration is the incoming boundary layer thickness. It consists of two-dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the empirical correlations for incipient separation are reviewed. The effects of Mach number, Reynolds number, surface cooling, and the methods of detecting separation are discussed.

Active Flow Control of Separated Turbulent Flow Over a Hump Using RANS, DES, and LES

2008 ◽  
Author(s):  
Subhadeep Gan ◽  
Urmila Ghia ◽  
Karman Ghia
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Flow Separation ◽  
Turbulence Modeling ◽  
Active Flow Control ◽  
Separated Flow ◽  
Experimental Results ◽  
Complex Flow ◽  
Active Flow ◽  
Turbulent Separated Flow

Most practical flows in engineering applications are turbulent, and exhibit separation. Losses due to separation are undesirable because they generally have adverse effects on performance and efficiency. Therefore, control of turbulent separated flows has been a topic of significant interest as it can reduce separation losses. It is of utmost importance to understand the complex flow dynamics that leads to flow separation and come up with methods of flow control. In the past, passive flow-control was mostly implemented that does not require any additional energy source to reduce separation losses but it leads to increasing viscous losses at higher Reynolds number. More recent work has been focused primarily on active flow-control techniques that can be turned on and off depending on the requirement of flow-control. The present work is focused on implementing flow control using steady suction in the region of flow separation. The present work is Case 3 of the 2004 CFD Validation on Synthetic Jets and Turbulent Separation Control Workshop, http://cfdval2004.larc.nasa.gov/case3.html, conducted by NASA for the flow over a wall-mounted hump. The flow over a hump is an example of a turbulent separated flow. This flow is characterized by a simple geometry, but, nevertheless, is rich in many complex flow phenomena such as shear layer instability, separation, reattachment, and vortex interactions. The baseline case has been successfully simulated by Gan et al., 2007. The flow is simulated at a Reynolds number of 371,600, based on the hump chord length, C, and Mach number of 0.04. The flow control is being achieved via a slot at approximately 65% C by using steady suction. Solutions are presented for the three-dimensional RANS SST, steady and unsteady, turbulence model and DES and LES turbulence modeling approaches. Multiple turbulence modeling approaches help to ascertain what techniques are most appropriate for capturing the physics of this complex separated flow. Second-order accurate time derivatives are used for all implicit unsteady simulation cases. Mean-velocity contours and turbulent kinetic energy contours are examined at different streamwise locations. Detailed comparisons are made of mean and turbulence statistics such as the pressure coefficient, skinfriction coefficient, and Reynolds stress profiles, with experimental results. The location of the reattachment behind the hump is compared with experimental results. The successful control of this turbulent separated flow causes a reduction in the reattachment length, compared with the uncontrolled case. The effects of steady suction on flow separation and reattachment are discussed.

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