Computational Study of a NACA4415 Airfoil Using Synthetic Jet Control

Computational Study of a NACA4415 Airfoil Using Synthetic Jet Control
Author: Omar Dario Lopez Mejia
Publisher:
Total Pages: 384
Release: 2009
Genre:
ISBN:

Synthetic jet actuators for flow control applications have been an active topic of experimental research since the 90's. Numerical simulations have become an important complement of that experimental work, providing detailed information of the dynamics of the controlled flow. This study is part of the AVOCET (Adaptive VOrticity Control Enabled flighT) project and is intended to provide computational support for the design and evaluation of closed-loop flow control with synthetic jet actuators for small scale Unmanned Aerial Vehicles (UAVs). The main objective is to analyze active flow control of a NACA4415 airfoil with tangential synthetic jets via computational modeling. A hybrid Reynolds-Averaged Navier-Stokes/Large Eddy Simulation (RANS/LES) turbulent model (called Delayed Detached-Eddy Simulation-DDES) was implemented in CDP, a kinetic energy conserving Computational Fluid Dynamics (CFD) code. CDP is a parallel unstructured grid incompressible flow solver, developed at the Center for Integrated Turbulence Simulations (CITS) at Stanford University. Two models of synthetic jet actuators have been developed and validated. The first is a detailed model in which the flow in and out of the actuator cavity is modeled. A second less costly model (RSSJ) was also developed in which the Reynolds stress produced by the actuator is modeled, based on information from the detailed model. Several static validation test cases at different angle of attack with modified NACA 4415 and Dragon Eye airfoils were performed. Numerical results show the effects of the actuators on the vortical structure of the flow, as well as on the aerodynamic properties. The main effect of the actuation on the time averaged vorticity field is a bending of the separation shear layer from the actuator toward the airfoil surface, resulting in changes in the aerodynamic properties. Full actuation of the suction side actuator reduces the pitching moment and increases the lift force, while the pressure side actuator increases the pitching moment and reduces the lift force. These observations are in agreement with experimental results. The effectiveness of the actuator is measured by the change in the aerodynamic properties of the airfoil in particular the lift ([Delta]C[subscript t]) and moment ([Delta]C[subscript m]) coefficients. Computational results for the actuator effectiveness show very good agreement with the experimental values (over the range of -2° to 10°). While the actuation modifies the global pressure distribution, the most pronounced effects are near the trailing edge in which a spike in the pressure coefficient (C[subscript p]) is observed. The local reduction of C[subscript p], for both the suction side and pressure side actuators, at x/c = 0.96 (the position of the actuators) is about 0.9 with respect to the unactuated case. This local reduction of the pressure is associated with the trapped vorticity and flow acceleration close to the trailing edge. The RSSJ model is designed to capture the synthetic jet time averaged behavior so that the high actuation frequencies are eliminated. This allows the time step to be increased by a factor of 5. This ad hoc model is also tested in dynamic simulations, in which its capacity to capture the detail model average performance was demonstrated. Finally, the RSSJ model was extended to a different airfoil profile (Dragon Eye) with good results.

Enhancing the Aerodynamic Performance of Stepped Airfoils

Enhancing the Aerodynamic Performance of Stepped Airfoils
Author: Ranganadhan Voona
Publisher:
Total Pages: 0
Release: 2012-10-26
Genre: Aerofoils
ISBN: 9783659266003

"The main objective of this research was to investigate the lift and drag characteristics of a stepped airfoil with backward facing steps; apply active flow control technique to enhance the aerodynamic performance of stepped airfoils and examine the possibility of using such airfoils on Unmanned Aerial Vehicles (UAV's). A step was introduced at mid-chord, with a depth of 50% of the airfoil thickness at mid-chord position extending till the trailing edge of a NACA 4415 airfoil. Computational studies were conducted with the use of passive flow control constituting the activation of step and active flow control with the use of air injecting jets placed in the step cavity of the NACA 4415 airfoil with a goal of enhancing the aerodynamic performance. The jet angle and jet momentum coefficient were varied independently to identify the best setting for optimizing the aerodynamic performance of the stepped airfoil. Experimental studies of a scaled wing model with the same airfoil were conducted in a wind tunnel for a range of Reynolds numbers to validate some of the numerical results obtained for the cases of base and stepped airfoils. The results produced show that as much as 37% increase in C1 and as much as 12% increase in L/D ratios over conventional airfoil values could be obtained using stepped airfoils and further enhancement could be made with the employment of jets placed in the step cavities. The case study conducted as a part of this research focuses on the UAV RQ-2 Pioneer employing a stepped airfoil configuration by comparing its aerodynamic characteristics with the conventional NACA 4415 airfoil originally used on this aircraft. The primary objective of the case study was to identify and outline a step schedule for the flight envelope of the UAV Pioneer using a stepped airfoil configuration while applying active flow control to obtain enhanced aerodynamic performance over conventional NACA 4415 airfoil originally used and hence improve the flight performance characteristics like Range and Endurance of the aircraft"--Abstract, p. iii

Study of the Boundary Layer Flow Control Using Synthetic Jets by Means of Spectro-consistent Discretizations

Study of the Boundary Layer Flow Control Using Synthetic Jets by Means of Spectro-consistent Discretizations
Author: David Duran Perez
Publisher:
Total Pages:
Release: 2017
Genre:
ISBN:

This report presents a study of the interaction of AFC (specifically, synthetic jets) with the laminar boundary layer of a NACA 0012 airfoil. First of all, in order to understand the phenomenology of Navier-Stokes equations, a spectro-consistent Computational Fluid Dynamics (CFD) code has been developed from scratch. By using a spectro-consistent discretization, the fundamental symmetry properties of the underlying differential operators are preserved. This code also helps to understand how the energy is transported from big to small scales. After solving a paradigmatic problem (TGV) using the aforementioned code, a mature CFD code (Alya) is used to simulate the flow around the NACA 0012 airfoil. Alya software also uses a spectro-consistent code but in Finite Element Method (FEM). Once the reference cases are solved for different angles of attack, a boundary condition representing an idealized synthetic jet is implemented. A systematic parametrization of the synthetic jet has been performed in order to assess the level of flow control in the boundary layer. Results demonstrate that, by selecting a correct combination of actuator frequency and momentum coefficient, the lift coefficient increases while the drag coefficient decreases producing a better lift-to-drag ratio. This aerodynamic improvement implies that a better circulation control is achieved, less noise is produced and less fuel consumption is required. It is also worth noting that, for high angles of attack, it is necessary to perform 3D flow simulations in order to capture the entire physics of the problem.

Enhancing the Aerodynamic Performance of Stepped Airfoils

Enhancing the Aerodynamic Performance of Stepped Airfoils
Author: Ranganadhan Voona
Publisher:
Total Pages: 0
Release: 2012
Genre: Aerofoils
ISBN:

"The main objective of this research was to investigate the lift and drag characteristics of a stepped airfoil with backward facing steps; apply active flow control technique to enhance the aerodynamic performance of stepped airfoils and examine the possibility of using such airfoils on Unmanned Aerial Vehicles (UAV's). A step was introduced at mid-chord, with a depth of 50% of the airfoil thickness at mid-chord position extending till the trailing edge of a NACA 4415 airfoil. Computational studies were conducted with the use of passive flow control constituting the activation of step and active flow control with the use of air injecting jets placed in the step cavity of the NACA 4415 airfoil with a goal of enhancing the aerodynamic performance. The jet angle and jet momentum coefficient were varied independently to identify the best setting for optimizing the aerodynamic performance of the stepped airfoil. Experimental studies of a scaled wing model with the same airfoil were conducted in a wind tunnel for a range of Reynolds numbers to validate some of the numerical results obtained for the cases of base and stepped airfoils. The results produced show that as much as 37% increase in C1 and as much as 12% increase in L/D ratios over conventional airfoil values could be obtained using stepped airfoils and further enhancement could be made with the employment of jets placed in the step cavities. The case study conducted as a part of this research focuses on the UAV RQ-2 Pioneer employing a stepped airfoil configuration by comparing its aerodynamic characteristics with the conventional NACA 4415 airfoil originally used on this aircraft. The primary objective of the case study was to identify and outline a step schedule for the flight envelope of the UAV Pioneer using a stepped airfoil configuration while applying active flow control to obtain enhanced aerodynamic performance over conventional NACA 4415 airfoil originally used and hence improve the flight performance characteristics like Range and Endurance of the aircraft"--Abstract, leaf iii

Synthetic Jet Flow Control of Two-dimensional NACA 65(1)-412 Airfoil Flow with Finite-Time Lyapunov Exponent Analysis of Lagrangian Coherent Structures

Synthetic Jet Flow Control of Two-dimensional NACA 65(1)-412 Airfoil Flow with Finite-Time Lyapunov Exponent Analysis of Lagrangian Coherent Structures
Author:
Publisher:
Total Pages: 46
Release: 2016
Genre: Electronic books
ISBN:

Synthetic jet (SJ) control of a low-Reynolds number, unsteady, compressible, viscous flow over a NACA 65-(1)412 airfoil, typical for unmanned air vehicles and gas turbines, has been investigated computationally. A particular focus was placed in the development and control of Lagrangian Coherent Structures (LCS) and the associated Finite-Time Lyapunov Exponent (FTLE) fields. The FTLE fields quantitatively measure of the repulsion rate in forward-time and the attraction rate in backward-time, and provide a unique perspective on effective flow control. A Discontinuous-Galerkin (DG) methods, high-fidelity Navier-Stokes solver performs direct numerical simulation (DNS) of the airfoil flow. Three SJ control strategies have been investigated: immediately downstream of flow separation, normal to the separated shear layer; near the leading edge, normal to the airfoil suction side; near the trailing edge, normal to the airfoil pressure side. A finite difference algorithm computes the FTLE from DNS velocity data. A baseline flow without SJ control is compared to SJ actuated flows. The baseline flow forms a regular, time-periodic, asymmetric von Karman vortex street in the wake. The SJ downstream of flow separation increases recirculation region vorticity and reduces the effective angle of attack. This decreases the time-averaged lift by 2:98% and increases the time-averaged drag by 5:21%. The leading edge SJ produces small vortices that deflect the shear layer downwards, and decreases the effective angle of attack. This reduces the time-averaged lift by 1:80%, and the time-averaged drag by 1:84%. The trailing edge SJ produces perturbations that add to pressure side vortices without affecting global flow characteristics. The time-averaged lift decreases by 0:47%, and the time-averaged drag increases by 0:20%. For all SJ cases, the aerodynamic performance is much more dependent on changes to the pressure distribution than changes to the skin friction distribution. No proposed SJ case improved aerodynamic performance. Some desirable SJ control effects were observed, which may be isolated in a future study by optimizing SJ parameters. Stably increasing recirculation region vorticity, and maintaining or increasing the effective angle of attack are desirable for lift increase, while deflecting the separated shear layer downward is desirable for drag reduction.

Computational Analysis of Circulation Control Airfoils

Computational Analysis of Circulation Control Airfoils
Author:
Publisher:
Total Pages:
Release: 2004
Genre:
ISBN:

Current projections for future aircraft concepts call for stringent requirements on high-lift and low cruise-drag. The purpose of this study is to examine the use of circulation control, through trailing edge blowing, to meet both requirements. This study was conducted in two stages: (i) validation of computational fluid dynamic procedures on a general aviation circulation control airfoil and (ii) a study of an adaptive circulation control airfoil for controlling lift coefficients in the low-drag range. In an effort to validate computational fluid dynamics procedures for calculating flows around circulation control airfoils, the commercial flow solver FLUENT was utilized to study the flow around a general aviation circulation control airfoil. The results were compared to experimental and computational fluid dynamics results conducted at the NASA Langley Research Center. This effort was conducted in three stages: (i) a comparison of the results for free-air conditions to those from previously conducted experiments, (ii) a study of wind-tunnel wall effects, and (iii) a study of the stagnation-point behavior. In general, the trends in the results from the current work agreed well with those from experiments, some differences in magnitude were present between computations and experiments. For the cases examined, FLUENT computations showed no noticeable effect on the results due to the presence of wind-tunnel walls. The study also showed that the leading-edge stagnation point moves in a systematic manner with changes to the jet blowing coefficient and angle of attack, indicating that this location can be sensed for use in closed-loop control of such airfoil flows. The focus of the second part of the study was to examine the use of adaptive circulation control on a natural laminar flow airfoil for controlling the lift coefficient of the low-drag range. In this effort, adaptive circulation control was achieved through blowing over a small mechanical flap that can be deflec.

Experimental and Computational Investigation of Lift-Enhancing Tabs on a Multi-Element Airfoil

Experimental and Computational Investigation of Lift-Enhancing Tabs on a Multi-Element Airfoil
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
Total Pages: 158
Release: 2018-07-17
Genre:
ISBN: 9781723047541

An experimental and computational investigation of the effect of lift-enhancing tabs on a two-element airfoil has been conducted. The objective of the study was to develop an understanding of the flow physics associated with lift-enhancing tabs on a multi-element airfoil. An NACA 63(2)-215 ModB airfoil with a 30% chord fowler flap was tested in the NASA Ames 7- by 10-Foot Wind Tunnel. Lift-enhancing tabs of various heights were tested on both the main element and the flap for a variety of flap riggings. A combination of tabs located at the main element and flap trailing edges increased the airfoil lift coefficient by 11% relative to the highest lift coefficient achieved by any baseline configuration at an angle of attack of 0 deg, and C(sub 1max) was increased by 3%. Computations of the flow over the two-element airfoil were performed using the two-dimensional incompressible Navier-Stokes code INS2D-UP. The computed results predicted all of the trends observed in the experimental data quite well. In addition, a simple analytic model based on potential flow was developed to provide a more detailed understanding of how lift-enhancing tabs work. The tabs were modeled by a point vortex at the air-foil or flap trailing edge. Sensitivity relationships were derived which provide a mathematical basis for explaining the effects of lift-enhancing tabs on a multi-element airfoil. Results of the modeling effort indicate that the dominant effects of the tabs on the pressure distribution of each element of the airfoil can be captured with a potential flow model for cases with no flow separation. Ashby, Dale L. Ames Research Center LIFT; AIRFOILS; TABS (CONTROL SURFACES); WIND TUNNEL TESTS; ANGLE OF ATTACK; NAVIER-STOKES EQUATION; COMPUTATIONAL FLUID DYNAMICS; GRID GENERATION (MATHEMATICS); AIRFOIL PROFILES; FLAPS (CONTROL SURFACES); TRAILING EDGES; INCOMPRESSIBLE FLOW; DATA CORRELATION; PREDICTION ANALYSIS TECHNIQUES; VORTICES; POTENTIAL FLOW; PRESSURE DISTRIBUTION; AERODYNAMIC C...

Numerical Investigation of Flow Control Over an Airfoil

Numerical Investigation of Flow Control Over an Airfoil
Author: Eray AKÇAYÖZ
Publisher: LAP Lambert Academic Publishing
Total Pages: 88
Release: 2010-05
Genre:
ISBN: 9783838356013

The synthetic jet is applied over an airfoil to control the flow separation. Response Surface Methodology is employed for the optimization of synthetic jet parameters at various angles of attack. The synthetic jet parameters; the jet velocity, the jet location, the jet angle and the jet frequency are optimized to maximize the lift to drag ratio. The jet power coefficient is kept constant in the optimization. The lift to drag ratio increased significantly especially at post stall angles of attack.