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Control of Flow Separation over Naca 0015 Airfoil Using Synthetic Jet Actuators 2
| Content Provider | Semantic Scholar |
|---|---|
| Author | Azzawi, Itimad Dawood Jumaah Abed, Khuder N. |
| Copyright Year | 2016 |
| Abstract | In this paper the concept of active flow control using an array of synthetic jet actuators has been investigated. Synthetic jets are the one type of actuators that will be used in this research to introduce important modification to the pressure distribution levels that appear over the lifting surface of airfoil model when the flow separation exists. Two synthetic jet actuators arrays were used; the first one placed at 3% c and the second array located at 6% c on the upper surface of a NACA0015 airfoil. The experiments are conducted at Re=455000 in 8 different angles of attack 0o to 15o using the wind tunnel at University of Diyala. The first part of this paper concentrates on making comparison of the collected experimental data of the pressure distribution over NACA0015 airfoil at Re = 4.4x10 at angle of attack varied from 0.0 to 20 degrees without synthetic jet actuators (baseline case study) and previous experimental results as a baseline validation of the onset of flow separation location. Figure 3 and 4 clearly showed that the pressure distribution and the calculated lift were converged in the stall region at high angle of attack. In the second part of this study we had utilized a NACA0015 airfoil of 300 mm chord length with a rounded leading edge of 20 mm diameter. 18 discrete synthetic jet actuators with 1.2 mm diameter is distributed along the lifting surface of the wing. This distribution is used to investigate the effect of jets and vertical structures on the characteristics of pressure coefficients (Cp) and flow separation over the airfoil. Pressure and lift coefficients have been measured and calculated by using surface pressure measurements technique that uses 29 pressure tapings over the lifting surface of the wing. A piezo-ceramic diaphragms technology of 15mm diameter have been used in the experiments and excited at a variety of frequencies (resonant frequency and vortex shedding separated flow frequency) in order to get the effective interaction between the synthetic jets and separated boundary layer which is the most significant parameter of producing the vertical structure that affects the flow separation. The results showed that at 3% c SJA location, the best enhancement in the lift was seen at Vp-p of 8 which increased by about 0.1. However, the overall results showed that maximum enhancement in lift of about 0.2 at 6% c. Keywords—Flow Separation Control, Synthetic Jet Actuators, Airfoils 1-INTRODUCTION: The performance of an airplane wing has a significant impact on the runway distance, approach speed, climb rate, payload capacity, and operation range. Since the beginning of human flight, many researchers and engineers have attempted to increase lift and reduce drag by changing aircraft structure or configuration. The performance of an airplane wing is often degraded by flow separation. Flow separation on an airfoil surface is related to the aerodynamic design of the airfoil profile. However, non-aerodynamic constraints such as material property, manufacturability, and stealth capability in military applications often Diyala Journal of Engineering Sciences Second Engineering Scientific Conference / College of Engineering-University of Diyala16-17 Dec. 2015 CONTROL OF FLOW SEPARATION OVER NACA 0015 AIRFOIL USING SYNTHETIC JET ACTUATORS Diyala Journal of Engineering Sciences, Vol. 08, No. 04, Special Issue 675 conflict with the aerodynamic constraints, and either passive or active flow control is required to overcome the difficulty [1]. Flow control over airfoil is primarily directed at increasing the lift and decreasing the drag produced by the airfoil. This is usually achieved by manipulating the boundary and shear layer flows in order to minimize the separation region over the suction surface of the airfoil. Active flow control refers to the process of the expending energy in order to modify the flow [2]. This is distinct from passive techniques where flow control is provided without expending energy through means such as vortex generators have proven to be effective in delaying flow separation under some conditions. Advantages of active flow control include the ability to attain a large effect using a small, localized energy input, and to control complex dynamical processes; for example, the reduction of skin friction and hence viscous drag [3, 4] in turbulent boundary layers. A synthetic jet actuator (SJA) is a jet generator that requires zero mass input yet produces non-zero momentum output. Developed in recent years, the synthetic jet actuator falls within the area of micro-electro-mechanical systems (MEMS) if the characteristic dimension or the diameter of the orifice, through which the jets are generated, is less than 1.0mm [3]. Advantages of using SJA include simple compact structure, low cost and ease of operation. The basic components of a SJA are a cavity and an oscillating material. A jet is synthesized by oscillatory flow in and out of the cavity via an orifice in one side of the cavity. The flow is induced by a vibrating membrane located on one wall of the cavity. There are many types of actuator that can be used in active flow control, such as thermal, acoustic, piezoelectric, electromagnetic and shape memory alloys. Here, a piezoelectric material is chosen to drive the oscillating diaphragm because of such desirable characteristics as such low power consumption, fast response, reliability, and low cost [5]. Flow enters and exits the cavity through the orifice by suction and blowing. On the intake stroke, fluid is drawn into the cavity from the area surrounding the orifice. During one cycle of oscillation, this fluid is expelled out of the cavity through the orifice as the membrane moves upwards. Due to flow separation, a shear layer is formed between the expelled fluid and the surrounding fluid. This layer of vorticity rolls up to form a vortex ring under its own momentum. By the time the diaphragm begins to move away from the orifice to pull fluid back into the cavity, the vortex ring is sufficiently distant from the orifice that it is virtually unaffected by the entrainment of fluid into the cavity. Thus, over a single period of oscillation of the diaphragm, whilst there is zero net mass flux into or out of the cavity, there is also a non-zero mean momentum flux flow control can be achieved using traditional devices such as steady [6] and pulsed [7] jets. The obvious benefit of employing SJAs as a flow control device is that they require no air supply and so there is no need for piping, connections, and compressors associated with steady jets. The focus of the present paper is to investigate the lift enhancement mechanism using synthetic jets on NACA0015 airfoil, which has been frequently used as a model airfoil of various high lift systems [8, 9, and 10]. Various synthetic jets were applied to NACA0015 with two locations of synthetic jet actuators arrays were used; the first one is placed at 3% c and the second array is located at 6% c on the lifting surface of a NACA0015 airfoil , and the flow characteristics of separation control on the leading edge were examined. Performance of the synthetic jet with a simple high-lift device under optimal flow control conditions was investigated. Furthermore, a multi-array synthetic jet was introduced as a way to reduce the amplitude of the jet peak velocity. And multi-location synthetic jets were also investigated as a remedy to cure unstable separated vortex flows on the airfoil suction surface. Finally, flow control combining multi-array and multi-location of synthetic jets was employed to provide a stable flow structure with a reduced jet peak velocity. 2. EXPERIMENTAL APPARATUS The flow behavior over an airfoil section model was investigated and then aerodynamic pressure coefficients were calculated with the help of the pressure distribution over Second Engineering Scientific Conference / College of Engineering-University of Diyala16-17 Dec. 2015 CONTROL OF FLOW SEPARATION OVER NACA 0015 AIRFOIL USING SYNTHETIC JET ACTUATORS Diyala Journal of Engineering Sciences, Vol. 08, No. 04, Special Issue 676 NACA0015 model mounted inside wind tunnel. The subsonic wind tunnel used in current research is an open circuit type with a working cross section of (300mm x 300mm) as schematically shown in Figure 1. All experiments were conducted at Re = 455000 in 6 different angles of attack 6o to 15o using the wind tunnel facility at college of engineering , University of Diyala. A maximum flow speed of 36 m/sec had allowed the experiments on many aspects of incompressible air flow of subsonic aerodynamics were performed at satisfactory Reynolds number. The tunnel has a smooth contraction fitted with protective mesh screen to increase the flow uniformity inside the test section with working section constructed of clear Perspex. A model of wood of the NACA 0015 airfoil has been built locally. The data for this section were taken from NACA’s lists of wings section [11, 12]. Moreover, its coordinate has been listed in Table 1.The wing section model specification has a cord (C=300mm) with a rounded leading edge of 20 mm diameter, the section length (b=300mm). A standard multi tubes manometer was used which consists of 30 manometers to measure the surface pressure distribution. The manometer connected with the stainless steel pressure tubes over the wing section model by a rubber snout. In this research, 29 pressure taps have been used on the upper and lower surface of the wing. Two synthetic jet actuators arrays were used: the first one was placed at 3% c with 9 discrete synthetic jet actuators which had 1.2 mm diameter and the second array was located at 6% c with 9 discrete synthetic jet actuators with 1.2 mm diameter on the upper surface of a NACA0015 airfoil as shown in Figure 2. The array of SJA was built at 3% of the chord length from the leading edge of the wing through nine holes with diameter of 16 mm and a depth of 2 mm in the flat plate m |
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| Alternate Webpage(s) | http://enginmag.uodiyala.edu.iq/uploads/Vol.%208,%20No.4%20Conference%202/Mechanics/5%20674-%20685.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
