Numerical investigation of double sided plasma vortex generator in separation control

Flow separation control over a wall-mounted hump model was studied experimentally to assess the performance of sweeping jet actuators. Results were compared to that of the 2004 CFD validation experiment (CFDVAL2004), which examined flow separation control with steady suction and unsteady zero-net-mass-flow actuators. Comparisons were carried out at low and high amplitude excitations. In addition to the active flow control methods, a passive flow control method (i.e., vortex generator) was used to complement the dataset. Steady/unsteady surface pressure measurements and surface oilflow visualization were used in the performance assessment of the actuators. The results indicated that the sweeping jet actuators are more effective than the steady suction and unsteady zero-net-mass-flow actuators. For the same momentum coefficient, the sweeping jet actuators produced more flow acceleration upstream of separation, more pressure recovery downstream, and consistently a smaller separation bubble.

The method of reducing automotive intake noise can be classified by passive and active control techniques. However, passive control has a limited effect of noise reduction at low frequency range (below 500 Hz) and is limited by the space of the engine room. However, active control can overcome these passive control limitations. The active control technique mostly uses the Least-Mean-Square (LMS) algorithm, because the LMS algorithm can easily obtain the complex transfer function in real-time, particularly when the Filtered-X LMS (FXLMS) algorithm is applied to an active noise control (ANC) system. However, the convergence performance of the LMS algorithm decreases significantly when the FXLMS algorithm is applied to the active control of intake noise under rapidly accelerating driving conditions. Therefore, in this study, the Co-FXLMS algorithm was proposed to improve the control performance of the FXLMS algorithm during rapid acceleration. The Co-FXLMS algorithm is realized by using an estimate of the cross correlation between the adaptation error and the filtered input signal to control the step size. The performance of the Co-FXLMS algorithm is presented in comparison with that of the FXLMS algorithm. Experimental results show that active noise control using Co-FXLMS is effective in reducing automotive intake noise during rapid acceleration.

Chapter 6 - Active control of thermoacoustic instability

Passive vortex generators (VG) are known as one of the ways to improve the flow of the wings and other surfaces in the presence of flow separation. In particular, the VG are installed on the wings and nacelles of many foreign airplanes, including the most recent ones (for example, Boeing 787, Airbus A-350). The principle of the passive VG effects on flow is to transfer the kinetic energy of the external flow separation region by the vortices system arising from the flow VG themselves. For example, by increasing the angle of attack of the wing separation it is highly three-dimensional picture of the flow and sufficiently sensitive to external influences. Thus separated flow can be controlled when using the VG destroy large separation vortices. The VG effectiveness depends on many parameters. This is primarily the relative position of the second harmonic and the separation region on the wing and their size and position relative to each other, the orientation of the second harmonic relative to the local flow direction of the external flow, etc. Obviously, the VG effect will depend essentially on the intensity ratio of the second harmonic vortexes and nature of flow separation in the separation area. In the presence of intense flow separation the effect of conventional VG may be reduced or not occur at all. Until recently, investigations and selection of position of conventional VG were made only experimentally. Currently, the possibilities of calculation methods allow estimating the VG effect on the flow in the separation area. However, due to the phenomenon complexity the accuracy of these calculations is low. The experimental data are required to validate the computational methods, including information not only about the total impact, but also about the flow structure in the separation area. To obtain such information is the subject of this paper. In the test model of high-lift devices swept wing with modern supercritical profile the parametric studies were performed on the VG effects on the flow in the intensive separation zone on flaps. A number of VG types is considered that differ by configuration, size, location in relation to the area of flow separation on the flap, as well as the orientation relative to the incoming flow. The major part of standard of VG positions is investigated. The VG influence on head velocity loss and the characteristics of the amplitude-frequency spectra of pressure fluctuations in the wake of the wing are obtained, as well as the flow spectra are obtained by means of fluorescent mini-tufts.

The combined effects of passive and active control on the vibration control of a com posite laminated plate with piezoelectric sensors/actuators are investigated. Finite element formula tion and modal analysis are presented. Classical laminated plate theory with the induced strain ac tuation and Hamilton's principle are used to formulate the equation of motion of the system. The total charge developed on the sensor layer is calculated from the direct piezoelectric equation. The equa tions of motion and the total charge are discretized with 4-node, 12-degree of freedom quadrilateral plate bending elements. The stiffness and damping property changes of composite structures by varying the layer angles are used as a passive control method. Piezoelectric sensors/actuators with negative velocity feedback control are used as an active control method. By numerical simulation, the effects of stiffness and damping property changes of composite structures and the effects of sen sor/actuator division on the response of the structure and the performance of the vibration control are investigated. Since active control and passive control affect each other, the active control and the passive control should be considered simultaneously in designing the efficient adaptive structures.

In this paper, an application is considered of both active and passive controls, to suppression of chaotic behavior of a simple portal frame, under the excitation of an unbalanced DC motor, with limited power supply (non-ideal problem). The adopted active control strategy consists of two controls: the nonlinear (feedforward) in order to keep the controlled system in a desirable orbit, and the feedback control, which may be obtained by considering state-dependent Riccati equation control to bringing the system into the desired orbit using a magneto rheological (MR) damper. To control the electric current applied in control of the MR damper the Bouc-Wen mathematical model was used to the MR damper. The passive control was obtained by means of a nonlinear sub-structure with properties of nonlinear energy sink. Simulations showed the efficiency of both the passive control (energy pumping) and active control strategies in the suppression of the chaotic behavior.

The opportunity for the reattachment and control of separated flows occurs in inlets, compressors, transition ducts and turbines. Passive and active control of separated flows has been demonstrated successfully by a number of techniques which employ the introduction of longitudinal or streamwise vortices. The role of these vortices is initially to reenergize the wall boundary layer flow by entraining and redistributing momentum from the primary flow to the wall layer and enhance early transition. A chain of non-linear interactions of these unsteady vortices with large scale unsteady separation vortices and the shed shear layer results in significant alteration of the circulation. The resulting increased circulation allows higher blade loadings, reduced part count, as well as increased performance at low Reynolds numbers. Flow control location has been investigated at chord locations ahead, at, and after separation. Passive dimples with single and multiple rows, varied dimple location and dimple shape have been investigated. Initial investigations of a single row of dimples and their wakes on a high pressure turbine vane ring have been performed at Reynolds numbers down to 13,500 in a full scale matched parameter rig. Properly placed dimples reattach separated flows at all Reynolds numbers investigated. Computations for the dimple geometries with VBI, MISES, and Fluent have been carried out to determine initial separation, compressible implications, reattachment locations, and predicted wake profiles or loss coefficients. Steady and pulsed vortex generator jets with duty cycles down to 1%, have both demonstrated reattachment and reduction of total losses in excess of 40% at Reynolds numbers down to 25,000, without incurring significant additional losses at higher Reynolds numbers. Pulsed vortex generator jets with a duty cycle of 1% have demonstrated blowing coefficients of <10 -4 .

In this paper we provide a review of the state of the art for active vibration control of axially moving materials (string and beam, etc.) in the past ten years, with particular regard to the subjects of some important active control methods of axially moving strings. First, an introduction is given to explain the aims and scope of this paper. This is followed by a comprehensive discussion of the active wave control methods presented by many investigators in the past ten years, including feedback control methods (such as the modal control method, the direct velocity feedback control method and the control method via transfer function formulation), active wave control methods combining transfer function, boundary control methods using the Lyapunov function, the variable structure control method, the adaptive control method, the vibration control of an axially moving beam and the active control of a moving material with arbitrarily varying length, etc. Finally, we conclude with a discussion of several issues for future research in this area.

The hydrodynamic behaviour of biologically inspired bristled shark skin vortex generator in submarine

Vortex generators (VG) are passive flow control devices used for avoiding or delaying the separation of the boundary layer by bringing momentum from the higher layers of the fluid towards the surface. The Vortex generator usually has the same height as the local boundary layer thickness, and these Vortex generators can produce overload drag in some cases. The aim of the present study was to analyze the characteristics and path of the primary vortex produced by a single rectangular vortex generator on a flat plate for the incident angles of β = 10 ∘ , 15 ∘ , 18 ∘ and 20 ∘ . A parametric study of the induced vortex was performed for six VG heights using Reynolds average Navier–Stokes equations at Reynodls number R e = 27,000 based on the local boundary layer thickness, using computational fluid dynamics techniques with OpenFOAM open-source code. In order to determine the vortex size, the so-called half-life radius was computed and compared with experimental data. The results showed a similar trend for all the studied vortex generator heights and incident angles with small variations for the vertical and the lateral paths. Additionally, 0.4H and 0.6H VG heights at incident angles of β = 18 ∘ and β = 20 ∘ showed the best performance in terms of vortex strength and generation of wall shear stress.

Vortex generator(VG) is one of the most successful flow control devices. A conventional VG is a passive control device; it does not adapt various velocity conditions. As an alternative to the conventional VG, we propose to use a plasma actuator(PA) as a VG. Since few studies have been made on such a vortex generator-type plasma actuator(VG-PA), many questions still remain open, e.g. , the mechanism of vortex generation and the magnitude of generated vortex. In the present study, we experimentally characterize and evaluate a VG-PA and examine the effect of burst mode. We also apply this VG-PA for suppression of vortex shedding from a panhead of used for high-speed trains. The present experiment shows that a VG-PA generates a distinct vortex and that flow separation around a panhead can be delayed by using VG-PA. It is also shown that a VG-PA operated in the burst mode works differently as compared to that in the continuous mode.

With a view to finding the best approach to maximize the wind energy harvesting from wind turbines, this research has focused towards assessing the effects of different innovative modifications to wind turbines at different wind speed conditions and comparing them in terms of aerodynamic performance, economy, and environmental impact. This study illustrates strategies like, active and passive flow control, incorporation of power augmentation devices (PADs) and biomimetic approaches, have huge potential to increase the output power of both the horizontal‐axis wind turbine (HAWT) and vertical‐axis wind turbine (VAWT). Literature survey reveals that boundary layer suction method from active flow control, diffusers as PADs and inspiration from flapping flight of insects from biomimetic approach can enhance the power coefficients of the turbine by 18.08%, 96%, and 35%, respectively. Furthermore, capacity factor (CF) and economic analysis showed that turbine modifications providing high‐CFs and low cost of energy (COE) will have priorities over the others, while selecting suitable turbines in a particular region. Moreover, it is evident that combining the best modifications for each strategy (active control, passive control, PADs, and biomimetic approaches) can lead to the maximum improvement in the overall performance of the turbines in terms of energy and economy.

Motor vehicle driver injury severity study under various traffic control at highway-rail grade crossings in the United States

The acoustic impedance at the diaphragm of an electroacoustic transducer can be varied using a range of basic electrical control strategies, amongst which are electrical shunt circuits. These passive shunt techniques are compared to active acoustic feedback techniques for controlling the acoustic impedance of an electroacoustic transducer. The formulation of feedback-based acoustic impedance control reveals formal analogies with shunt strategies, and highlights an original method for synthesizing electric networks ("shunts") with positive or negative components, bridging the gap between passive and active acoustic impedance control. This paper describes the theory unifying all these passive and active acoustic impedance control strategies, introducing the concept of electroacoustic absorbers. The equivalence between shunts and active control is first formalized through the introduction of a one-degree-of-freedom acoustic resonator accounting for both electric shunts and acoustic feedbacks. Conversely, electric networks mimicking the performances of active feedback techniques are introduced, identifying shunts with active impedance control. Simulated acoustic performances are presented, with an emphasis on formal analogies between the different control techniques. Examples of electric shunts are proposed for active sound absorption. Experimental assessments are then presented, and the paper concludes with a general discussion on the concept and potential improvements.

In this study, passive and active flow control methods were used together to manipulate the flow around a circular cylinder. The experiments were conducted in a wind tunnel for the Reynolds number range of 4000 and 10000 based on the diameter of the circular cylinder (D). A splitter plate was used as passive flow control device and its length was chosen to be about 3.75D. Plasma actuators were placed on the circular cylinder at a position of ±90° as an active flow control device. Combining the active and passive flow control methods, a greater reduction of the drag coefficient was achieved compared to that of the cases when using these methods separately. For Reynolds numbers of 5000 and 10000, the hybrid method gives a reduction in drag of 48% and 45%, respectively. The velocity measurements were carried out by using the hot-wire anemometry and velocity profiles were obtained in the wake region. The flow was visualized by using a smoke wire method. The results revealed that the wake region of the circular cylinder with plasma actuator and splitter plate has a narrower width than the plain cylinder and with splitter plate. Also, it can be seen from spectral analysis that the vortex shedding frequency was suppressed significantly by usage of the hybrid flow control method was used.