Arvind Santhanakrishnan

Bio: Arvind Santhanakrishnan is an academic researcher from Oklahoma State University–Stillwater. The author has contributed to research in topics: Drag & Synthetic jet. The author has an hindex of 19, co-authored 63 publications receiving 993 citations. Previous affiliations of Arvind Santhanakrishnan include Emory University & University of Kentucky.

Flow control with plasma synthetic jet actuators

Abstract: This paper presents an experimental investigation of the characteristics of a plasma actuator design for flow control consisting of an annular electrode in quiescent and flat plate boundary layer flows. In quiescent flow, the circular plasma region produced on actuation was observed to generate a vertical zero-net mass flux (or synthetic) jet, hence the name plasma synthetic jet actuator, the characteristics of which were found to be affected by the actuator operation mode (steady or unsteady). Pulsed operation of the actuator results in the formation of a starting vortex ring that advects ahead of the jet and secondary vortex rings near the actuator surface due to the additional plasma-induced fluid entrainment in the boundary layer. By varying the actuator pulsing frequency, multiple vortex rings were created in the flowfield and the resulting vortex ring interactions were found to increase both the peak velocity and streamwise extent of the jet. The interaction of the actuator with a crossflow was observed to be similar to that seen in conventional or non zero-net mass flux jets with the plasma synthetic jet penetrating into the mean flow. As expected, the influence of the jet on the freestream was found to decrease with increasing mean velocity and the impact on displacement and momentum thickness values diminishes as well.

Clap and fling mechanism with interacting porous wings in tiny insect flight

Abstract: The aerodynamics of flapping flight for the smallest insects such as thrips is often characterized by a 'clap and fling' of the wings at the end of the upstroke and the beginning of the downstroke. These insects fly at Reynolds numbers (Re) of the order of 10 or less where viscous effects are significant. Although this wing motion is known to augment the lift generated during flight, the drag required to fling the wings apart at this scale is an order of magnitude larger than the corresponding force acting on a single wing. As the opposing forces acting normal to each wing nearly cancel during the fling, these large forces do not have a clear aerodynamic benefit. If flight efficiency is defined as the ratio of lift to drag, the clap and fling motion dramatically reduces efficiency relative to the case of wings that do not aerodynamically interact. In this paper, the effect of a bristled wing characteristic of many of these insects was investigated using computational fluid dynamics. We performed 2D numerical simulations using a porous version of the immersed boundary method. Given the computational complexity involved in modeling flow through exact descriptions of bristled wings, the wing was modeled as a homogeneous porous layer as a first approximation. High-speed video recordings of free-flying thrips in take-off flight were captured in the laboratory, and an analysis of the wing kinematics was performed. This information was used for the estimation of input parameters for the simulations. Compared with a solid wing (without bristles), the results of the study show that the porous nature of the wings contributes largely to drag reduction across the Re range explored. The aerodynamic efficiency, calculated as the ratio of lift to drag coefficients, was larger for some porosities when compared with solid wings.

Fluid Dynamics of Heart Development

Abstract: The morphology, muscle mechanics, fluid dynamics, conduction properties, and molecular biology of the developing embryonic heart have received much attention in recent years due to the importance of both fluid and elastic forces in shaping the heart as well as the striking relationship between the heart’s evolution and development. Although few studies have directly addressed the connection between fluid dynamics and heart development, a number of studies suggest that fluids may play a key role in morphogenic signaling. For example, fluid shear stress may trigger biochemical cascades within the endothelial cells of the developing heart that regulate chamber and valve morphogenesis. Myocardial activity generates forces on the intracardiac blood, creating pressure gradients across the cardiac wall. These pressures may also serve as epigenetic signals. In this article, the fluid dynamics of the early stages of heart development is reviewed. The relevant work in cardiac morphology, muscle mechanics, regulatory networks, and electrophysiology is also reviewed in the context of intracardial fluid dynamics.

Flow Control Using Plasma Actuators and Linear/Annular Plasma Synthetic Jet Actuators

Abstract: This paper investigates the use of dielectric barrier discharge plasma actuators in low Re flow control applications. Three different actuator geometries have been tested: a conventional design using two rectangular strip electrodes (the linear actuator) that produces a nearly two-dimensional horizontal wall jet upon actuation, and two new designs that render the plasma induced flow in the form of a vertical jet that can be either three-dimensional using an annular electrode array actuator construction the plasma synthetic jet actuator, PSJA or nearly two dimensional using a modified linear actuator construction consisting of two exposed electrodes and one embedded electrode, the L-PSJA. The modification in actuator design can be used to broaden its applicability and enhance the flow control effects. 2-D PIV measurements are used to characterize the operation of these actuators in quiescent flow, a flat plate boundary layer, and flow over a circular cylinder. In quiescent flow, these actuators add momentum to the residual fluid with significant velocity fluctuations. The interaction of the plasma induced flow with a mean flow is shown to vary with the actuator geometry. The PSJA and L-PSJA geometries enhance the penetration of the plasma induced jet as compared to the linear actuator. The actuators act as an active boundary layer trip, the effectiveness of which is seen to decrease with increasing freestream velocity. While the PSJA affects the global flowfield, the L-PSJA and linear actuator affect primarily the near wall region. The linear actuator is observed to be a better configuration for flow control on a circular cylinder as opposed to the L-PSJA.

On Plasma Synthetic Jet Actuators

Abstract: The term plasma actuator refers to an asymmetric arrangement of two electrodes (typically rectangular strips) separated by dielectric material that can be used as active flow control devices. A plasma actuator design consisting of an annular electrode array, the plasma synthetic jet actuator (PSJA), is experimentally investigated in this paper. This particular geometry creates a zero-net mass flux (or “synthetic”) jet upon actuation, and can be operated in a pulsed or steady manner for flow control or thrust generation. Unlike synthetic jets, the actuator configuration can be reversed to act as a suction device. 2-D PIV measurements are used to characterize the actuator mounted on a flat plate in quiescent flow. Pulsing the actuator results in formation of three counter-rotating vortex rings: a starting vortex ring that advects downstream ahead of the jet, a secondary vortex ring that is found to be “trapped” during the actuation phase, and a weak strength tertiary vortex ring created as a result of fluid entrainment in the boundary layer. Examination over a range of frequencies reveals varying values of peak jet velocity and momentum distribution based upon interactions of the starting vortices. The effects of changing pulsing frequency on the jet characteristics are discussed. Preliminary observations on a PSJA used for suction are also presented.

人唾液天疱疮抗原的纯化

Abstract: 1. Place animal in induction chamber and anesthetize the mouse and ensure sedation. 2. Once the animal is sedated, move it to a nose cone for hair removal using cream. Only apply cream to the area of the chest that will be utilized for imaging. Once the hair is removed, wipe area with wet gauze to ensure all hair is removed. 3. Move the animal to the imaging platform and tape its paws to the ECG lead plates and insert rectal probe. Body temperature should be maintained at 36-37°C. During imaging, reduce anesthesia to maintain proper heart rate. If the animal shows signs of being awake, use a higher concentration of anesthetic.

Airflow control by non-thermal plasma actuators

Abstract: Active flow control is a topic in full expansion due to associated industrial applications of huge importance, particularly for aeronautics. Among all flow control methods, such as the use of mechanical flaps, wall synthetic jets or MEMS, plasma-based devices are very promising. The main advantages of such systems are their robustness, simplicity, low power consumption and ability for real-time control at high frequency. This paper is a review of the worldwide works on this topic, from its origin to the present. It is divided into two main parts. The first one is dedicated to the recent knowledge concerning the electric wind induced by surface non-thermal plasma actuators, acting in air at atmospheric pressure. Typically, it can reach 8 m s−1 at a distance of 0.5 mm from the wall. In the second part, works concerning active airflow control by these plasma actuators are presented. Very efficient results have been obtained for low-velocity subsonic airflows (typically U∞ ≤ 30 m s−1 and Reynolds number of a few 105), and promising results at higher velocities indicate that plasma actuators could be used in aeronautics.

A Review of Morphing Aircraft

Abstract: Aircraft wings are a compromise that allows the aircraft to fly at a range of flight conditions, but the performance at each condition is sub-optimal. The ability of a wing surface to change its geometry during flight has interested researchers and designers over the years as this reduces the design compromises required. Morphing is the short form for metamorphose; however, there is neither an exact definition nor an agreement between the researchers about the type or the extent of the geometrical changes necessary to qualify an aircraft for the title ‘shape morphing.’ Geometrical parameters that can be affected by morphing solutions can be categorized into: planform alteration (span, sweep, and chord), out-of-plane transformation (twist, dihedral/gull, and span-wise bending), and airfoil adjustment (camber and thickness). Changing the wing shape or geometry is not new. Historically, morphing solutions always led to penalties in terms of cost, complexity, or weight, although in certain circumstances, thes...

Actuators for Active Flow Control

Abstract: Actuators are transducers that convert an electrical signal to a desired physical quantity. Active flow control actuators modify a flow by providing an electronically controllable disturbance. The field of active flow control has witnessed explosive growth in the variety of actuators, which is a testament to both the importance and challenges associated with actuator design. This review provides a framework for the discussion of actuator specifications, characteristics, selection, design, and classification for aeronautical applications. Actuator fundamentals are discussed, and various popular actuator types used in low-to-moderate speed flows are then described, including fluidic, moving object/surface, and plasma actuators. We attempt to highlight the strengths and inevitable drawbacks of each and highlight potential future research directions.