The development of passive flow control vortices

Surface flow visualisation and Particle Image Velocimetry (PIV) were used to investigate the flow-field of sub-boundary layer vane vortex generators (VVGs) and steady jet vortex generators (SJVGs) in a separated flow at 20m/s. The vortex generators were mounted on a 2D bump which was situated on the floor of a 350mm by 250mm wind tunnel and had a separation zone on its trailing edge.Surface flow visualisation was used to select VVG spacings and SJVG velocity ratios for effective separation control and investigate surface flow. Instantaneous and mean parameters downstream of the VVG and SJVG were measured non-intrusively using PIV. The instantaneous behaviour of the vortices was assessed using the coherence of a vortex and fluctuations in the location of instantaneous peak vorticity. Coherence is a parameter that was developed in the course of this research and had not been encountered in the literature at the time experiments ceased. The mean behaviour of the vortices was assessed using traditional variables, such as, mean, peak vorticity and its location, diameter and circulation of the vortex. A flat plate VVG study was performed to allow direct comparisons with previous work to be made.It was found that vortices generated by both VVGs and SJVGs were unsteady irrespective of geometry, became incoherent with downstream distance and had an exponential decay in mean peak vorticity. Surface flow visualisation indicated that for multiple VVG configurations the co-rotating configuration with a spacing of 3h effectively minimised separation on the 2D bump. For SJVGs, a velocity ratio of 1.0 was sufficient for separation contro

Passive laminar flow control of crossflow vorticity

A passive laminar flow crossflow vorticity control system includes an aerodynamic or hydrodynamic surface having geometric perturbations. The perturbations include peaks and valleys having a predetermined spacing and aligned approximately in a streamline direction to force the formation of crossflow vortices. This minimizes amplification and growth of the vortices, thus delaying transition to turbulence and reducing overall drag

Recent advances in numerical simulation and control of asymmetric flows around slender bodies

The problems of asymmetric flow around slender bodies and its control are formulated using the unsteady, compressible, thin-layer or full Navier-Stokes equations which are solved using an implicit, flux-difference splitting, finite-volume scheme. The problem is numerically simulated for both locally-conical and three-dimensional flows. The numerical applications include studies of the effects of relative incidence, Mach number and Reynolds number on the flow asymmetry. For the control of flow asymmetry, the numerical simulation cover passive and active control methods. For the passive control, the effectiveness of vertical fins placed in the leeward plane of geometric symmetry and side strakes with different orientations is studied. For the active control, the effectiveness of normal and tangential flow injection and surface heating and a combination of these methods is studied

A numerical study of transition control by periodic suction-blowing

The applicability of active control of transition by periodic suction-blowing is investigated via direct numerical simulations of the Navier-Stokes equations. The time-evolution of finite-amplitude disturbances in plane channel flow is compared in detail with and without control. The analysis indicates that, for relatively small three dimensional amplitudes, a two dimensional control effectively reduces disturbance growth rates even for linearly unstable Reynolds numbers. After the flow goes through secondary instability, three dimensional control seems necessary to stabilize the flow. An investigation of the temperature field suggests that passive temperature contamination is operative to reflect the flow dynamics during transition

PENGARUH PENGGUNAAN NIFEDIPIN PADA PENDERITA HIPERTENSI TERHADAP LAJU ALIRAN SALIVA DAN PEMBESARAN GINGIVA

Background : The prevalence of hypertension is increasing in society. Nifedipine as one of antihypertensive drugs from Calcium Channel Blocker is the type of drug that is often used . The impact on the oral cavity due to the use of nifedipine in patients with hypertension can cause gingival enlargement and reduction in salivary flow . Aim : This research was to prove the influence of nifedipine on gingival enlargement and salivary flow. Method : This study is using observational analytic design with cross sectional approach. The required number of subjects in the study were 70 people who were divided into nifedipine-users group and control group. Subjects were conducted with consecutive sampling method. Gingival enlargement is measured vertically and horizontally using a periodontal probe. Saliva was conducted using passive drool for 1 minute. Result : Mann Whitney test can be concluded that there is a significant difference for gingival enlargement and salivary flow rate between nifedipine user groups and the control group ( p < 0,05 ). Conclusion : There is a significant relationship to gingival enlargement and salivary flow rate per minute between hypertensive patients who use nifedipine and do not use nifedipine. Keywords : Hypertension, nifedipine, salivary flow rate, gingival enlargeme

Biomimetic bluff body drag reduction by self-adaptive porous flaps

The performances of an original passive control system based on a biomimetic approach are assessed by investigating the flow over a bluff-body. This control device consists in a couple of flaps made from the combination of a rigid plastic skeleton coated with a porous fabric mimicking the shaft and the vane of the bird's feathers, respectively. The sides of a square cylinder have been fitted with this system so as to enable the flaps to freely rotate around their leading edge. This feature allows the movable flaps to self-adapt to the flow conditions. Comparing both the uncontrolled and the controlled flow, a significant drag reduction (up to 22%) has been obtained over a broad range of Reynolds number. The investigation of the mean flow reveals a noticeable modification of the flow topology at large scale in the vicinity of the controlled cylinder accounting for the increase of the pressure base in comparison with the natural flow. Meanwhile, the study of the relative motion of both flaps points out that their dynamics is sensitive to the Reynolds number. Furthermore, the comparative study of the flow dynamics at large scale suggest a lock-in coupling of the flap motion and the vortex shedding.Comment: 19 pages, 17 figures, submitted to Comptes-Rendus de l' Acad\'emie des Sciences (M\'ecanique

Variable-area nozzle automatically controls fluid flow

Simple, passive nozzle requires no active control system to vary injection area. Injection area changes with changing pressure, thereby allowing greater flow as pressure increases. As pressure drop across nozzle is decreased, spring action of segments causes them to move inward, decreasing the flow area

Chance-Constrained ADMM Approach for Decentralized Control of Distributed Energy Resources

Distribution systems are undergoing a dramatic transition from a passive circuit that routinely disseminates electric power among downstream nodes to the system with distributed energy resources. The distributed energy resources come in a variety of technologies and typically include photovoltaic (PV) arrays, thermostatically controlled loads, energy storage units. Often these resources are interfaced with the system via inverters that can adjust active and reactive power injections, thus supporting the operational performance of the system. This paper designs a control policy for such inverters using the local power flow measurements. The control actuates active and reactive power injections of the inverter-based distributed energy resources. This strategy is then incorporated into a chance-constrained, decentralized optimal power flow formulation to maintain voltage levels and power flows within their limits and to mitigate the volatility of (PV) resources