scholarly journals Investigation of the Normal Blowing Approach to Controlling Wingtip Vortex Using LES

2021 ◽  
Vol 2021 ◽  
pp. 1-15
Author(s):  
Yubiao Jiang ◽  
Wanbo Wang ◽  
Chen Qin ◽  
Patrick N. Okolo ◽  
Kun Tang
Keyword(s):  
Vortex Breakdown ◽  
Lower Surface ◽  
Chord Length ◽  
Primary Vortex ◽  
Momentum Coefficient ◽  
Wingtip Vortex ◽  
Before And After ◽  
Pressure Peak ◽  
Layer Flow ◽  
Induced Velocity

The characteristics and control of a wingtip vortex are of great significance when considering drag reduction and flight safety of transportation aircrafts. The associated aerodynamic phenomenon resulting from rolling up of a wingtip vortex includes boundary layer flow, shear layer separation, and vortex breakdown, while the interaction of a wingtip vortex with the airframe causes induced drag, wingtip noise, etc. This paper studies a normal blowing method utilized to control the wingtip vortex. Large eddy simulation (LES) technique applied to a straight NACA0012 wing having a chord length ( c ) of 0.4 m is adopted for this study. The Reynolds number based on the chord length is 1.6 × 10 6 and the angle of attack is 12°. The computational approach utilized the dynamic Smagorinsky-Lilly subgrid model for 3D simulations. Normal blowing from a high aspect ratio jet from the wingtip lower surface was used to control the wingtip vortex. From 0.05c to 0.30c, the blowing slit width was 1 mm, with the slit exit treated as a velocity inlet boundary condition which supplied the blowing jet with a momentum coefficient of 0.28%. Results of axial velocity and span-wise pressure distribution of the clean airfoil presented good agreement with known experimental data. LES results indicate that normal blowing suppresses the primary vortex strength, while the vortex core radius, maximum induced velocity, axial vorticity flux, and pressure peak of the primary vortex are reduced by 25%, 28%, 46%, and 52%, respectively. Flow field structures before and after blowing show that blowing suppresses the shedding, coiling, and convergence of the free vortex layers near the primary vortex. This study also shows that normal blowing generates a jet-induced vortex at the location of the secondary vortex, while backflow, volume expansion, and spiral burst can be observed in the jet-induced vortex. The bursting jet-induced vortex destroys the jet-like flow structure of the primary vortex at the trailing edge.

Changes in the behaviour ofOcypode quadrata(Fabricius, 1787) after experimental trampling

2018 ◽  
Vol 99 (5) ◽  
pp. 1135-1140 ◽  
Author(s):  
Leonardo Lopes Costa ◽  
Julyana Figueiredo Madureira ◽  
Ilana Rosental Zalmon
Keyword(s):  
Surface Activity ◽  
Sampling Design ◽  
Lower Surface ◽  
Sandy Beaches ◽  
Controlled Experiment ◽  
Visitation Rates ◽  
Ghost Crabs ◽  
Before And After

AbstractThe effects of trampling are usually confounded by the diffuse impacts of the urbanization of sandy beaches. We performed a controlled experiment on a beach with low visitation rates to test the hypothesis that ghost crabs avoid building their burrows on impacted plots as a result of the compacted sediment, and they migrate to non-trampled areas. The sampling design encompassed 11 survey quadrats (6 × 6 m) above the strandline, including five trampled plots (100, 300, 900, 1500 and 3000 steps) and six non-trampled plots. The plots were sampled before and after 24, 48 and 72 h of experimental trampling. We found that the ghost crabs avoided building their burrows in only the 1500× and 3000× trampled plots after 24 h, but the avoidance was not related to sediment compactness. Additionally, the emersion time and escape distance from humans were significantly delayed in the most trampled plots, suggesting a lower surface activity and an avoidance of irregular (i.e. high micro-relief) sediment surfaces by ghost crabs, which might reduce their ability to perceive potential predators.

Pulsating Flow in a Channel With a Backward-Facing Step

1997 ◽  
Vol 50 (11S) ◽  
pp. S232-S236
Author(s):  
Alvaro Valencia
Keyword(s):  
Vortex Breakdown ◽  
Separation Zone ◽  
Pulsating Flow ◽  
Steady Flows ◽  
Reattachment Length ◽  
Flow Conditions ◽  
Backward Facing Step ◽  
Primary Vortex ◽  
Inlet Flow ◽  
Inlet Velocity

The incompressible laminar flow in a channel with a backward-facing step is studied for steady cases and for pulsating inlet flow conditions. For steady flows, the influrnce of the inlet velocity profile, the height of the step, and the Reynolds number on the reattachment length is investigated. A parabolic entrance profile was used for pulsating flow. It was found with amplitude of oscillation of one by Re = 100 that the primary vortex breakdown through one pulsatile cycle and the wall shear stress in the separation zone varied markedly with pulsating inlet flow.

scholarly journals Convection in directionally solidifying alloys under inclined rotation

2000 ◽  
Vol 412 ◽  
pp. 93-123 ◽  
Author(s):  
C. A. CHUNG ◽  
FALIN CHEN
Keyword(s):  
Boundary Layer ◽  
Inclination Angle ◽  
Boundary Layer Flow ◽  
Fluid Layer ◽  
Longitudinal Mode ◽  
Point Of View ◽  
Induced Flow ◽  
Layer Flow ◽  
Parallel Shear Flow ◽  
Induced Velocity

In an experiment on binary alloys directionally solidifying from below, Sample & Hellawell (1984) showed that the plume convection can be successfully prohibited by rotating the cooling tank around an inclined axis. In the present paper we interpret their experimental observation by an analytical approach. Results show that there is a flow induced by the inclination. The induced flow in the fluid layer is a parallel shear flow consisting of three parts: the thermal boundary-layer flow, the solute boundary- layer flow, and the Ekman-layer flow. In the mush, the induced flow is also a parallel flow but of much smaller velocity, consisting of two flows of opposite directions. The induced velocity in the fluid layer increases with inclination angle and decreases with the effective Taylor number Te. The induced velocity in the mush also increases with inclination angle but remains virtually the same on varying the speed of rotation. The linear stability analysis of the mushy layer shows that, due mostly to the reduction of buoyancy, the mush becomes more stable as the inclination angle increases. In the precession-only case, the most-unstable mode of instability is the longitudinal mode, which propagates in a direction perpendicular to the induced flow. In the spin (with or without precession) case, the instability modes propagating in different directions are of equal stability. Because the induced flow changes direction with a frequency equal to the spin angular velocity, the flow scans over all the directions of the system and stabilizes equally the modes in different directions. We conclude on the basis of the present results and from the practical point of view that spin-only rotation is more effective than the precession-only rotation in stabilizing the convection during solidification.

Experimental Evaluation of Active Flow Control Mixed-Flow Turbine for Automotive Turbocharger Application

2005 ◽  
Author(s):  
Apostolos Pesiridis ◽  
Ricardo F. Martinez-Botas
Keyword(s):  
Flow Control ◽  
Pulse Pressure ◽  
Active Flow Control ◽  
Energy Levels ◽  
Expansion Ratio ◽  
Exhaust Gas ◽  
Potential Gain ◽  
Before And After ◽  
Pressure Peak ◽  
Active Flow

The current paper introduces a new concept in turbocharger development, namely, that of active turbocharger flow control. In the Active (Flow) Control Turbocharger (ACT) the nozzle is able to alter the inlet area at the throat of the turbine inlet casing in phase and at the same frequency as that of the incoming exhaust stream pulses. Actuated by an electrodynamic shaker the nozzle can adapt according to the engine exhaust gas pulse pressure variation, thus taking advantage of the lower energy levels existent before and after each pulse pressure peak, which the current systems do not take advantage of. Thus, ACT makes better use of the exhaust gas energy of the engine than a conventional VGT. The numerical simulation and experimental work concentrates on the potential gain in turbine expansion ratio and eventual power output as well as the corresponding effects on efficiency.

Transient Convective Heat Transfer for Laminar Boundary Layer Flow With Effects of Wall Capacitance and Resistance

1977 ◽  
Vol 99 (4) ◽  
pp. 513-519 ◽  
Author(s):  
R. C. C. Wang ◽  
B. T. F. Chung ◽  
L. C. Thomas
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Laminar Boundary Layer ◽  
Boundary Layer Flow ◽  
Nonlinear Partial Differential Equations ◽  
Lower Surface ◽  
Interface Temperature ◽  
Layer Flow

Transient forced convective heat transfer from a laminar boundary layer flow over a flat plate with appreciable thermal capacity and resistance is studied analytically. In the analysis, the flow is assumed to be steady and incompressible and the solid plate is subjected to a uniform step heat input at the lower surface. The integral method is utilized to reduce systems of nonlinear partial differential equations to a single integro-differential equation in terms of interfacial temperature which is then solved with the aid of finite difference technique. Numerical results for the fluid-solid interface temperature, heat transfer coefficient, and temperature distributions within the fluid and solid are presented. Some limiting solutions are found to agree well with the results of the previous theoretical analyses.

On the boundary flow using pulsed nanosecond DBD plasma actuators

2018 ◽  
Vol 32 (12n13) ◽  
pp. 1840035
Author(s):  
Zi-Jie Zhao ◽  
Y. D. Cui ◽  
Jiun-Ming Li ◽  
Jian-Guo Zheng ◽  
B. C. Khoo
Keyword(s):  
Flat Plate ◽  
Stable State ◽  
Single Pulse ◽  
Plasma Actuator ◽  
Plasma Actuators ◽  
Pulsed Plasma ◽  
Dbd Plasma ◽  
Narrow Region ◽  
Layer Flow ◽  
Induced Velocity

Our previous studies in quiescent air environment [Z. J. Zhao et al., AIAA J. 53(5) (2015) 1336; J. G. Zheng et al., Phys. Fluids 26(3) (2014) 036102] reveal experimentally and numerically that the shock wave generated by the nanosecond pulsed plasma is fundamentally a microblast wave. The shock-induced burst perturbations (overpressure and induced velocity) are found to be restricted to a very narrow region (about 1 mm) behind the shock front and last only for a few microseconds. These results indicate that the pulsed nanosecond dielectric barrier discharge (DBD) plasma actuator has stronger local effects in time and spatial domain. In this paper, we further investigate the effects of pulsed plasma on the boundary layer flow over a flat plate. The present investigation reveals that the nanosecond pulsed plasma actuator generates intense perturbations and tends to promote the laminar boundary over a flat plate to turbulent flow. The heat effect after the pulsed plasma discharge was observed in the external flow, lasting a few milliseconds for a single pulse and reaching a quasi-stable state for multi-pulses.

scholarly journals SPONTANEOUS DECREASE OF THE SURFACE TENSION OF SERUM. I

1922 ◽  
Vol 35 (4) ◽  
pp. 575-597 ◽  
Author(s):  
P. Lecomte du Noüy
Keyword(s):  
Surface Tension ◽  
Surface Layer ◽  
Lower Surface ◽  
Rapid Decrease ◽  
A Value ◽  
Characteristic Constant ◽  
Before And After ◽  
Ring Method ◽  
Lower Surface Tension ◽  
Prolonged Heat

1. Over 3,000 measurements of surface tension of sera have been made with the ring method, and they have yielded a new phenomenon, the spontaneous and rapid decrease of the surface tension of a serum in function of the time. 2. Generally, after 10 minutes the surface tension reaches a value which is practically constant. At least, the decrease is very much slower. After stirring, a rise occurs and a similar phenomenon takes place; but stability is not obtained as rapidly, requiring about 25 minutes. By stirring again, the same thing happens repeatedly, the slope of the curve being less marked each time, the rise in surface tension being slightly below each previous value, and the phenomenon undergoing a sort of damping. 3. An equation was established which expresses the experimental facts with an accuracy of about 0.2 per cent. It applies to the whole phenomenon, before and after stirring. It has only one characteristic constant, See PDF for Equation This formula, by simply changing t to c (concentration), expresses satisfactorily in general the phenomenon of adsorption in the surface layer; that is, the decrease in surface tension in function of the concentration. 4. Prolonged heat, at 55°C., and time seem to inhibit this phenomenon. 5. When precipitation occurs in a serum, the bottom of the liquid, which contains the precipitate, has the highest surface tension. When stirred, the surface tension rises a little every time. The upper part, clear, with lower surface tension, shows the reverse phenomenon; after every stirring, the surface tension becomes a little lower.

scholarly journals NADI SHODHANA PRANAYAMA AND ITS IMPACT ON PARAMETERS OF CARDIOVASCULAR, PULMONARY, AND BRAIN FUNCTIONS

2019 ◽  
Vol 3 (7) ◽  
Author(s):  
Dr. Shreyasi Vaksh ◽  
Dr. Mukesh Pandey
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Peak Expiratory Flow ◽  
Flow Rate ◽  
Peak Expiratory Flow Rate ◽  
Brain Functions ◽  
Before And After ◽  
Pressure Peak ◽  
Expiratory Flow ◽  
Underlying Mechanisms

Background: Practice of pranayama has been recognized to control cardiac autonomic status with an improvement in cardio-respiratory functions. Objective: To determine impact of Nadi-shodana pranayama practice for 20 minutes on heart rate, systolic and diastolic blood pressure, peak expiratory flow rate. Methods: Ninety normal healthy subjects aged between 17-20 years of first year MBBS course volunteered for this study out of total 150. Among them 40 were females and 50 were males. They did not have any previous training in Pranayama. All the selected physiological parameters were measured before and after performing ‘Nadi-shodhana Pranayama’. Epi-info 7 was used for analysis. Results: Following nadi-shodhana pranayama a significant decline in basal heart rate and systolic blood pressure was observed. Peak expiratory flow rate was significantly improved (P<0.01). No significant changes in respiratory and other cardiovascular parameters were seen. Conclusion: Nadi-shodhana Pranayama swiftly alters cardiopulmonary response. Further studies on a larger sample size need to illustrate the underlying mechanisms involved in this alteration. Keywords: Nadi-shodhana pranayama, heart rate, blood pressure, peak expiratory flow rate.

Hysteresis in swirling jets

1996 ◽  
Vol 309 ◽  
pp. 1-44 ◽  
Author(s):  
Vladimir Shtern ◽  
Fazle Hussain
Keyword(s):  
Stokes Equations ◽  
Vortex Breakdown ◽  
Reverse Flow ◽  
Axial Flow ◽  
Hysteresis Loops ◽  
Navier Stokes ◽  
Swirling Jets ◽  
Swirling Jet ◽  
Pressure Peak ◽  
Similar Solutions

This paper explains hysteretic transitions in swirling jets and models external flows of vortex suction devices. Toward this goal, the steady rotationally symmetric motion of a viscous incompressible fluid above an infinite conical stream surface of a half-angle θc is studied. The flows analysed are generalizations of Long's vortex. They correspond to the conically similar solutions of the Navier-Stokes equations and are characterized by circulation Γc given at the surface and axial flow force J1. Asymptotic analysis and numerical calculations show that four (for θc ≤ 90°) or five (for θc > 90°) solutions exist in some range of Γc and J1.The solution branches form hysteresis loops which are related to jump transitions between various flow regimes. Four kinds of jump are found: (i) vortex breakdown which transforms a near-axis jet into a two-cell flow with a reverse flow near the axis and an annular jet fanning out along conical surface θ = θs < θc (ii) vortex consolidation causing a reversal of (i); (iii) jump flow separation from surface θ = θc and (iv) jump attachment of the swirling jet to the surface. As Γc and/or J1 decrease, the hysteresis loops disappear through a cusp catastrophe. The physical reasons for the solution non-uniqueness are revealed and the results are discussed in the context of vortex breakdown theories. Vortex breakdown is viewed as a fold catastrophe. Two new striking effects are found: (i) there is a pressure peak of O(Γ2c) inside the annular swirling jet; and (ii) a consolidated swirling jet forms with a reversed (‘anti-rocket’) flow force.

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