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WAKE HAZARD ALLEVIATION ASSOCIATED WITH ROLL OSCILLATIONS OF WAKE-GENERATING AIRCRAFT

JOURNAL OF AIRCRAFT 1986年第6期23卷 484-491页

作者： ROSSOW, VJ NASA Ames Research Center Moffett Field California

An explanation is provided for the difference in wake vortex alleviation achieved by roll oscillations during flight tests with B-747 and L-1011 transport aircraft. Both aircraft had their landing flaps extended and several spoilers deployed. Numerical analysis shows that the growth in amplitude of the initial waves in the vortex filaments is brought about by inviscid vortex interactions. In the case of the B-747, growth is enhanced by a vortex whose strength is about the same as the tip vortex that is shed near the fuselage by the inboard end of the flaps. Conversely, the L-1011 is estimated to shed a negligible fuselage vortex and to have a relatively strong wing tip vortex. These characteristics bring about a rotation and a large amplification of the initial waves in the vortex filaments in the wake of the B-747, but not in the L-1011 vortex wake. An aircraft following the B-747 would then experience only intermittent encounters with the intense parts of the wake vortices, such that the time-averaged wake-induced rolling moment is substantially reduced. © 1986 American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

关键词： Transport Aircraft Vortex Filaments Flight Testing Aircraft Configurations Wing Tip Numerical Analysis smoke flow visualization Lift Coefficient Wing Span Aerodynamic Force

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VORTEX-INDUCED BENDING OSCILLATION OF A SWEPT WING

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JOURNAL OF AIRCRAFT 1987年第3期24卷 195-202页

作者： ERICSSON, LE Lockheed Missiles & Space Company Inc. Sunnyvale California

An analysis of existing experimental results shows that the observed bending oscillations of a highly swept wing cannot have been caused by the induced effects of a single leading-edge vortex, but rather by the interaction between two leading-edge vortices, one generated by a thick inner wing or wing/body glove and the other by the outboard, thin, variable-sweep wing. This inner/outer wing vortex interaction is similar to that occurring on a double-delta planform wing. The cause of the negative aerodynamic damping from the vortex interaction is the sensitivity to the angle of attack and its time derivative of the spanwise location of a leadingedge vortex. © 1987 by L. E. Ericsson. Published by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

关键词： Delta Wing Vortex Mean Aerodynamic Chord Critical Angle of Attack Freestream Conditions smoke flow visualization Variable Sweep Wings Structural Damping Transonic Wind Tunnel Aerospace Industry Kinematic Viscosity

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Propeller Ground Effect in Forward Flight

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AIAA JOURNAL 2023年第10期61卷 4378-4390页

作者： Cai, Jielong Gunasekaran, Sidaard Univ Dayton Mech & Aerosp Dept Dayton OH 45469 USA

The study of the fixed-pitch small-scale propeller in-ground effect is extended to forward flight conditions at different incidence angles of the propeller. Force-based experiments, smoke flow visualization, surface flow visualization, and phase-locked particle image velocimetry (PIV) indicate the presence of three distinct performance zones as a function of the advance ratio and ground distance, where the ground effect changes drastically. The power required at constant thrust shows an increasing trend after a threshold advance ratio for each h/D and then decreases steeply upon a further increase in the advance ratio. Phase-locked PIV revealed the presence of a fountain vortex and a ground vortex at distinct J for each h/D distance that correlates with an increase in power and a decrease in thrust, respectively. At advance ratios below the onset of the fountain vortex lies the optimal ground effect zone. An increase in the advance ratio beyond this threshold will result in power increments due to the formation of the fountain vortex. A further increase in the advance ratio initiates the onset of the ground vortex where the ground effect is significantly reduced. The onset of the fountain vortex and the ground vortex occurs at comparatively lower advance ratios for propellers at a positive incidence angle. A normalization method is developed for ground effect forward flight that collapses the in-ground-effect performance for various normalized heights, advance ratios, and incidence angles.

关键词： Fixed Pitch Propellers smoke flow visualization Freestream Velocity Ground Effect (Aerodynamics) forward flight

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Moving-orientation and position effects of the piezoelectric fan on thermal characteristics of the heat sink partially filled in a channel with axial flow

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2015年 85卷 950-964页

作者： Jeng, Tzer-Ming Liu, Chi-Huang Chien Kuo Technol Univ Dept Mech Engn Changhua 500 Taiwan

This study experimentally investigated the heat transfer and fluid flow behaviors of the heat sink partially filled in a rectangular channel with the axial mainstream interacted by the oscillating movement of the upstream piezoelectric fan. Total eight heat sinks, including square pin-fin heat sinks (Models A-c), plate-fin heat sinks (Models D-F) and aluminum-foam heat sinks (Models G and H), were employed. The relevant parameters were the Reynolds number of the mainstream (Re), the oscillating-movement orientation of the piezoelectric fan and the location of the piezoelectric fan (the relative horizontal distance S/L = 0.25 and the relative vertical distance H-p/L = 0.22-0.62). The smoke flow visualizations demonstrate that the oscillating movement of the piezoelectric fan did strengthen the turbulent intensity of the mainstream at low Reynolds number, giving the additional disturbance momentum to the mainstream and making the fluid flow through the heat sink with turbulent flow characteristic. The heat transfer results indicate that the heat sink gained more heat transfer enhancement at smaller Re when the piezoelectric fan was operating. For example, when the piezoelectric fan was operating with transverse oscillation at Re = 850, S/L = 0.25 and H-p/L = 0.62, the Nu/Nu(0) (Nu and Nu(0) separately mean the Nusselt number of the case with and without the piezoelectric fan) of square pin-fin heat sink Model C would exceed 2. The values of Nu/Nu(0) for various heat sinks would drop and approach to unity as increasing Re. In general, under the oscillating condition, the square pin-fin heat sink gained the best heat transfer enhancement;the longitudinal plate-fin heat sink gained slightly less heat transfer enhancement than the square pin-fin heat sink did;the aluminum-foam heat sink gained poor heat transfer enhancement. In addition, the transverse oscillation promoted slightly more heat transfer enhancement than the axial oscillation did. Finally, this study proposed

关键词： Piezoelectric fan Axial mainstream Heat sink Heat transfer enhancement smoke flow visualization Experiment

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MIXING CHARACTERISTICS OF TWIN IMPINGING CIRCULAR JETS

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JOURNAL OF PROPULSION AND POWER 1995年第6期11卷 1118-1124页

作者： DISIMILE, PJ SAVORY, E TOY, N UNIV SURREY DEPT CIVIL ENGNGUILDFORD GU2 5XHSURREYENGLAND

The mixing region of two identical incompressible air jets was studied at included angles of 30 and 45 deg using total pressure surveys and quantitative flow visualization, This work has confirmed that, while the rates of decay of centerline total pressure are similar for both configurations, the growth of the 45-deg jets after impingement in the plane normal to the nozzle plane is over 52% greater than in the 30-deg case. However, in the nozzle plane the growth rates for both cases are almost identical to that of a single jet, This growth pattern produced an elliptical mixing cross section with the major axis over 2.5 times larger than the minor axis for the 45-deg case and approximately 1.6 times larger for the 30-deg jet configuration, Image analysis of the visualization studies has also shown that the half-widths of the jets grow at the same rate as the overall width of the interface region between the jet and the external fluid.

关键词： smoke flow visualization Image Analysis Propellant Nozzle Geometry Laser Induced Fluorescence Kinematic Viscosity Charge Coupled Device Combustion Stability Image Processing Plenum Chamber

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FREQUENCY MEASUREMENTS IN A FINITE CYLINDER WAKE AT A SUBCRITICAL REYNOLDS-NUMBER

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AIAA JOURNAL 1991年第12期29卷 2163-2168页

作者： BUDAIR, M AYOUB, A KARAMCHETI, K FLORIDA STATE UNIV DEPT MECH ENGNTALLAHASSEEFL 32306 KING FAHD UNIV PETR & MINERALS DHAHRAN 31261SAUDI ARABIA

A spectral study of a hot-wire investigation in the near wake of a finite circular cylinder of high-aspect ratio is reported. The measurements included frequency spectra and cross correlations in spanwise and streamwise directions. The study identifies four spanwise regions, in terms of frequency, in the immediate wake of the finite cylinder.

关键词： Vortex Shedding Phenomena High Aspect Ratio Band Pass Filter smoke flow visualization Structural Vibration Astronautics Wind Tunnels Aeronautics Anemometer

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A comparative study on the evolution of compressible vortex ring generated from a short driver section shock tube

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FLUID DYNAMICS RESEARCH 2020年第5期52卷 055504-055504页

作者： Dey, Santanu Murugan, T. Chatterjee, Dipankar Cent Mech Engn Res Inst CSIR Durgapur 713209 India Acad Sci & Innovat Res Ghaziabad 201002 India

The compressible vortex ring emanating from an ultra-short driver section shock tube is simulated using Euler and Navier-Stokes solvers for a diaphragm pressure ratio of 8.4. The numerical results are compared with smoke flow visualization experiments performed in a shock tube. Here the main focus is to compare the vortex ring evolution during its self-sustained motion as many researchers studied the vortex ring dynamics during its formation and growth stage. It is observed that the formation and interaction of Kelvin-Helmholtz (K-H) vortices generated at the trailing jet make the flow distinct in the solvers and experiments though the shock cell structures, embedded shock, and counter-rotating vortices are similar. Surprisingly in simulations, the vortex ring has regained its compact structure after its strong interactions with K-H and counter-rotating vortices. Whereas, it becomes a turbulent structure during its self-sustained motion in experiments. Further, the vortex ring simulated through a viscous solver moves downstream with a higher translational velocity compared to the inviscid solver at the later stage. The translation velocity of the vortex ring is the least in experiments and it may be attributed to the strong turbulent viscosity compared to the physical viscosity.

关键词： compressible vortex ring CFD AUSM shock tube smoke flow visualization

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Rotor free-wake modeling using a pseudoimplicit relaxation algorithm

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JOURNAL OF AIRCRAFT 1995年第6期32卷 1276-1285页

作者： Bagai, A Leishman, JG University of Maryland College Park Maryland 20742

A pseudoimplicit predictor-corrector relaxation algorithm with five-point central differencing in space has been developed for the solution of the governing differential equations of the helicopter rotor free-wake problem. This new approach is compared and contrasted with more conventional explicit-type free-wake algorithms. A convergence analysis shows that the new algorithm provides for much more rapid convergence characteristics compared to explicit methods, with improvements in numerical efficiency and predictive accuracy.

关键词： Predictor Corrector Method Fully Articulated Rotor Convergence Analysis Lamb Oseen Vortex Multirotor Freestream Velocity Rotor Blades smoke flow visualization Velocity Profiles Angle of Attack

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Experimental measurements of dynamic control surface effectiveness

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JOURNAL OF AIRCRAFT 1996年第5期33卷 880-887页

作者： Rennie, RM Jumper, EJ UNIV NOTRE DAME HESSERT CTR AEROSP RESDEPT AEROSP & MECH ENGNNOTRE DAMEIN 46556

This article reports on a low Reynolds number experimental study of the unsteady lift characteristics of an NACA 0009 airfoil pitched about its midchord, equipped with a 27% trailing-edge flap that could be independently deflected. The airfoil normal force, obtained from integrated surface pressure measurements, was captured during rapid, trailing-edge flap-only deflections;rapid, arbitrary, pitch-only excursions;and combined rapid pitch and flap-deflection motions, The measured aerodynamic response of the flapped airfoil to the various flap, airfoil, and airfoil-flap combination motions was compared to theoretical and panel-code-computed aerodynamic-response predictions. These comparisons, and the results of now visualization experiments, led to the observation that both the flap's effectiveness and the airfoil's lift-curve slope were higher during their motion than their steady-state values, and essentially matched their inviscid theoretical values.

关键词： Lift Coefficient Flap Deflection Trailing Edge Flap Pitching Airfoil smoke flow visualization Pressure Transducers Compressible flow Control Algorithm Aerodynamic Coefficients Data Acquisition System

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VORTEX DYNAMICS ANALYSIS OF UNSTEADY VORTEX WAKES

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AIAA JOURNAL 1991年第3期29卷 321-326页

作者： SUNDARAM, P KUROSAKA, M WU, JM UNIV TENNESSEE INST SPACETULLAHOMATN 37388

An incompressible inviscid unsteady vortex dynamics analysis is presented to investigate the flow details for a class of free and bounded shear flows. Using the unsteady vortex models developed for the starting vortex behind sharp edges and the vortex street wakes, particle dynamics computations have been carried out to determine the pathline and streakline patterns in each of these model flows. Based on these results, the energy equation has been integrated along particle paths. The computations reconfirm that an instantaneous separation of energy occurs in the wake. Another interesting phenomenon, termed the Eckert-Weise effect, where the near-wake region contains essentially a cold flow, has also been computationally reobtained using the present vortex model. Using a similar model, the wall-bounded vortex street wake problem has also been studied. The computed results highlight the important dynamical effects of convecting unsteady vortex motion close to a wall, which indicates that the inviscid entrainment effects play a vital role on the wall layer fluid eruption.

关键词： Karman Vortex Street Streakline Patterns Incompressible flow Freestream Velocity Energy Distribution smoke flow visualization Shear Layers Navier Stokes Equations Kinematic Viscosity Wind Tunnel Interference

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