Jet Flaps Research Articles

The use of jet flap in WIG

In the article the problem on the use of jet flap on WIG with the aim of improving its weight, maneuverability characteristics and parameters of sustainability as a factor WIG used micro flight altitudes. To determine the effectiveness of the proposed project design use of jet flaps as well as to optimize its geometric and operational parameters, calculation was performed WIG configuration equipped with wing flaps jet. Dunn modification takes into account two main, and most essential parameters for the jet flap, such as blowing angle and speed. As the authors calculate the estimated excess cases exclude method of analysis in order to further a calculation was correct and clear. From these results show that the presence of the screen allows increasing lift and jet flaps improves stability and handling of this type of aircraft.

Experimental and Numerical Investigation of Jet Flap Interaction Effects

The influence of the wing and flaps geometry on the flow field and acoustic radiation of the jet are experimentally and numerically investigated. The azimuth non-uniformity of jet acoustic field was experimentally defined with a help of far-field microphones, flow field within the jet was measured using PIV technique and numerically calculated with a help high resolution combined RANS/ILES method. The jet flaps interaction (JFI) effects was experimentally and numerically investigated at facility under modeling of real by-pass nozzle configuration and outflow parameters. The comparison between measured flow-field and noise of a jet shows that JFI excess noise is mainly related to jet deformation and increasing of velocity gradients and turbulence within jet which are induced by tip flap vortexes.

Unsteady flame-wall interactions in a reacting jet injected into a vitiated cross-flow

This paper describes measurements and analysis of the unsteady characteristics of a turbulent reacting fuel jet in a vitiated cross-flow. This problem involves coupling between the hydrodynamic stability of the jet–wall system, combustion induced gas expansion and interactions of the autoigniting jet with the wake flow. Analysis of the unsteady jet motions shows that the reacting jet flaps in a sinuous manner with an amplitude that increases with downstream distance but is relatively independent of jet-to-cross-flow momentum flux ratio, J. This study particularly focuses on unsteady flame–wall interactions in these systems, showing that even though the time averaged flame trajectory may be well removed from wall regions, its instantaneous trajectory may be very near or even attached to the wall. Specifically, for lower J jets (J<∼20), the flame intermittently attaches to the wall for some fraction of time that decreases with downstream distance and increasing J. From a practical point of view, intermittent flame–wall interactions cause an increase in the time averaged wall temperature, raising durability concerns. We suggest that this unsteady jet–wall attraction can be understood from analogies to the dynamics of co-flowing jet or wake pairs, as low J jets deflect into the cross-flow direction quickly. Side-by-side jets or wakes are “attracted” toward each other and exhibit global instabilities that are not present when they are isolated. In support of this argument, we show that data taken over the 1.7<J<7.2 range and a range of axial locations can be collapsed using the time averaged distance of the reacting jet from the wall.

Two-dimensional RANS simulations of the flow through a compressor cascade with jet flaps

With the aim to reduce the blade count in a stator row, in this paper the application of active blowing is discussed. Based on a high-speed compressor stage blade geometries for a stator cascade with jet flap implementation are developed. Two-dimensional numerical simulations of the cascade flow clarify that a reasonable appliance of the jet is particularly possible at high inlet flow angles, where the invested momentum can delay separation effects. At the compressor reference pitch the entrainment effect due to the jet energy broadens the operation range. The blowing leads to a pronounced increase of the static pressure rise of about 9% in the design point. A stepwise increase of the pitch up to 20%, which is equivalent to a blade count reduction of about 16% in the present case, is considered. The worsen flow guidance through the cascade causes a reduction of the operation range, which is regained by the jet flap. The required mass flow of the jet, chosen in pre-studies, is about 1% which is an adequate amount for practical use in an engine.

Analysis of flexible-membrane and jet-flapped airfoils using velocity singularities

A method for predicting the flow past thin airfoils in incompressible potential flow is presented. This method makes use of special singularities that directly represent the complex conjugate perturbation velocity in the plane of the airfoil. The method is developed first for rigid cambered airfoils and is then extended to problems for which it is particularly suitable, namely, the flow past flexible impervious membranes and past airfoils with jet flaps.

Asymmetric morphology of the propagating jet

Simulations of slab jets propagating in constant atmospheres are reported for a range of jet velocities and Mach numbers. At early times, the jet maintains approximate axisymmetry within a backflowing cocoon. When the jet has penetrated farther into the external medium, the symmetry is broken by sideways oscillation and the leading edge of the jet moves about within a growing lobe. The oscillation results from nonlinear resonant amplification of the initial perturbation by the Kelvin-Helmholtz instability. Finally, the jet flaps chaotically within the growing lobe. The flapping is driven by turbulent vortices in the lobe. The basic picture of Scheuer's (1982) dentist's drill model of the physical processes underlying asymmetric morphologies in radio galaxies is confirmed. The fluid motions in the lobe are found to govern the location of the drill bit. The morphology is time-dependent on relatively short time scales. 32 refs.

Spatial Stability of the Slab Jet. II. Numerical Simulations

view Abstract Citations (72) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spatial Stability of the Slab Jet. II. Numerical Simulations Norman, Michael L. ; Hardee, Philip E. Abstract Results of numerical simulations of a supersonic slab jet wiggled at different frequencies are presented and compared with the linearized spatial stability analysis performed in Paper I. Slabs with different densities and Mach numbers have been simulated. In general, results from the numerical simulations compare favorably with predictions of the linearized analysis. In all simulations the slab jet is disrupted by sinusoidal oscillation at or near the resonant wavelength of the fundamental sinusoidal mode, independent of the driving frequency. The jet then propagates behind a jet front and forms a lobe, and the jet flaps within the growing lobe. The sinusoidal oscillation approaches a wavelength corresponding to the driving frequency except when the driving frequency is much less than or significantly exceeds the resonant frequency. In addition to sinusoidal oscillation, the simulations also show weak oblique shock waves which cross the jet channel at about the Mach angle. These oblique shock waves can be identified with the first and second sinusoidal reflection modes predicted by the linearized analysis. Publication: The Astrophysical Journal Pub Date: November 1988 DOI: 10.1086/166819 Bibcode: 1988ApJ...334...80N Keywords: GALAXIES: JETS; HYDROMAGNETICS full text sources ADS | data products SIMBAD (6) NED (6) Related Materials (1) Part 1: 1988ApJ...334...70H

The compressible Coanda wall jet—an experimental study of jet structure and breakaway

An underexpanded jet issuing from a convergent slot and blowing over a surface of convex streamwise curvature was studied experimentally. The jet was confined between side walls, with the slot aspect ratio varying between 40 and 6, but tests showed that in the area of interest close to the slot the flow was effectively two-dimensional. The ratio of slot width to the radius of curvature of the downstream surface varied between 0.05 and 0.33. The main techniques used were Schlieren and shadowgraph to show the jet structure, and surface flow visualization which revealed areas of separation and reattachment. Surface static pressures were also measured on the curved surface. The curved jet proved to have a shock cell structure similar to that of a plane jet. However, the cell structure disappeared more rapidly as the outer shear layer grew more quickly due to the destabilizing effect of the curvature on the turbulence in the shear layer. Even at modest upstream jet pressures, a separated region on the Coanda surface became evident. This region was characterized by a stagnant constant pressure part followed by a region of strongly reversed flow before reattachment took place. The separation was caused by the compression at the end of the first shock cell, with reattachment taking place where expansion in the second cell started. The separated region grew rapidly as the upstream pressure was increased, until, finally, reattachment failed to occur and the jet suddenly broke away from the surface. This work is related to studies of the Coanda flare, where the jet is axisymmetric. The high level of turbulence causes rapid entrainment of air and so gives us clean combustion. However there should be more general application to devices that use the Coanda effect, varying from fluidic devices to blown jet flaps on wings.

Experiments in a Subscale Pilot Gust Tunnel

Introduction T development of a time dependent flow test facility has been attempted by a variety of methods. Mitchell employed a technique in which the model was moved in relation to the flow, passing orthogonally through an open jet wind tunnel. Oilman and Bennett employed a tunnel in which the gusts were produced by a set of airfoils mounted in a biplane arrangement on the opposite walls of a wind tunnel. As these airfoils were oscillated in a sinusoidal fashion, they induced an oscillating flow between them. Other methods include employing moving sinusoidal waves in the test section walls, oscillating the inlet section of an open circuit tunnel, an oscillating array of airfoils, and circulation control on a set of elliptical airfoils. The method which is probably the closest to that of the present investigation is due to Simmons and Platzer, who employed a pair of jet flaps. Each of the jet flaps is a fluidically oscillating jet driven by a pair of control jets, one on either side. As a consequence of an effort to develop fluidically controlled time dependent jets for application to several diverse problems,' a new technique was proposed for the construction of a high frequency gust tunnel. The method of operation of the fluidic nozzle is as follows: the flow passes through the throat of the jet nozzle (Fig. 1) and into a rapid expansion region. Because of the relative proximity of the walls, the flow must attach to one side of the expanded region or the other. This bistable condition can be strongly influenced by a small pressure difference between the two sides of the expanded channel. In a normal fluidic oscillator or a fluidically oscillating jet,' this pressure difference is supplied by a feedback system between the two sides. In the present case, this pressure difference is created by the rotating valves shown on each side of the jet. The valves are rotated out of phase with each other, so that one is open when the other is closed. The resulting flow always attaches to the closed side and thus provides a jet which oscillates from side to side. The actual gust tunnel design involves a number of these nozzles and is shown in Fig. 1. The tunnel flow passes between the individual nozzles so that the flow actually guides the tunnel flow from side to side. Some of the potential advantages of this method of gust generation are as follows: 1) high frequency capability; 2) low torque motors required; 3) capable of producing transverse or longitudinal gusts; 4) capable of producing various wave forms; 5) capable of producing programmed transverse disturbances; 6) capable of various phase relationships between components; and 7) capable of uniform flow across tunnel.

Studies of the behaviour of the scallopChlamys opercularis(L.) and its shell in flowing sea water

The hydrodynamic properties of the shell ofChlamys opercularishave been investigated and compared with other Pectinidae. The coefficient of lift increases with increasing current speed and angle of attack. Little benefit is gained by increasing the angle of attack beyond 20 °. Allometric changes in shell shape are not sufficient to counteract the increasing weight of the animal with growth. Flow patterns over the shell indicate that a smooth and attached flow over the body of the shell becomes broken up into a turbulent, eddying wake at angles of attack beyond 20 ° and at current speeds greater than 25 cm s−1. The effect of the auricles is to enhance lift at low speeds and to help maintain stability. It is postulated that large turbulence may be further reduced if the dorsal jets act as jet flaps.

Flight and Propulsion Control Integration for Selected In-Flight Thrust Vectoring Modes

The synthesis of a flight control system for an advanced air-superiority fighter equipped with jet flaps, and its flight simulator performance, is reported in this paper. Several control modes which integrate aerodynamic surfaces and engine thrust vector control are designed to enhance performance in maneuvering flight. Sustained load factor, maximum load factor, and deceleration capability are improved with the coordinated deployment of aerodynamic and propulsive control effectors. Feasibility of the control modes was verified by a fixed-base pilot-in-the-loop simulation. Air-to-air tracking results show substantial differences in fuel consumption and engine cycle fatigue rates depending on mode selection and pilot technique. Emergency modes and handling characteristics are also discussed.

A Supercavitating Hydrofoil with Mechanical and Jet Flaps Beneath a Free Surface

The flow around a supercavifating hydrofoil equipped with both mechanical and jet flaps, moving beneath a free surface, was analyzed by second-order theory, and the method of matched asymptotic expansions was used to solve the governing integro-differential equation. Hydrodynamic forces which are valid up to the second order of small angles of foil incidence and of jet deflection are determined by asymptotic expansions in terms of the jet-momentum coefficient. Moreover, it is found that Oba's correction factors are not reasonable.

A quasisteady theory for incompressible flow past airfoils with oscillating jet flaps

Quasisteady concepts are used for an approximate analysis of incompressibl e flow past airfoils with harmonically oscillating jet flaps. The instantaneous flowfield is considered as a sequence in the streamwise direction of steady flows with a properly enforced tangency condition between the jet and the external flow. The jet kinematics are found from experimentally determined jet decay characteristics, and the time-frozen jet is modeled by using Spence's steady jet flap analysis. Computed lift response shows substantial agreement with available measurements.

Discrete vortex method of two-dimensional jet flaps.

A jet flap theory is developed with the aid of a classical cooformal mapping of airfoils onto unit circles and the method is free of any restrictions on the amount of airfoil thickness, camber or angle of attack. The jet sheet is supposed to be infinitesimally thin and is approximated by a finite number of discrete vortices placed on a stagnation streamline. The strengths of vortices are determined by an iterative procedure which is set up between the transformed and the physical plane. Any one of the classical incompressible airfoil theories, such as Theodorsen and Garrick's direct method or LighthilPs inverse one, can be applied to determine the mapping function of airfoils onto unit circles. The present approximation will converge to the exact incompressible potential flow theory of two-dimensional airfoil sections with infinitesimally thin jet flaps, if the number of vortices is increased and the distances between the adjacent vortices decreased indefinitely. Furthermore, the classical Blasius formulae are modified for jet flaps with discrete vortex approximations; and lift, drag and moment of airfoils are obtained. An example of an elliptical section of 12.5% thickness chord ratio with jet flaps shows a fair agreement with Dimmock's experimental data. With the aid of Theodorsen and Garrick's direct and author's inverse method several more examples are worked out.

A Theoretical Investigation of the Jet-Flap Compressor Cascade in Incompressible Flow

The use of jet flaps gives a new possibility of achieving high turning cascades. In this paper a new theory for unstaggered cascades with jet flaps, developed under simplifying assumptions, is described. With the help of this theory, besides turning angles and lift coefficients, for the first time pressure distributions on, and jet slope distributions behind, the blades were calculated. The effect of stagger angle on the turning angles and lift coefficients is determined with the help of the Schlichting method, using the concept of the equivalent flat plate cascade. Sample calculations illustrate the theory and, at the same time, give an insight into the behavior of cascades with jet flaps in inviscid flow. Results of previously published experiments on cascades with jet flaps, where they fulfill the conditions of the theory, are compared with the theoretical results and demonstrate satisfactory agreement.

Experimental Investigation of Incompressible Flow Past Airfoils with Oscillating Jet Flaps

Experimental Investigation of Incompressible Flow Past Airfoils with Oscillating Jet Flaps

Some British Research on the Basic Aerodynamics of Powered Lift Systems

Summary:The paper mainly discusses recent R.A.E. and N.P.L. research on the aerodynamics of Direct jet lift (turbo-jet and turbo-fan), Propeller lift (tilt-wing and deflected slipstream), Jet flaps, and Boundary layer control (blowing and suction). Some of the work at Firms and Universities is also mentioned where the information has been made available for general circulation. Attention is drawn to the present state of knowledge in relation to V.T.O.L. and S.T.O.L. aircraft applications and to some major aerodynamic problems which need further study.

Jet Drag of Wings with Jet Flaps

AN analysis of the mechanism of jet drag is given by Stratford, it being suggested that jet drag is zero if the density velocity products of the free‐stream and jet are equal, among other conditions. Under certain conditions Stratford concludes that ‘negative’ jet drag (i.e. thrust augmentation) is possible.