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Circulation-controlled wings using the Coanda effect over the high-lift device (i.e., the flap) potentially enhance the wing’s lift coefficient by delaying or avoiding separation of the strongly de...

The spectral proper orthogonal decomposition method, which extracts spatially and temporally coherent modes in stationary flowfields, is used in the current paper to analyze high-speed broadband ch...

This Paper introduces a feedback-type fluidic oscillator design with adjustable frequency at a constant flow rate. Details of the internal and external flowfields were revealed by numerical simulat...

Computational solutions of the Reynolds-averaged Navier–Stokes equations have been used to understand the performance of thrust-augmenting ejectors for vertical and short takeoff and landing aircraft. These solutions show how ejector performance depends on the principle ejector design parameters, including the ejector inlet area, the diffuser exit area, and the length of the ejector duct, as well as the type and configuration of the primary jet nozzles. It is concluded that there is a relatively sharp peak in ejector performance that occurs over a relatively narrow range of inlet area ratios where the character of the flow changes from duct flow to free jet flow. Both the peak performance and the optimum inlet area ratio are seen to increase with the length of the ejector duct. Both increasing the jet entrainment rate and the addition of wall jets are shown to enhance the performance of short aircraft ejectors.

Pb = atmospheric pressure Pt1 = primary-nozzle operating total pressure Pt2 = secondary-nozzle operating total pressure Pw = wall static pressure on the coanda flap s = height of the secondary nozzle sh = backstep height of the coanda flap T = resultant thrust, Tx Tz 1∕2 Tx = axial thrust Tz = side thrust t = lip thickness of the primary-nozzle exit δp = resultant pitch thrust-vector angle, tan −1 Tz∕Tx

The aerodynamic forces and moments on a wind tunnel model of an axisymmetric bluff body are altered by induced local attachment of the separated base flow. Control is effected by an array of four integrated aft-facing synthetic jet actuators that emanate from narrow, azimuthally-segmented slots, equally distributed around the perimeter of the circular tail end within a small backward facing step that extends into a Coanda surface. The model is suspended in the wind tunnel by eight thin wires for minimal support interference with the wake. Fluidic actuation results in a localized, segmented vectoring of the separated base flow along the rear Coanda surface and induces asymmetric aerodynamic forces and moments to effect steering during flight. The aerodynamic effects associated with quasisteady and transitory differential, asymmetric activation of the Coanda effect are characterized using direct force and PIV measurements.

A novel plasma circulation control technique is proposed to overcome the disadvantage of conventional jet circulation control about the requirement for air source. By employing the plasma actuator on the trailing edge of the airfoil, the plasma-induced wall jet is tangential to the airfoil surface and served as Coanda blowing jet, which makes the trailing-edge detachment point migrate to the lower surface of the airfoil. In this way, the circulation and the lift of airfoil are directly controlled by the plasma actuator. The effectiveness of plasma circulation control on the aerodynamic characteristics improvement of NCCR 1510-7067N airfoil is demonstrated by solving the Reynolds-averaged Navier―Stokes equations. The plasma actuator is modeled with a phenomenological model by adding the body force source terms to the governing equations. The results indicate that the efficiency of plasma circulation control for lift augmentation is superior to that of conventional jet circulation control method. The lift augmentation efficiency after the location optimization reaches ΔC L /C μ = 134.86, which is much higher than the maximum lift augmentation efficiency 80 for conventional jet circulation control. The optimal location for the plasma actuator in plasma circulation control is downstream of the boundary-layer separation point with proper distance, where the plasma actuator makes the separated shear layer reattach to the airfoil surface and delays the trailing-edge stagnation by Coanda effect.

Fluidic flow control methods, such as transverse injection or suction, have been shown to be effective for thrust vector angle control of the flow issuing from a rectangular channel. The Reynolds number based on the channel height was 39,000. The objective of the current work was to explore the operating mechanism of these independent fluidic approaches and to consider the performance when they are combined in a single configuration. Suction vectors the flow via static pressure control near the jet exit, where the pressure boundary condition extends into the channel to produce finite vectoring at the exit of the jet. Transverse injection within the channel produces a recirculation zone that contributes to the vectoring effect due to the alteration of the wall static pressure distribution. The influence of suction on the vectoring performance is dependent on the level of transverse injection, with a degraded suction effect at higher transverse injection rates. Suction is effective when it is able to disturb and enhance the mixing of the jet shear layer.

15Cole, D., Glauser, M., and Guezennec, Y., “An Application of the Stochastic Estimation to the Jet Mixing Layer,” Physics of Fluids, Vol. 4, No. 1, 1991, pp. 192–194. 16Picard, C., and Delville, J., “Pressure Velocity Coupling in a Subsonic Round Jet,” Engineering Turbulence Modeling and Experiments—4, edited by W. Rodi and D. Laurence, Elsevier, Amsterdam, 1999, pp. 443–452. 17Guezennec, Y., “Stochastic Estimation of Coherent Structures in Turbulent Boundary Layers,” Physics of Fluids A, Vol. 1, No. 6, 1989, pp. 1054–1060. 18Murray, N., and Ukeiley, L. “Estimating the Shear Layer Velocity Field Above an Open Cavity from Surface Pressure Measurements,” AIAA Paper 2002-2866, June 2002. 19Sinha,N., Hosangadi,A., and Dash, S., “TheCRAFTNS Codeand Preliminary Applications to Steady/Unsteady Reaction, Multi-Phase Jet/Plume FlowŽ eld Problems,” Chemical Propulsion Information Agency, Publ. 568, Columbia, MD, May 1991. 20Sinha, N., Arunajatesan, S., and Ukeiley, L., “High Fidelity Simulation of Weapons Bay Aeroacoustics and Active Flow Control,” AIAA Paper 2000-1968, June 2000. W. J. Devenport Associate Editor

A rectangular jet was excited by controlled unsteady uid mass addition using two miniature uidic jets placed on either side of its narrow dimension.The subharmonicof the primary’s preferred jet column frequency [St(De) = fDe / Uj = 0.15]wasforced in the antisymmetricmodebecausesuch forcing persists for longerdownstreamdistances than the fundamental. Details of the phase-averaged ow® eld, velocity gradient terms, velocity spectra, and the mean and uctuating ow® elds were documented. The uidically excited mode grew and persisted in the ow beyond the potential core region. Unsteady uid mass addition of 12% (4% momentum addition) per uidic jet resulted in a 35% reduction of the potential core length and about a 60% increase in the normalized mass ux (percentages are with reference to the primary unforced jet). On the basis of the results, it appears that uidic devices have the potential for use in shear ow control applications.

The forcing technique presented here is successful in producing very large velocity perturbation levels in the main jet. Shear flow excitation using flip-flop exciters appears to be promising for use in practical applications.

Unsteady boundary-layer and surface pressure measurements were made on a circular cylinder with timevarying blowing applied from a narrow spanwise slot. The effects of mean blowing level, blowing frequency, and boundary-layer trip location were examined at a Reynolds number of 2.2 X 105 based on cylinder diameter. Timeresolved pressures were recorded using pressure sensors located on the Coanda surface and around the circumference of the cylinder. Flush-mounted hot film probes were positioned both upstream and downstream of the slot to provide a qualitative measurement of the boundary-layer characteristics. The results have shown that the shear stress just downstream of the slot was always in-phase with the plenum pressure. However, increasing reduced frequency generally resulted in increasingly larger phase lags between the application of blowing and the development of the flow over the remainder of the Coanda surface. For both steady and unsteady blowing, the jet entrained the outer flow at the slot and remained attached to the Coanda surface, provided a fully attached laminar or turbulent boundary layer was obtained just prior to reaching the slot.

An experiment studying a fluidically oscillated rectangular jet flow was conducted. The Mach number was varied over a range from low subsonic to supersonic. Unsteady velocity and pressure measurements were made using hot wires, piezoresistive pressure transducers, and pitot probes. In addition, smoke flow visualization using high-speed photography was used to document the oscillation of the jet. For the subsonic flip-flop jet, it was found that the apparent time-mean widening of the jet was not accompanied by an increase in the mass flux. Fluidically oscillated jets up to a Mach number of about 0.5 have been reported before, but to our knowledge there is no information on fluidically oscillated supersonic jets. It was found that it is possible to extend the operation of these devices to supersonic flows. The streamwise velocity perturbation levels produced by this device were much higher than the perturbation levels that could be produced using conventional excitation sources such as acoustic drivers. In view of this ability to produce high amplitudes, the potential for using a small-scale fluidically oscillated jet as an unsteady excitation source for the control of shear flows in full-scale practical applications seems promising.

An experimental investigation was conducted into the unsteady circulation control aerodynamics of a circular cylinder with periodic tangential blowing from a narrow spanwise slot. Both steady and unsteady surface pressure data were obtained for a variety of slot angles, blowing frequencies, and mean blowing coefficients. The experiments were run both transition free and transition fixed. Measurements were made of the time-dependent pressures at discrete points around the cylinder and were numerically integrated to estimate the unsteady lift and pressure drag at a section at midspan

The reverse-thrust performance of two-dimensional and axisymmetric curved deflectors, symmetrically situated with respect to the impinging jet, is analyzed through the use of Levi-Civita's method, Belotserkovsky's integral method, and the finite element method. The predicted results are shown to be in reasonable agreement with the available experimental data. The real-fluid effects such as Coanda effect, entrainment, and the pressure ratio are discussed in the light of the present inviscid flow analyses.

Accurate turbulence measurements taken in wall jet flows are difficult to obtain, due to high intensity turbulence and problems in achieving two-dimensionality. The problem is compounded when streamwise curvature of the flow is introduced, since the jet entrainment and turbulence levels are greatly increased over the equivalent planar values. In this experiment, two-dimensional straight and curved incompressible wall jet flows are simulated by having a jet blow axially over a cylinder. Hot wire measurements and some Laser Doppler Velocimetry measurements are presented for straight and curved wall jet flows. The results for the straight wall showed good agreement between the annular flow data and the rectangular data taken by previous researchers. For the jets with streamwise curvature, there was agreement between the annular and corresponding rectangular jets for the flow region closest to the slot exit. An integral analysis was used as a simple technique to interpret the experimental results. Integral momentum calculations were performed for both straight and curved annular and two dimensional wall jets. The results of the calculation were used to identify transverse curvature parameters and to predict the values of those parameters which would delineate the region where the annular flow can satisfactorily simulate two dimensional flow.

This paper describes an experimental investigation of a wall jet attached to a circular cylinder with radial injection. The injection, in amounts sufficient to produce separation and redirection of the wall jet, was made through one of several 0.014-in.-wide slits located every 30° on the cylinder surface. Both the attached wall jet and the injection jet were twodimensional incompressible. The working fluid used was air. The ratio of injection momentum at separation to the wall-jet momentum is found to be constant for a given initial wall-jet thickness b. The experiments show that this critical momentum ratio ranges from 0.27 for a small ratio of main slit width to cylinder radius b/a = 0.12, to zero for b/a = 0.518. Such momentum ratios appear to be on the opposite ends of two flow regions which meet when b/a = 0.344 for 30° injection. Here an unstable, switchlike area exists. The low injection requirements, high momentum amplification possible at large b/a could provide very efficient flow control in fluidics and VTOL craft.

Etude de jets turbulents tridimensionnels desaxes se dechargeant de canaux rectangulaires parallelement a une surface plane