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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Peak axial-velocity decay with single- and multi-element nozzles.

Jet peak-velocity decay data were obtained for a variety of circular and noncircular single-element and multi-element nozzles for application to externally-blown-flap STOL aircraft. These data permit a rational approach, in terms of element type and element spacing, to nozzles designed to promote mixing of the jet exhaust with the surrounding air. Rapid mixing and the resulting lower axial jet velocity decreases the noise caused by the interaction of jet impingement on the flap assembly of EBF STOL aircraft. Empirical relationships are presented that permit the prediction of peak axial-velocity decay curves for a wide spectrum of mixer-type nozzles. The data are useful also in the design of ejector-type noise suppressors and for the suppression of VTOL downwash velocities caused by vertically oriented exhaust nozzles.

Von Glahn, U. H.↗
NASA NTRS2016

Sweeping Jet Optimization Studies

Progress on experimental efforts to optimize sweeping jet actuators for active flow control (AFC) applications with large adverse pressure gradients is reported. Three sweeping jet actuator configurations, with the same orifice size but di↵erent internal geometries, were installed on the flap shoulder of an unswept, NACA 0015 semi-span wing to investigate how the output produced by a sweeping jet interacts with the separated flow and the mechanisms by which the flow separation is controlled. For this experiment, the flow separation was generated by deflecting the wing's 30% chord trailing edge flap to produce an adverse pressure gradient. Steady and unsteady pressure data, Particle Image Velocimetry data, and force and moment data were acquired to assess the performance of the three actuator configurations. The actuator with the largest jet deflection angle, at the pressure ratios investigated, was the most efficient at controlling flow separation on the flap of the model. Oil flow visualization studies revealed that the flow field controlled by the sweeping jets was more three-dimensional than expected. The results presented also show that the actuator spacing was appropriate for the pressure ratios examined.

Melton, LaTunia Pack↗
NASA NTRS1972

Peak axial-velocity decay with single- and multi-element nozzles

Jet peak-velocity decay data were obtained for a variety of circular and noncircular single-element and multi-element nozzles for application to externally-blown-flap (EBF) STOL aircraft. These data permit a rational approach, in terms of element type and element spacing, to nozzles designed to promote mixing of the jet exhaust with the surrounding air. Rapid mixing and the resulting lower axial jet velocity decreases the noise caused by the interaction of jet impingement on the flap assembly of EBF STOL aircraft. Empirical relationships are presented that permit the prediction of peak axial-velocity decay curves for a wide spectrum of mixer-type nozzles. The data are useful also in the design of ejector-type noise suppressors and for the suppression of VTOL downwash velocities caused by vertically oriented exhaust nozzles.

Vonglahn, U. H.↗
NASA NTRS2018

Computational Investigation of Nominally-Orthogonal Pneumatic Active Flow Control for High-Lift Systems

We explore the feasibility of using nominally-orthogonal jets as active aerodynamic load control for multi-element high-lift systems, and whether the nominally-orthogonal jets can offer a variety of performance improvements. These nominally-orthogonal jets inject momentum normal to the airfoil surface near the flap trailing edge, where they create a vortex that entrains flow from the opposing side and change the airfoil circulation. Lift-enhancement opportunities of trailing edge nominally-orthogonal jets have previously been studied by Malavard et al. and Blaylock et al. on single-element airfoils; however, their effect on drag was not thoroughly investigated. In this study, we investigate two- dimensional nominally-orthogonal jet effects on both lift and drag on a two-element airfoil, NLR7301. We utilize Chimera Grid Tools to generate structured curvilinear overset grids, and the Reynolds-averaged Navier-Stokes solver OVERFLOW-2 to solve for the flow field around the airfoil. We perform various computational sensitivity studies on the baseline airfoil without a jet to validate computational results against benchmark experimental data. Using a Chimera overset grid topology, we demonstrate a similar lift-enhancement effect between a nominally-orthogonal jet and a nominally-orthogonal physical tab employed at the same location on the studied airfoil. After we introduce the nominally-orthogonal jet concept, we investigate nominally-orthogonal jets with various momentum coefficient settings, C(sub µ) = 0.00 − 0.04 and present a lift-enhancement relationship ∆C(sub l) ≃ 3.59 (C(sub µ)) for this airfoil. We discuss that utilizing a nominally-orthogonal jet with C(sub µ) = 0.01 can shift the linear region of the lift curve by a ∆C(sub l) = 0.36 for the pressure side jet and by a ∆C(sub l) = −0.27 for the suction side jet. Employing a nominally-orthogonal jet is also shown effective in altering the drag. To study the impact, we carry out a drag decomposition study in the form of drag polars. We show for a given C(sub l) = 2.50, a nominally-orthogonal jet with C(sub µ) = 0.01 on the pressure and suction side of the airfoil results in 113 drag count decrements and 41 drag count increments, respectively, compared to the baseline airfoil with no jet. These results show that large and controllable changes in aerodynamic performance can be achieved by relatively small active flow control inputs using the nominally-orthogonal jets presented in this study.

Nominally-Orthogonal↗
NASA NTRS1972

Externally blown flap impingement noise.

An investigation of externally blown flap impingement noise was conducted using a full-scale turbofan engine and aircraft wing. The noise produced with a daisy nozzle installed on the engine exhaust system was greater than that produced by a conical nozzle at the same thrust. The daisy nozzle caused the jet velocity to decay about 35 percent at the flap. The presence of the wing next to the conical nozzle increased the noise, as did increasing the flap deflection. Compared with the conical nozzle, the daisy nozzle produced slightly less noise at a flap deflection of 60 deg but produced more noise at the lower flap deflections tested.

Putnam, T. W.↗
NASA NTRS1976

Measurements in the mixing region of a turbulent jet in a coflowing airstream

The mixing region of a turbulent jet is an important example of an intermittent turbulent shear flow. There are a great deal of interest in this region because of interest in jet noise and STOL aircraft which use upper surface blowing or externally blown flap configurations to increase lift. A detailed study of the one point statistical properties of a smoke laden jet was made using a combination of a laser velocimeter and a light scattering system. The jet, with a 14 to 1 contraction, was placed inside a wind tunnel where the ratio of the jet exit velocity to free stream was 5.1 to 1. All measurements are made for a jet Reynolds number of 22,600. Among the quantities measured are mean axial and radial velocities, axial and radial intensities, power spectra, mean smoke concentration, concentration intensities, concentration spectra, intermittencies and velocity-concentration correlations. The results are compared with hot-wire data where available.

Morton, J. B.↗
NASA NTRS1979

Transonic aerodynamic characteristics of a supersonic cruise aircraft research model with the engines suspended above the wing

The influence of upper-surface nacelle exhaust flow on the aerodynamic characteristics of a supersonic cruise aircraft research configuration was investigated in a 16 foot transonic tunnel over a range of Mach numbers from 0.60 to 1.20. The arrow-wing transport configuration with engines suspended over the wing was tested at angles of attack from -4 deg to 6 deg and jet total pressure ratios from 1 to approximately 13. Wing-tip leading edge flap deflections of -10 deg to 10 deg were tested with the wing-body configuration. Various nacelle locations (chordwise, spanwise, and vertical) were tested over the ranges of Mach numbers, angles of attack, and jet total-pressure ratios. The results show that reflecting the wing-tip leading edge flap from 0 deg to -10 deg increased the maximum lift-drag ratio by 1.0 at subsonic speeds. Jet exhaust interference effects were negligible.

Mercer, C. E.↗
NASA NTRS1974

Rational function representation of flap noise spectra including correction for reflection effects

A rational function is presented for the acoustic spectra generated by deflection of engine exhaust jets for under-the-wing and over-the-wing versions of externally blown flaps. The functional representation is intended to provide a means for compact storage of data and for data analysis. The expressions are based on Fourier transform functions for the Strouhal normalized pressure spectral density, and on a correction for reflection effects based on the N-independent-source model of P. Thomas extended by use of a reflected ray transfer function. Curve fit comparisons are presented for blown flap data taken from turbofan engine tests and from large scale cold-flow model tests. Application of the rational function to scrubbing noise theory is also indicated.

Miles, J. H.↗
NASA NTRS1974

Rational functional representation of flap noise spectra including correction for reflection effects

A rational function is presented for the acoustic spectra generated by deflection of engine exhaust jets for under-the-wing and over-the-wing versions of externally blown flaps. The functional representation is intended to provide a means for compact storage of data and for data analysis. The expressions are based on Fourier transform functions for the Strouhal normalized pressure spectral density, and on a correction for reflection effects based on Thomas' (1969) N-independent-source model extended by use of a reflected ray transfer function. Curve fit comparisons are presented for blown-flap data taken from turbofan engine tests and from large-scale cold-flow model tests. Application of the rational function to scrubbing noise theory is also indicated.

Miles, J. H.↗
NASA NTRS1972

EBF noise tests with engine under-the-wing and over-the-wing configurations

Noise tests of externally blown flaps with the engine under the wing and engine over the wing configurations were conducted. Flap noise data obtained on a TF-34 aircraft are discussed. Noise data obtained during a free-jet forward-speed-effect analysis are presented. Noise sources associated with upper surface flap blowing are described. Results of a small scale configuration screening study and some large scale model test data are analyzed. The noise data for the engine over wing configurations are compared with the engine under the wing configurations.

Dorsch, R. G.↗
NASA NTRS1975

Motion-base simulator study of control of an externally blown flap STOL transport aircraft after failure of an outboard engine during landing approach

A moving-base simulator investigation of the problems of recovery and landing of a STOL aircraft after failure of an outboard engine during final approach was made. The approaches were made at 75 knots along a 6 deg glide slope. The engine was failed at low altitude and the option to go around was not allowed. The aircraft was simulated with each of three control systems, and it had four high-bypass-ratio fan-jet engines exhausting against large triple-slotted wing flaps to produce additional lift. A virtual-image out-the-window television display of a simulated STOL airport was operating during part of the investigation. Also, a simple heads-up flight director display superimposed on the airport landing scene was used by the pilots to make some of the recoveries following an engine failure. The results of the study indicated that the variation in visual cues and/or motion cues had little effect on the outcome of a recovery, but they did have some effect on the pilot's response and control patterns.

Middleton, D. B.↗
NASA NTRS1977

Improvement of maneuver aerodynamics by spanwise blowing

Spanwise blowing was used to test a generalized wind-tunnel model to investigate component concepts in order to provide improved maneuver characteristics for advanced fighter aircraft. Primary emphasis was placed on performance, stability, and control at high angles of attack and subsonic speeds. Test data were obtained in the Langley high speed 7 by 10 foot tunnel at free stream Mach numbers up to 0.50 for a range of model angles of attack, jet momentum coefficients, and leading and trailing edge flap deflection angles. Spanwise blowing on a 44 deg swept trapezoidal wing resulted in leading edge vortex enhancement with subsequent large vortex induced lift increments and drag polar improvements at the higher angles of attack. Small deflections of a leading edge flap delayed these lift and drag benefits to higher angles of attack. In addition, blowing was more effective at higher Mach numbers. Spanwise blowing in conjunction with a deflected trailing edge flap resulted in lift and drag benefits that exceeded the summation of the effects of each high lift device acting alone. Asymmetric blowing was an effective lateral control device at the higher angles of attack.

Erickson, G. E.↗
NASA NTRS2000

Control of Shock Loading from a Jet in a Flexible Structure's Presence

The control of shock noise or screech from a jet near a flexible structure is discussed. The pressure from the supersonic jet consists of a shock with spiral and flapping nonaxisymmetric modes superimposed on broadband response. This shock induces a nonlinear-nonstationary loading problem associated with acoustic wave generation and propagation coupled with structural vibration. Control of the shock is achieved by placing a ring at the nozzle lip oscillating at the shock fundamental frequency. The ring prevents the shock characteristics originating in the column of the shear layer from sustaining connection with the out-of-phase surface vibration. Shock-free flow is maintained over a large pressure ratio. The peak power spectral density of the pressure due to shock fundamental and harmonics is converted to broadband level. The experiment is motivated by consideration of aircraft structural fatigue and interior noise.

Maestrello, Lucio↗
NASA NTRS1999

Control of Shock Loading from a Jet in the Presence of a Flexible Structure

The control of shock noise or screech from a jet near a flexible structure is discussed. The pressure from the supersonic jet consists of a shock with spiral and flapping nonaxisymmetric modes superimposed on broadband response. This shock induces a nonlinear-nonstationary loading problem associated with acoustic wave generation and propagation coupled with structural vibration. Control of the shock is achieved by placing a ring at the nozzle lip oscillating at the shock fundamental frequency. The ring prevents the shock characteristics originating in the column of the shear layer from sustaining connection with the out-of-phase surface vibration. Shock-free flow is maintained over a large pressure ratio. The peak power pressure level is reduced by 40 dB.

Maestrello, Lucio↗
NASA NTRSDate not supplied

Wind Tunnel Experiment of Microjet-based Flow Control on a Multi-Element High-Lift Airfoil

A wind tunnel model was designed, manufactured, and tested to evaluate the potential of active aerodynamic flow control for multi-element airfoils. The active flow control system involves so-called microjets –small, low momentum, normal to the surface jets located near the trailing edge of the flap –for controlling the lift and improving the aerodynamic performance characteristics of airplane high-lift systems. The configuration selected for this test is the NLR7301 two-element airfoil and it was tested in the Oran W. Nicks Low-Speed Wind Tunnel at Texas A&M University at a chord Reynolds number of 2.0 million and Machnumber of 0.10. This paper presents wind tunnel results for the NLR7301 in the Flap 20 and Flap 30 configurations. The wind tunnel results include surface pressure distributions, lift and pitching moment, and flow visualizations.The results of this experiment validate the effectiveness of the microjet with regards to control of lift in the linear regime for multi-element airfoils.

ARMD↗
NASA NTRS2010

Active Flow Control of Lifting Surface With Flap-Current Activities and Future Directions

The main objective is to develop effective control strategies for separation control of an airfoil with a single hinge flap. The specific objectives are: Develop an active control architecture for flow control around an airfoil with flap. Design, fabricate, a wind tunnel test of a high lift wing (with flap) with integrated actuators and sensors. Design, development and fabrication of synthetic jet actuators. Develop appropriate control strategy for application to the airfoil. Wind tunnel testing of the high lift wing at various angles of attack and flap positions with closed loop control.

Ahmadi, G.↗
NASA NTRS1976

Upper-surface-blowing flow-turning performance

Jet exhaust flow-turning characteristics were determined for systematic variations in upper-surface blowing exhaust nozzles and trailing-edge flap configuration variables from experimental wind-off (static) flow studies. For conditions with parallel flow exhausting from the nozzle, jet height (as indicated by nozzle exit height) and flap radius were found to be the most important parameters relating to flow turning. Nonparallel flow from the nozzle, as obtained from an internal roof angle and/or side spread angle, had a large favorable effect on flow turning. Comparisons made between static turning results and wind tunnel aerodynamic studies of identical configurations indicated that static flow-turning results can be indicative of wind-on powered lift performance for both good and poor nozzle-flap combinations but, for marginal designs, can lead to overly optimistic assessment of powered lift potential.

Sleeman, W. C., Jr.↗