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Design Exploration of a Slotted-Wing Common Research Model

A knowledge-based aerodynamic design method, Constrained Direct Iterative Surface Cur-vature (CDISC), has been leveraged for the computational design exploration of a Common Research Model with Reduced-Sweep and Slotted Wings (CRMRS-SW). Cruise-slotted-wing airfoils include a slot near the trailing edge of a main airfoil component to introduce stream air to the low-momentum, upper-surface boundary layer on a flap airfoil component with the goal of allowing for a more aft loading, relative to supercritical airfoils, without shock-induced separation. Ultimately, the cruise slotted wing is a passive technology that allows for an in-crease in the drag divergence Mach number and/or an increase in aerodynamic efficiency at agiven cruise condition. These aerodynamic benefits may be realized at the vehicle level through a trade space that includes the following design options: increasing cruise Mach number, in-creasing wing thickness, decreasing wing sweep, increasing lift coefficient and/or decreasing drag coefficient. The present study aimed to evaluate the slotted-wing concept’s potential as adrag-saving technology in application to a single-aisle transonic transport aircraft at a given cruise condition. The CDISC design method was used to develop a better understanding of the slotted-wing design variables that have a significant impact on the variability in aircraft drag and leverage this newly-developed knowledge to quantify the aerodynamic performance benefits enabled by the cruise slotted wing.

Brett R. Hiller↗

NASA NTRS1974

Investigation of the three-dimensional turbulent flow downstream of swept slot injection in hypersonic flow

Results of an experimental and numerical investigation of tangential swept slot injection (sweep angles of 22.5 and 45 deg) into a thick turbulent boundary layer at Mach 6 are presented. Film cooling effectiveness, skin friction, and flow structure downstream of the swept slot injection are investigated. The data are compared to that for unswept slots, and it is found that cooling effectiveness and skin-friction reductions are not significantly affected by sweeping the slot. Predictions of cooling effectiveness and skin friction obtained by a numerical finite-difference technique agree reasonably well with experimental surface variables. As in previous supersonic two-dimensional slot research, reduced mixing was found downstream of the slot lip in the present three-dimensional case.

Hefner, J. N.↗

NASA NTRS1975

A Theoretical Investigation of the Input Characteristics of a Rectangular Cavity-Backed Slot Antenna

Equations which represent the magnetic and electric stored energies are derived for an infinite section of rectangular waveguide and a rectangular cavity. These representations which are referred to as being physically observable are obtained by considering the difference in the volume integrals appearing in the complex Poynting theorem. It is shown that the physically observable stored energies are determined by the field components that vanish in a reference plane outside the aperture. These physically observable representations are used to compute the input admittance of a rectangular cavity-backed slot antenna in which a single propagating wave is assumed to exist in the cavity. The slot is excited by a voltage source connected across its center; a sinusoidal distribution is assumed in the slot. Input-admittance calculations are compared with measured data. In addition, input-admittance curves as a function of electrical slot length are presented for several size cavities. For the rectangular cavity backed slot antenna, the quality factor and relative bandwidth were computed independently by using these energy relationships. It is shown that the asymptotic relationship which is usually assumed to exist between the quality bandwidth and the reciprocal of relative bandwidth is equally valid for the rectangular cavity backed slot antenna.

Cockrell, C. R.↗

NASA NTRS1975

Multiple slot skin friction reduction

The paper investigates analytically the effect of multiple slot injection on skin friction for a representative fuselage shape (ogive-cylinder body) and evaluates the potential of slot injection as a drag reduction system in subsonic flow. Typical CTOL cruise flight conditions (Mach number equals 0.82 at altitudes of 11 km) were adopted for a fuselage 67.06 m in length and with maximum diameter of 7.32 m. The numerical method of Price and Harris (1972) was used to calculate the boundary-layer characteristics up to the first slot, while the finite-difference method of Beckwith and Bushnell (1971) was used to calculate the velocity profile downstream of one, three, five, or ten slots. An integral expression is proposed for characterizing skin friction reduction effectiveness, and it is seen that large reductions in viscous drag (50%) are available through slot injection. Skin friction reduction is improved by increasing the number of injection slots but at a diminishing rate.

Howard, F. G.↗

NASA NTRS1976

Direct measurements at Mach 6 of turbulent skin-friction reduction by injection from single and multiple flush slots

The surface skin-friction reduction downstream of one to four successive flush slots injecting at an angle of 10 deg into a turbulent Mach 6 boundary layer has been determined from direct measurements of surface shear. Increasing the number of succeeding slots increases the skin-friction reduction, but this trend reverses at high injection rates. The incremental improvement in skin-friction reduction decreases with increasing number of slots. Comparison with previously reported step slot data indicates that step slots with tangential injection are more effective in reducing skin friction than the present flush slot configuration. Finite-difference predictions are in reasonable agreement with skin-friction and boundary-layer profile data.

Srokowski, A. J.↗

NASA NTRS1988

Scan-independent slot arrays with parasitic wire arrays in stratified medium

The effect of a parasitic wire array on the scan admittance of a slot array has been investigated. Structures considered can consist of an infinite slot array and an arbitrary number of parasitic infinte arrays of piecewise linear wires, all arrays being embedded in a stratified medium. These include, as particular cases, phased arrays of Clavin elements. Expressing the fields from the arrays as plane waves, a procedure similar to the periodic moment method for infinite periodic structures is set up to obtain the the scan admittance of the slot array. Scan admittances are presented for a slot array with monopole arrays in free space, and a slot array with a tilted dipole array in a stratified medium. Blind spots at which the incident energy is mainly reflected rather than transmitted were found. Results obtained indicate the possibility of using parasitic wire arrays for scan compensation of active slot arrays.

Ng, Kwong T.↗

NASA NTRS1992

CFD Mixing Analysis of Jets Injected from Straight and Slanted Slots into Confined Crossflow in Rectangular Ducts

A CFD study was performed to analyze the mixing potential of opposed rows of staggered jets injected into confined crossflow in a rectangular duct. Three jet configurations were numerically tested: (1) straight (0 deg) slots; (2) perpendicular slanted (45 deg) slots angled in opposite directions on top and bottom walls; and (3) parallel slanted (45 deg) slots angled in the same direction on top and bottom walls. All three configurations were tested at slot spacing-to-duct height ratios (S/H) of 0.5, 0.75, and 1.0; a jet-to-mainstream momentum flux ratio (J) of 100; and a jet-to-mainstream mass flow ratio of 0.383. Each configuration had its best mixing performance at S/H of 0.75. Asymmetric flow patterns were expected and predicted for all slanted slot configurations. The parallel slanted slot configuration was the best overall configuration at x/H of 1.0 for S/H of 0.75.

Bain, D. B.↗

NASA NTRS1992

CFD mixing analysis of jets injected from straight and slanted slots into confined crossflow in rectangular ducts

A CFD study was performed to analyze the mixing potential of opposed rows of staggered jets injected into confined crossflow in a rectangular duct. Three jet configurations were numerically tested: (1) straight (0 deg) slots; (2) perpendicular slanted (45 deg) slots angled in opposite directions on top and bottom walls; and (3) parallel slanted (45 deg) slots angled in the same direction on top and bottom walls. All three configurations were tested at slot spacing-to-duct height rations (S/H) of 0.5, 0.75, and 1.0; a jet-to-mainstream momentum flux ratio (J) of 100; and a jet-to-mainstream mass flow ratio of 0.383. Each configuration had its best mixing performance at S/H of 0.75. Asymmetric flow patterns were expected and predicted for all slanted slot configurations. The parallel slanted slot configuration was the best overall configuration at x/H of 1.0 for S/H of 0.75.

Bain, D. B.↗

NASA NTRS1931

The Effect of Slots and Flaps on the Lift and Drag of the Mcdonnell Airplanes Determined in Flight

This note contains the results of flight test conducted by the National Advisory Committee for Aeronautics on a low-wing monoplane equipped with leading-edge slots extending over the entire wing and flaps extending only to the ailerons, to find their effect on the lift and drag characteristics of the airplane. Curves are given showing the lift and drag characteristics of the airplane for the following conditions of the slots and flaps neutral; slots closed and flaps down; and slots open and flaps down. In addition, the high and low speed in level flight and the climbing characteristics are given. The results show that the slots used alone increase the maximum lift coefficient 54 per cent; the flaps alone increase it 38 per cent; and the slots and flaps in combination decrease the landing speed from 60 to 43 m.p.h.; increase the speed range of the airplane 40 per cent; and increase the glide angle at landing speed 4.2 degrees.

Soule, Hartley A↗

NASA NTRS1932

Effect of length of Handley Page tip slots on the lateral-stability factor, damping in roll

Tests have been made in the NACA 7 by 10 foot wind tunnel on a Clark Y wing model equipped with various lengths of Handley Page slots extending inward from the wing tips. The slot lengths tested ranged from 20 to 100 per cent of the semi span. The effect of slot lengths on damping in roll was determined by means of both free-autorotation and forced-rotation test. In addition, the maximum lift coefficient was found with each slot length. The optimum length of slot for satisfactory damping in roll over a large range of angles of attack was found to be slightly over 50 per cent of the semispan for the form of slot tested.

Weick, Fred E↗

NASA NTRS1934

The effects of equal-pressure fixed slots on the characteristics of a Clark Y Airfoil

A type of fixed open slot so arranged that no flow would pass through it at a lift coefficient corresponding to high-speed flight was investigated in the N.A.C.A. 7 by 10 foot wind tunnel to determine the possibilities of such a high-lift device for increasing the speed-range ratio of a wing. The condition of no through flow was achieved by locating the slot openings at points of equal static pressure at the design lift coefficient as determined from the pressure distribution about the plain wing. Two models of Clark Y wings with such equal-pressure slots were tested and the smoke-flow patterns about them observed. The results of this investigation show that the condition of no air flow through the slot at the desired lift coefficient is attainable. The surface discontinuities produced by the slot openings have, however, such a large effect on the drag that such slots show little promise. An appreciable increase is produced in the maximum lift and the speed-range can be as high as for the plain wing.

Harris, Thomas A↗

NASA NTRS1939

Tests of an N.A.C.A. 23012 Airfoil with a slotted deflector flap

Section aerodynamic characteristics of a large-chord N.A.C.A. 23012 airfoil with a slotted deflector flap were obtained in the N.A.C.A. 7- by 10-foot wind tunnel. The characteristics of an N.A.C.A. slotted flap and of a simple split flap are included for comparison. The slotted deflector flap was found to have a somewhat lower maximum lift coefficient and somewhat higher drag at high lift coefficients than the N.A.C.A. slotted flap. The high drag of the open slot with the deflector flap neutral indicates that the slot should be closed for this condition.

House, R O↗

NASA NTRS1996

Flowfield Measurements Inside a Boundary-Layer Bleed Slot

An experimental investigation was conducted to determine the flowfield inside a bleed slot used to control an oblique shock-wave and turbulent boundary-layer interaction. The slot was oriented normal to the primary flow direction and had a width of 1.0 cm (primary flow direction) and a length of 2.54 cm and spanned 16.5 cm. The approach boundary layer upstream of the interaction was nominally 3.0 cm thick. Two operating conditions were studied: M = 1.98 with a shock generator deflection angle of 6 deg and M = 2.46 with a shock generator deflection angle of 8 deg. Measurements include surface and flowfield static pressure, pitot pressure, and total mass flow through the slot. The results show that despite an initially two-dimensional interaction for the zero-bleed-flow case, the slot does not remove mass uniformly in the spanwise direction. Inside the slot, the flow is characterized bv two separation regions, which significantly reduce the effective flow area. The upper separation region acts as an aerodynamic throat, resulting in supersonic flow through much of the slot.

Davis, D. O.↗

NASA NTRS1998

Flowfield Measurements in a Slot-Bled Oblique Shock Wave and Turbulent Boundary-Layer Interaction

An experimental investigation was conducted to determine the flowfield inside a bleed slot used to control an oblique shock-wave and turbulent boundary-layer interaction. The slot was oriented normal to the primary flow direction and had a width of 1.0 cm (primary flow direction), a length of 2.54 cm, and spanned 16.5 cm. The approach boundary layer upstream of the interaction was nominally 3.0 cm thick. Two operating conditions were studied: M = 1.98 with a shock generator deflection angle of 6 deg and M= 2.46 with a shock generator deflection angle of 8 deg. Measurements include surface and flowfield static pressure, Pitot pressure, and total mass-flow through the slot. The results show that despite an initially two-dimensional interaction for the zero bleed-flow case, the slot does not remove mass uniformly in the spanwise direction. Inside the slot, the flow is characterized by two separation regions which significantly reduce the effective flow area. The upper separation region acts as an aerodynamic throat resulting in supersonic flow through much of the slot.

Davis, D. O.↗

NASA NTRS1994

Computational Analysis of Forebody Tangential Slot Blowing on the F/A-18

An overview of the computational effort to analyze forebody tangential slot blowing for use on the F/A-18 aircraft is presented. Tangential slot blowing generates side force and yawing moment which may be used to control the aircraft flying at high angle of attack. Computations using the isolated forebody are obtained at full-scale wind tunnel test conditions for direct comparison with available experimental data. The effects of jet exit conditions, jet length, and jet location are also studied using the isolated forebody. In addition, these computations are used to predict the effect of slot blowing at transonic maneuvering flight conditions. The effects of over- and under-blowing on force and moment production are analyzed. Non-time-accurate solutions are obtained to determine the steady-state side force and yawing moments generated by tangential slot blowing. Time-accurate solutions are obtained to study the force onset time lag of tangential slot blowing. The effect of blowing on the burst point location are then analyzed by obtaining computations using the aircraft geometry, which includes the wing, empennage, and faired-over inlets. The effect of blowing on the buffet loads on the vertical tails are analyzed using time-accurate computations. Comparison with available experimental data from full-scale wind tunnel and sub-scale wind tunnel tests are made. This computational analysis compliments the experimental results and provides a detailed understanding of the effects of tangential slot blowing on the flow field about the F/A-18.

Gee, Ken↗

NASA NTRS1961

Effects of Various Arrangements of Slotted and Round Jet Exits on the Lift and Pitching-Moment Characteristics of a Rectangular-Base Model at Zero Forward Speed

An investigation was made to determine some of the effects of various arrangements of slotted and round jet exits on the lift and pitching-moment characteristics of a rectangular-base model at zero forward speed. Jet-exit slots near the perimeter of the model usually gave larger lift-thrust ratios than slots nearer the center line when the model was near the ground, but away from the ground perimeter jets forming almost a closed jet curtain induced negative pressures on the bottom of the model and resulted in less lift than that obtained with more centrally located jets or jets with large gaps in the jet curtain. Most models with jet slots symmetrical about the pitch axis gave approximately zero pitching moments through the range of ground-board distances, but under some conditions unstable flow direction caused positive or negative pitching moments to occur. With wings attached to the models, the lift close to the ground was 10 to 20 percent less than the lift away from the ground for various configurations. The round jets gave poorer lift-thrust ratios than the slotted jets in the region of ground effect. Out of the region of ground effect the round jets gave the greatest lift-thrust ratio per unit of weight rate of flow of air, for equal jet-exit areas, and the thinnest slotted jet gave the least.

Vogler, Raymond D.↗

NASA NTRS2011

Spreadsheet Calculation of Jets in Crossflow: Opposed Rows of Slots Slanted at 45 Degrees

The purpose of this study was to extend a baseline empirical model to the case of jets entering the mainstream flow from opposed rows of 45 degrees slanted slots. The results in this report were obtained using a spreadsheet modified from the one posted with NASA/TM--2010-216100. The primary conclusion in this report is that the best mixing configuration for opposed rows of 45 degrees slanted slots at any down stream distance is a parallel staggered configuration where the slots are angled in the same direction on top and bottom walls and one side is shifted by half the orifice spacing. Although distributions from perpendicular slanted slots are similar to those from parallel staggered configurations at some downstream locations, results for perpendicular slots are highly dependent on downstream distance and are no better than parallel staggered slots at locations where they are similar and are worse than parallel ones at other distances.

Holderman, James D.↗

NASA NTRS2011

Spreadsheet Calculation of Jets in Crossflow: Opposed Rows of Slots Slanted at 45 Degrees

Holderman, James D.↗