Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15D—FLUID DYNAMICS, i.e. METHODS OR MEANS FOR INFLUENCING THE FLOW OF GASES OR LIQUIDS
  • F15D1/00—Influencing flow of fluids
  • F15D1/002—Influencing flow of fluids by influencing the boundary layer
  • F15D1/0025—Influencing flow of fluids by influencing the boundary layer using passive means, i.e. without external energy supply
  • F15D1/003—Influencing flow of fluids by influencing the boundary layer using passive means, i.e. without external energy supply comprising surface features, e.g. indentations or protrusions
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15D—FLUID DYNAMICS, i.e. METHODS OR MEANS FOR INFLUENCING THE FLOW OF GASES OR LIQUIDS
  • F15D1/00—Influencing flow of fluids
  • F15D1/002—Influencing flow of fluids by influencing the boundary layer
  • F15D1/0025—Influencing flow of fluids by influencing the boundary layer using passive means, i.e. without external energy supply
  • F15D1/003—Influencing flow of fluids by influencing the boundary layer using passive means, i.e. without external energy supply comprising surface features, e.g. indentations or protrusions
  • F15D1/005—Influencing flow of fluids by influencing the boundary layer using passive means, i.e. without external energy supply comprising surface features, e.g. indentations or protrusions in the form of dimples
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64C—AEROPLANES; HELICOPTERS
  • B64C23/00—Influencing air flow over aircraft surfaces, not otherwise provided for
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
  • F15B21/00—Common features of fluid actuator systems; Fluid-pressure actuator systems or details thereof, not covered by any other group of this subclass
  • F15B21/008—Reduction of noise or vibration
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/161—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general in systems with fluid flow
• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/172—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using resonance effects
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64C—AEROPLANES; HELICOPTERS
  • B64C25/00—Alighting gear
  • B64C25/001—Devices not provided for in the groups B64C25/02 - B64C25/68
  • B64C2025/003—Means for reducing landing gear noise, or turbulent flow around it, e.g. landing gear doors used as deflectors
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64D—EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
  • B64D1/00—Dropping, ejecting, releasing or receiving articles, liquids, or the like, in flight
  • B64D1/02—Dropping, ejecting, or releasing articles
  • B64D1/04—Dropping, ejecting, or releasing articles the articles being explosive, e.g. bombs
  • B64D1/06—Bomb releasing; Bomb doors
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T137/00—Fluid handling
  • Y10T137/206—Flow affected by fluid contact, energy field or coanda effect [e.g., pure fluid device or system]
  • Y10T137/2087—Means to cause rotational flow of fluid [e.g., vortex generator]

Definitions

• the invention relates to fluid flow at the rear face of a cavity.
• Cavity flows find their application spanning an entire regime of flow starting from subsonic, transonic, supersonic to hypersonic flows, with corresponding possible applications, such as car windows or roof opening and airplane landing gears (subsonic), airplane weapon bay (transonic), scramjet isolator and cavity flame holder in scramjet combustor (supersonic) and more.
• Cavity flows are categorized as open or closed based on their length to depth (L/D) ratio.
• L/D ratio A problem associated with open type cavity flows with L/D ratio less than 10, is critically the strong pressure oscillation created by the geometry. These pressure oscillations produce severe fluctuating pressure loads as well as noise levels in the vicinity of the cavity geometry which could be detrimental to the structure housing the cavity and its integrity.
• Fig. la is a schematic representation of an open cavity showing geometric configuration and nomenclature.
• L f represents the floor length which is equal to L for a rectangular cavity.
• Cavity geometry is a combination of a backward facing step and a forward facing step as shown in Fig. 2.
• the tip of the backward facing step is the leading edge (LE) of the cavity and the tip of the forward facing step is the trailing edge (TE) of the cavity.
• L leading edge
• TE trailing edge
• the freestream flow separates from the cavity leading edge, and a shear layer is formed, which bridges the entire cavity length and impinges on trailing edge of the cavity.
• a sound pulse is generated which propagates upstream through the cavity passage between the backward and the forward facing step. This pulse excites the shear layer formation at the leading edge and induces a Kelvin Helmholtz type instability, which grows during convection towards the trailing edge to form an array of vortices.
• acoustic waves After impact on the rear face, acoustic waves are regenerated which closes a feedback loop and provides self-sustained pressure oscillations. These oscillations and its associated resonance frequencies can be determined by phase relation across the feedback loop that provides constructive reinforcement of the waves.
• the spectrum of the pressure fluctuations inside the cavity is composed of associated narrow-band tones and broadband noise.
• the source of broadband is due to the free-stream and the shear layer.
• Fig. 3 shows schematically a self-sustained feedback loop associated with open cavity oscillations using the following nomenclature:
• V(A) Amplification of instability induces strong vortices.
• Fig. lb is taken from Zhang, X., Rona A. Edwards J. A. 1998 The effect of trailing edge geometry on cavity flow oscillation driven by a supersonic shear layer.
• a curved ramp is applied at the trailing edge of the cavity and extends from a point on the rear wall of the cavity to the upper edge.
• the downstream extent of the cavity is equal to the depth, D, of the cavity.
• US Patent No. 6,446,904 discloses an aircraft weapons bay high frequency acoustic suppression apparatus that includes an extendable spoiler retractably received within an aircraft weapons bay.
• An injector unit is received within the spoiler for injecting high frequency pulses of pressurized gas into the airstream.
• the injector unit includes a resonance tube in outlet fluid communication with a nozzle.
• the pulsating output of the resonance tube perturbs the flow of pressurized gas in the nozzle, effectively breaking it up into discrete slugs or pulses which then exit the nozzle and enter the airstream.
• the high frequency perturbation of the airflow across the weapons bay, created by the aircraft weapons bay high frequency acoustic suppression apparatus effectively suppresses undesirable acoustic resonance within the open weapons bay.
• 5,340,054 discloses perturbation elements located at the leading edge of a cavity to eliminate oscillations found to occur in the cavities of a structural frame moving through a fluid.
• the perturbation elements reflect any remaining oscillations out of the cavity at the trailing edge and may take the form of multiple pins of various shape and geometrical arrangement which prevents the generation and growth of vortices causing acoustic oscillations.
• the reflection of remaining oscillations out of the cavity may be accomplished by ramping the trailing edge of the cavity.
• US Patent No. 5,699,981 discloses an aircraft cavity acoustic resonance suppression system comprising a small diameter, cylindrically shaped member disposed parallel to and spaced up to a distance corresponding to about three airflow boundary layer thicknesses from the surface of the aircraft near the leading edge of the cavity and transverse of airflow thereacross, and an actuator operatively connected to the member providing selective adjustment of the spacing between the member and the aircraft surface.
• US Patent No. 6,050,527 discloses a flow control device and method for eliminating flow-induced cavity resonance within a closed or nearly closed end flow passage having an inlet opening defined between an upstream inlet edge and a downstream inlet edge.
• the passage accepts exterior fluid flow therein via the opening.
• the flow control device includes a stationary inlet guide vane having a leading edge, a trailing edge, and a number of support members to connect the vane to the inlet.
• EP 1 714 871 discloses an acoustic resonator for use in an engine including a cavity having a volume, an aperture, and a passage connecting the aperture and the cavity.
• the aperture has a profiled surface at a leading edge for delaying separation of fluid entering the passage and for reducing losses caused by fluid separation.
• the rear face geometry of the cavity is modified so as to lie on a curved convex surface when viewed in cross-section along a longitudinal axis of the cavity.
• an elliptic shape has been found to cause a steady shear layer reattachment and thereby restrict the mass flowing in and out of the cavity, leading to significant reduction or complete alleviation of the oscillations.
• Such an embodiment will be referred to as Elliptic Rear Face (ERF).
• the ellipse has a semi-major axis twice the cavity depth and a semi-minor axis that exactly spans the complete depth of the cavity.
• different aspect ratios have also been found to be effective including an aspect ratio of 1 : 1, which defines a circular surface.
• a cross-section through a longitudinal axis of the convex curved surface may describe part of an ellipse, hyperbola, parabola, general polynomial, general trigonometric function, general hyperbolic function or any general exponential function.
• the invention differs from the above-referenced paper by Zhang et al. discussed above and shown in Fig. lb in two respects.
• the curved surface preferably extends from or close to the floor of the cavity. More specifically, good results are expected if the curved surface intersects the rear wall of the cavity at a height no greater than 0.2D, where D is the depth of the cavity. Even more preferably it extends from the floor of the cavity as shown in Fig. 4.
• Zhang et al. the distance h shown in Fig.
• Fig. la and lb are schematic representations of prior art open cavities showing geometric configurations and nomenclature
• Fig. 2 shows further details of a prior art open cavity flow geometry
• Fig. 3 shows schematically a self-sustained feedback loop associated with the prior art open cavity oscillations
• Fig. 4 is a schematic representation of a modified open cavity according to an embodiment of the invention.
• Fig. 5a shows graphically computed pressure time histories on the rear face at different Mach numbers
• Fig. 5b shows graphically computed pressure time history demonstrating a complete alleviation of the oscillation shown in Fig. 5a by adopting ERF;
• Fig. 8 shows vorticity contours at different non-dimensional time
• Fig. 9 shows a comparison of experimental and computed results for a rectangular cavity
• Fig. 10 shows a comparison of computed instantaneous flow field
• Fig. lib shows surface flow patterns on the faces of an elliptic edged cavity at
• FIG. 12a and 12b show comparisons of computed and measured pressure distributions on the cavity floor at various Mach numbers;
• Fig. 4 is a schematic representation of an open cavity having modified geometry according to an embodiment of the invention.
• the solution according to the invention lies in the geometry itself and is achieved by altering the geometry at the flow impacting face and keeping the cavity size intact in terms of its length and depth.
• one of the proposed shapes is the elliptic shape of the forward facing step in the cavity to reduce the pressure oscillations and noise.
• two-dimensional CFD simulations were also made using commercially available software ANSYS-FLUENT.
• the results shown in Figs. 5a and 5b demonstrate a complete alleviation of the oscillation.
• the pressure fluctuations (pressure normalized by the freestream pressure) with time (normalized by freestream velocity and the cavity length) are quite evident for the VRF configuration and are shown in Fig.
• VRF open rectangular cavity
• ERP altered elliptic edged cavity
• the invention can be applied to many cavity applications, in particular car window/roof opening (subsonic), airplane landing gears (subsonic), airplane weapon bay (transonic), scramjet isolator and cavity flame holder in scramjet combustor (supersonic) and more, having open type configuration, where the problem associated with pressure fluctuations are maximum.
• the implementation of the invention leads to an almost uniform pressure distribution on the cavity floor which is helpful to the dropping of the load (e.g., weapon) in terms of safety and accuracy.
• the load e.g., weapon
• the invention can also be useful as a cavity flame holder design where flame stability and a proper mixing with recirculation zone is of prime interest in a combustion chamber.
• a combustion chamber requires a stable cavity for flame holding and a recirculation region inside the cavity with hot pool of radicals which reduce the induction time.
• the open type cavity according to the invention can meet both of these stringent requirements with a good degree of performance.
• Cavity flow application spans the entire range of Mach numbers, starting from subsonic, transonic, supersonic to hypersonic flows. Specific examples include flows in landing gears of aircrafts, store separation from internal cavity, isolator flow control in scramjet intakes, cavity flame holder in combustion chambers, etc. Cavity flows are categorized as open or closed based on their length to depth (L/D) ratio. In open cavity flows with L/D ratio less than 10, strong pressure oscillations are created. These produce severe fluctuating pressures as well as noise levels in the vicinity of the cavity which could be detrimental to the structure housing the cavity and its integrity. Research has been carried out to understand these unsteady pressure characteristics (e.g., Alvarez et al. (2004)), and towards control of such loads by implementing various passive and active controlling techniques (e.g., Rowley & Williams (2006)).
• a shear layer is formed, which bridges the entire cavity length.
• an acoustic field is formed that propagates upstream and excites the shear layer formation at the LE and induces a Kelvin-Helmholtz type of instability which grows during convection towards TE to form an array of vortices.
• acoustic waves are regenerated which closes a feedback loop and provides self-sustained pressure oscillations. These oscillations and its associated resonance frequencies can be determined by phase relation across the feedback loop that provides constructive reinforcement of the waves.
• the spectrum of the pressure fluctuations inside the cavity is composed of broadband noise and narrow-band tones.
• the source of broadband is due to the free-stream and the shear layer.
• the resonance frequencies (tones) were first provided by Rossiter (Rossiter 1964) who developed a semi-empirical formula and later modified as: where n is the non-dimensional frequency (Strouhal number), U ⁇ and M ⁇ are the freestream velocity and Mach number, respectively, m the integer mode number, a is an empirical constant associated with phase delay between vortex shedding and acoustic wave response in the cavity and Uc is the convection velocity of vortices over the cavity length.
• the cavity model used in the present study is a sting mounted type, and is designed in a modular form such as to change different parts of the cavity.
• the forebody of the cavity has 134mm length and a width of 69.4mm.
• the sidewalls of the cavity are made of fused silica windows to have an optical access inside the cavity depth for flow visualization and optical measurements.
• the regular rectangular cavity has a vertical rear face (VRF).
• VRF vertical rear face
• ERF elliptic shape
• the geometric configuration followed is shown schematically in Fig. 4.
• L the cavity length (L) is from the leading edge of cavity to the mid-plane of the elliptic wall (50% of the semi-major axis).
• Boundary layer measurements were required in order to provide accurate incoming velocity distribution to our 2D CFD simulations.
• staggered pitot boundary layer probes were used to measure the boundary layer over the model at the location of leading edge of the cavity.
• Oil flow visualization tests were carried out to obtain the surface flow field details using a proper mixture of Titanium Dioxide, Oleic acid, and lubricating oil. Mixture was sprayed evenly to all the surfaces of the cavity prior to each test run. Still images on all the surfaces were obtained after the test run and allowing the streak lines to dry. Standard Schlieren system with two 12", f/7.6 parabolic mirrors have been used to obtain shadowgraph images of the cavity overall flow field. A 50 Hz pulsed Xenon light source (3mm arc length) with energy of 1J and pulse width of 9 ⁇ 8 has been used to obtain the instantaneous flow images. The light source was synchronized with a IMP CMOS Camera (Phantom V211) with a capability of 2kHz frame rate and controlled through PCC 2.4 software supplied by Vision Research.
• IMP CMOS Camera Phantom V211
• Static and total pressures were measured using Honeywell sensors of suitable ranges. Pressure ports of 1.2mm diameter were made on the cavity floor (6 Nos.) and the cavity rear face (5 Nos.) for all the cavity configurations. The ports were connected to sensors through steel and polythene tubing in the tunnel. Sensor outputs were amplified and filtered using signal conditioner from National Instruments SCXI 1520/1125. Static pressures were sampled, averaged and recorded using a 16 bit NI PXI 6221 Data Card. Unsteady pressures were measured using Endevco 8510B-5 and 8530C-15 sensors, having natural frequency of 85kHz and 180kHz, respectively. Locations of unsteady pressure measurements on the cavity were at the mid-centerline of the front face and floor for VRF, and ERF.
• the entire computational domain was distributed with uniform quadrilateral cells having near wall cell spacing of the order of 0.09mm corresponding to y + of 13 on the cavity floor.
• a UDF Program was plugged into the inlet boundary condition to simulate turbulent boundary layer with 1/n-th power law similar to the experimental observation.
• Pressure far field boundary condition was applied to all the outer boundaries, and the no slip and no penetration wall boundary conditions were applied to cavity walls.
• the figure shows the formation of vortices at the LE of cavity and their downstream convection towards the TE of cavity.
• Fig. 8b shows a fresh evolution of vortex near the LE and through Figs. 8c to 8i, the convecting vortex can be clearly seen.
• the complete cycle of formation of a vortex till the reformation of another vortex at the same location can be observed in Figs. 8b to 8i.
• Fig. 9 shows the results obtained through experiments and as well computations. There is a very good agreement between our 2D computations and Rossiter' s empirical relation (indicated by various lines) and experiments. Our experimental results are also well predicted except for the 4th mode.
• the vorticity magnitude contour indicates an alleviation of the shedding of vortices from the cavity leading edge, leading to a smooth shear layer impact on the rear edge of the cavity.
• the streamlines (bottom row) also show a uniform circulatory flow for Elliptic Rear Face cavity (ERF) compared to a non-uniform oscillatory flow for Vertical Rear Face geometry(VRF). More importantly, the contours presented for the ERF configuration do not vary with time, indicating a 2-D steady state solution.
• the flow pattern on the front face and the cavity side face corroborate the off-centric two lobes and the flow lift-off appearing on the cavity floor, respectively.
• the oil flow pattern on the rear face of ERF indicates two directions, one along the freestream and the other towards the cavity depth.
• the cavity floor surface flow indicates a difference in flow field compared to VRF.
• the flow separation has reduced along the length of the cavity floor.
• Figs. 12a and 12b The pressure distributions along the cavity floor in 2D computation and at limited locations on cavity floor centerline in experiments for Mach numbers of 0.5, 0.7 and 0.9 with cavity having VRF and ERF are presented in Figs. 12a and 12b.
• Floor pressure for cavity with VRF near to the rear face location i.e., X/Lf 0.9-1.0, indicates a very high value due to the flow impact.
• the pressure trend is similar for all the Mach numbers; however, the values are different.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Aviation & Aerospace Engineering (AREA)
• Acoustics & Sound (AREA)
• Multimedia (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Analytical Chemistry (AREA)
• Aerodynamic Tests, Hydrodynamic Tests, Wind Tunnels, And Water Tanks (AREA)
• Soundproofing, Sound Blocking, And Sound Damping (AREA)
• Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)

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• 2017
  • 2017-02-02 US US16/074,963 patent/US10823207B2/en active Active
  • 2017-02-02 EP EP17714026.6A patent/EP3411598B1/en active Active
  • 2017-02-02 KR KR1020187025346A patent/KR20180114089A/ko not_active Withdrawn
  • 2017-02-02 JP JP2018541286A patent/JP6917030B2/ja active Active
  • 2017-02-02 WO PCT/IL2017/050127 patent/WO2017134666A1/en not_active Ceased

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