Patent Application
20090084906
The present teachings relate to adjusting an aerodynamic surface operable in a transonic and a supersonic flow, and more specifically to a recirculation region that is akin to a dynamic bump established by an oscillating jet in the aerodynamic surface that can reduce overall drag.
The demand for faster and more efficient aircraft is balanced with the cost of producing sufficient thrust to overcome the related drag at the desired speeds. When aircraft operate in a transonic or a supersonic regime, a flow 10 over a surface 12 of a wing 14 can form a strong normal shockwave 16 and a boundary layer 18, as shown in
Different active or passive techniques have been investigated for control of the interaction between the strong normal shockwave 16 and the boundary layer 18. With reference to
Other passive techniques not specifically illustrated can include sub-boundary layer vortex generators (i.e., small vertical tabs that extend into the boundary layer 18 from the surface 12 of the wing 14) and streamwise surface slits (i.e., vented wells), each of which can be positioned upstream of the strong normal shockwave 16. Each technique, at certain values of Mach number and angle of attack, can be shown to reduce the strength of the strong normal shockwave 16 and the associated wave drag. In addition, use of a porous surface (e.g., a plenum) at the foot of the strong normal shockwave 16 for certain values of Mach number and angle of attack can also be shown to reduce the strength of the strong normal shockwave and the associated wave drag by reducing a pressure jump across a foot 26 of the strong normal shockwave 16.
One active flow control technique can include a steady blowing jet located just upstream of the foot 26 of the strong normal shockwave 16 to again reduce its strength. While useful in some implementations, the steady blowing jet can be shown to reduce the lifting capability of the wing because of the relatively high jet momentum and mass flow rate required. In this instance, the Mach number of the airflow from the steady blowing jet can be comparable to the Mach number of the local airflow 10 over the wing 14. While the above examples remain useful in certain instances, there remains room in the art for improvement.
The present teachings generally include a system for reducing overall drag on an exterior surface of a mobile platform. The system includes a surface on which an airflow forms a boundary layer and a generally normal shockwave. The airflow is at a first velocity that is one of transonic and supersonic. An oscillating jet injects and extracts a jet flow through the surface. The jet flow is at a second velocity that is substantially less than the first velocity. A recirculation region is upstream of the normal shockwave and is disposed at least partially in the boundary layer. The recirculation region is established at least by the oscillating jet. A generally oblique wave is established by the recirculation region and weakens the normal shockwave.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present teachings in any way.
The following description is merely exemplary in nature and is not intended to limit the present teachings, their application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.
Various aspects of the present teachings can be applicable to any of a wide range of high speed, airborne mobile platforms, but is particularly useful with jet powered aircraft (e.g., but not limited to, fighter jets, commercial jets, private jets, supersonic dash aircraft, among others). The present teachings are also applicable to both unmanned and manned aircraft, e.g., directly, remotely, via automation, one or more combinations thereof, among others. In addition, various aspects of the present teachings can be applicable to any of a wide range of lift-producing or thrust-producing surfaces for aircraft (e.g., but not limited to, fixed wings, variable geometry wings, rotary wings, right semi-span wings, left semi-span wings, full-span wings, straight wings, swept wings, delta wings, horizontal tails, vertical tails, tapered wings, untapered wings, slanted wings, among others). Accordingly, the specific references to a wing, an airfoil and/or an aircraft herein should not be construed as limiting the scope of the present teachings to those specific implementations.
Moreover, certain terminology can be used for the purpose of reference only and do not limit the present teachings. For example, terms such as “upper,” “lower,” “above” and “below” can refer to directions in the drawings to which reference is made. Terms such as “front,” “back,” “rear” and “side” can describe the orientation of portions of the component within a consistent but arbitrary frame of reference which can be made more clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof and words of similar import. Similarly, the terms “first,” “second” and other such numerical terms referring to structures, systems and/or methods do not imply a sequence or order unless clearly indicated by the context.
With respect to
In one example, the oscillating jets 100 can be contained within a wing 112 of an aircraft 113. The oscillating jets 100 can be located to inject and extract the jet flow 102 at various positions along an upper surface 114 to establish the recirculation regions 106, i.e., the dynamic bumps 110, thereon. The wing 112 can be used in a transonic flow (i.e., a value of the Mach number is within a range between about 0.85 and about 1) and a supersonic flow (i.e., a value of the Mach number is within a range between about 1 and about 5). In these flows and with reference to
In various examples, the jet flow 102 that establishes the recirculation regions 106 can produce an oblique wave 120 that can be a weak oblique shockwave. The oblique wave 120 can interact with the normal shockwave 118 to reduce wave drag experienced by the wing 112 in the transonic and the supersonic flows. In light of this disclosure, it will be appreciated that without the jet flow 102 from the oscillating jets 100, the normal shockwave 118 can be similar to the strong normal shockwave 16 (
It will also be appreciated in light of the disclosure that the dynamic bumps 110 can reduce the overall drag of the wing 112 in a similar fashion to the fixed physical surface bumps 16, as shown in
The jet flow 102 from each of the oscillating jets 100 can be generally transverse (e.g., about 90 degrees) to the wing, as illustrated in predicted results shown in
While not specifically shown, each of the oscillating jets 100 can include, for example, an autonomous zero-net-mass flux electromagnetic (or piezoelectric) oscillatory jet actuator that can provide the oscillation between suction and blowing. In other examples, a piston and a cylinder assembly can provide the oscillation between suction and blowing. The oscillating jets 100 can further include a light weight electromagnet that can be used to actuate the piston and the cylinder assembly. Suitable electromagnets can be found, for example, in certain commercial vibration shaker applications. Other suitable oscillating jets 100 and associated systems and components are disclosed in commonly assigned U.S. Pat. Nos. 6,713,901 and 6,471,477, which are hereby incorporated by reference as if fully set forth herein.
With reference to
With reference to
For example, a recirculation region 106a (
In the various aspects of the present teachings and with reference to
The first set 100a, the second set 100b, etc. of the oscillating jets 100 can be associated with certain chord positions and/or span positions, so that activating and deactivating certain jets can correspond to certain locations on the wing 112 or other suitable aerodynamic surfaces. In addition, as flight conditions (e.g., Mach number, etc.) and wing orientation (e.g., angle of attack, etc.) change, the amount of oscillating jets 100, either active or inactive, can change. Further, the fashion in which each of the oscillating jets 100 oscillates (i.e., magnitude, frequency, etc.) can change as flight conditions and/or wing orientation change.
In one aspect of the present teachings and with reference to
The benefits of establishing the recirculation regions 106, i.e., the dynamic bumps 110, with the jet flow 102 from the oscillating jets 100 can be shown using, for example, a computational fluid dynamics tool whose accuracy can be previously established for a baseline airfoil and a control airfoil such as a NACA-64A010 airfoil through comparisons with experimental wind tunnel data. The tool can be CFL3D which is a Navier-Stokes computational fluid dynamics code developed at NASA Langley Research Center. The tool can be used to simulate the transverse oscillating jets 100 at a number of chord and/or span positions along the airfoil. The assumptions of the flow and the airfoil and the configuration of the oscillating jets 100 are provided in the following table.
Based on these results, the baseline mean overall drag coefficient (i.e., CD) can be predicted to be about 0.0329, which can be generally shown at 200, while the mean overall drag coefficient with one of the oscillating jets 100 at about 90% chord can be predicted to be about 0.0332, which can be generally shown at 202. This is about a 0.91% increase in the mean overall drag relative to the baseline, which is about a three count increase. A three count increase is equal to a 0.0003 increase in drag coefficient, such that one count is equal to 0.0001. The mean overall drag coefficient with one of the oscillating jets 100 at about 68% chord can be predicted to be about 0.0325, which can be generally shown at 204. This is about a 1.2% decrease in the mean overall drag relative to the baseline 200, which is about a three count decrease. Moreover, the mean overall drag coefficient with an active jet at about 53% chord can be predicted to be about 0.0315, which can be generally shown at 206. This is about a 4.3% decrease in the overall drag relative to the baseline 200, which is about a fourteen count decrease.
In one instance, one of the oscillating jets 100 can be positioned at about 53% chord and the slot can have a nondimensional width of about 0.0044. The predicted mean overall drag coefficient can be about 0.0315, which can be generally shown at 212 and can be about a fourteen count decrease. The fourteen count decrease can be equivalent to about a 4.3% predicted reduction in the overall drag level relative to the baseline 200. In another instance, one of the oscillating jets 100 can be positioned at about 53% chord and the slot can have a nondimensional width of about 0.0080. The predicted mean overall drag coefficient can be about 0.0305, which can be generally shown at 214 and can be about a twenty four count decrease. The twenty four count decrease can be equivalent to about a 7.3% predicted reduction in the overall mean drag level relative to the baseline 200.
It will be appreciated that in light of the disclosure, certain configurations of the slot and certain positioning of the oscillating jets 100 can maximize the percent reduction in overall drag for an aircraft traveling in the transonic and the supersonic regimes. In one example, a row of the oscillating jets 100 can be located at a certain chord position and extend generally along the span of wing 112. In other examples, the oscillating jets 100 can be positioned as to cover portions of the wing along portions of the chord and portions of the span. In this instance, certain oscillating jets 100 can be placed in the active condition and regulated accordingly.
By reducing the overall drag, the oscillating jets 100 in accordance with the present teachings can be shown to improve the lift-to-drag ratio and, therefore, improve the aerodynamic efficiency of the wing or other suitable aerodynamic surfaces that can be included with airfoils, wings, rotor blades, wind turbine blades, compressor and turbine blades, etc. Further benefits can include the reduction of fuel consumption which, in turn, can reduce fuel costs especially for commercial aircraft flying at current cruise speeds. Even more so, the range and cruise speed of a commercial aircraft can be increased, while the noise produced by the shockwave can be decreased.
In further aspects of the present teachings, the oscillating jets 100 can be used to control the aircraft attitude by modulating the aerodynamic forces (e.g., lift, drag) and moments (e.g., roll, yaw, roll) that can be acting on the aircraft at transonic and supersonic speeds.
While specific aspects have been described in this specification and illustrated in the drawings, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the present teachings, as defined in the claims. Furthermore, the mixing and matching of features, elements and/or functions between various aspects of the present teachings may be expressly contemplated herein so that one skilled in the art will appreciate from the present teachings that features, elements and/or functions of one aspect of the present teachings may be incorporated into another aspect, as appropriate, unless described otherwise above. Moreover, many modifications may be made to adapt a particular situation, configuration or material to the present teachings without departing from the essential scope thereof. Therefore, it may be intended that the present teachings not be limited to the particular aspects illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out the present teachings but that the scope of the present teachings will include many aspects and examples following within the foregoing description and the appended claims.
