RU2015942C1 - Apparatus to control boundary layer on aerodynamic surface of aircraft - Google Patents

Abstract

FIELD: aviation. SUBSTANCE: apparatus has swirl chamber 1, made in the form of a cavity, located in rear part of the aerodynamic surface and connected with a low pressure source 4. A streamlined body 2 is placed in swirl chamber 1. Space between bode 2 and walls of the chamber forms ring-shaped canal 3. Several swirl chambers may be positioned on surface of the rear part. In the case chambers are provided with spillways 6 with exits into common for all chambers gas dynamic canal 7, connected with source of low pressure 4. Spillway 6 with walls of the gas dynamic canal are functioning a ejectors. The gas dynamic canal may be made in the form of a canal with receiver 8. In the case, entering the receiver part of the canal from ejectors side is made in the form of diffuser 9. The receiver may be communicated with area of low pressure in flowing around stream by canals 10 with control shutters 11. Turning shutters 12 and 13 may be mounted in canals 7 and ejectors. Source of low pressure may be made as ejector 16, formed at the entrance in the diffuser of turbine-jet engine 15. EFFECT: apparatus ensures aircraft aerodynamic surface continuous air streamlining with low energy consumption. 6 cl, 4 dwg

Description

 The invention relates to aviation, and in particular to boundary layer control devices for changing the aerodynamic characteristics of an aircraft.

 When air flows around thick aerodynamic profiles in the stern, a flow with a positive pressure gradient is realized, which prevents the gas from moving in the region of the boundary layer, where the velocities are relatively small. The result of such an impact can be the separation of the boundary layer from the surface in the stern and, as a result, a significant increase in the aerodynamic drag of the profile with a decrease in lift, which together leads to a decrease in the aerodynamic quality of the streamlined surface.

 To improve the aerodynamic characteristics of the profiles, during the flow of which a positive pressure gradient in the flow causes the separation of the boundary layer from the surface in the aft part of the profile, they resort to suction of the boundary layer from the surface, which leads to an increase in the velocity in the near-wall region and allows the flow to overcome the separation realized in the feed parts are positive pressure gradients. For the boundary layer to be sucked off, a rather diverse shape of the holes and slots used for perforation is perforated. The perforated surface is in communication with the rarefaction chamber located in the inner surface of the streamlined profile. Such a constructive solution allows the necessary selection of mass from the near-wall region of the boundary layer (suction) to improve the flow around the profile.

 It is known that the boundary layer control device operating according to the principle described above is made in the form of a series of vortex chambers located on the inside of the profile with openings placed across the external flow (1).

 The vortex motion inside the chambers is supported by the hydrodynamic interaction of the vortex motion in the chamber with the external flow in the zone of the hole. In this case, the external flow velocity in the wall region increases, which leads to a continuous flow around the profile.

 However, the known device has disadvantages, the main of which are: design complexity, a high level of profile resistance and high energy consumption for suction of the vortex flow.

 The complexity of the design consists in a large number of vortex chambers and mass selection chambers.

 A high level of resistance arises from a significant profile resistance due to the poorly streamlined square shape of the chamber, and due to an increase in the friction resistance on the surface of the vortex chambers.

 The high energy consumption for the flow suction is explained by the high resistance of the lines connecting the vortex chambers to a low pressure source. The throttling effect of the highways is especially great for the sound flow realized in a known device. In addition, at low external flow rates and small values of a positive pressure gradient, the device’s energy system operates in a non-economic mode, since it, tuned to the maximum values of flow velocities and pressure gradients, sucks more than necessary, which leads to excessive energy consumption.

 A boundary layer control device is known in which vortex chambers are cylindrical in shape, which makes it possible to reduce their profile resistance (2). However, due to the small size of the gap connecting the near-wall region of the flow with the vortex chamber, the region of interaction between the flow in the chamber and the external flow is not sufficiently extended so that, in the case of large positive pressure gradients, the necessary increase in the flow velocity in the near-wall region is possible to prevent separation of the boundary layer.

 A boundary layer control device is known in which a plurality of vortex chambers with openings connecting their cavity with a wall flow form an aerodynamic profile in the form of a wavy surface with a vortex generator installed in its frontal surface (3).

 This device eliminates the disadvantage associated with the small extent of the interaction region of the external and internal vortex flow, however, it cannot be used for a wide range of flow regimes, since the frequency of vortex vanishing with the vortex generator must coincide with the frequency of passage of the wave-like surface structures by the external flow, which can be implemented by design for only one flow mode.

 A boundary layer control device is known that is used in the design of aircraft, made in the form of a thick aerodynamic profile with a number of slotted grooves located in its aft part located perpendicular to the flow and connected to a low pressure source (4). The disadvantages of this device are the high energy costs due to the large pressure drop that is overcome by the near-wall flow, since air is sucked out in places of a streamlined surface, where the pressure is minimum, and blowing in places where the pressure is maximum. Large energy costs do not allow to obtain high aerodynamic quality of the aircraft.

 The objective of the invention is to create a boundary layer control device that ensures, at low energy consumption, a continuous flow around the aerodynamic surface of an aircraft. This is achieved by the fact that in the boundary layer control device containing a vortex chamber made in the form of a cavity, a streamlined body is placed in the aortic chamber cavity in communication with the low pressure source in the vortex chamber cavity with the formation of an annular vortex channel between the chamber walls and the body surface.

 The device may contain several vortex chambers placed one after another, while the vortex chambers must be equipped with ejectors in the form of channels connecting their cavities with the flow part of the common gas-dynamic path communicated to all chambers, connected to a low pressure source.

 The gas-dynamic path can be made in the form of a channel with a receiver, while the input part of the channel to the receiver from the ejectors is made in the form of a diffuser.

 It is advisable to connect the receiver cavity with the low-pressure region above the streamlined surface of the channels with the dampers controlled at the channel exit. It is advisable to place control dampers in the channels of the gas-dynamic path.

 The low pressure source can be made in the form of an ejector located in the inlet diffuser of a turbojet engine.

 The presence of a streamlined body in the cavity of the vortex chamber allows, due to the natural pressure gradient, to obtain a circulating flow regime that ensures continuous flow around the surface at low suction levels and thereby reduce energy consumption by several times compared to the prototype.

 The use of a system of several vortex chambers equipped with ejectors, united by a common gas-dynamic path, can further reduce energy costs.

 The system of ejectors with a single gas-dynamic path allows the use of high-pressure air, which is taken in large quantities from the feed cells, for ejection, which also reduces the energy consumption for suction.

 The presence of a diffuser allows you to restore the pressure in the receiver, which leads to a decrease in the required level of reduced pressure provided by the suction source, and thereby further reduces energy consumption.

 The connection of the receiver with the low-pressure region in the stream flowing around the surface allows one to discharge part of the suction air into this region, providing an even greater reduction in energy consumption for the operation of the suction source.

 The use of control flaps in the system allows optimizing suction levels at various flow modes. In addition, the presence of flaps during braking of the aircraft provides a partial or complete separation of the flow (depending on the intensity of braking) with a slight decrease in lift.

 The use of an ejector at the inlet of a turbojet engine as a source of low pressure makes it possible to obtain an effective source of suction.

 The invention is illustrated by drawings, where in FIG. 1 shows a section of an aircraft in the form of a thick aerodynamic profile with a boundary layer control device with four vortex chambers located on the aft part of the surface; in FIG. 2 - section of one of the vortex chambers with an ejection channel; in FIG. 3 is a cross section of a vortex chamber (first downstream) with a diffuser part of the gas-dynamic path, a receiver and a control flap; in FIG. 4 - pressure distribution on the surface of a thick aerodynamic profile during tear-off and tear-off flow.

 The boundary layer control device consists of several vortex chambers 1, placed one after another in the aft part of the aircraft. In the cavity of the chambers a streamlined body 2 is placed with the formation of an annular channel 3 with the chamber walls. The chambers are in communication with a low pressure source 4. The first chamber 5 may not have a suction device. Each of the chambers is equipped with an ejector in the form of a channel 6, connecting the chamber cavities with the flowing part of the gas-dynamic path common to all channels, connected to a low-pressure source 4. The last chamber does not have an ejector, and its suction channel is the beginning of the gas-dynamic path, which is made in the form of a channel 7 with the receiver 8. At the same time, the entrance of the gas-dynamic path to the receiver is made in the form of a diffuser 9. The cavity of the receiver 8 is in communication with the low-pressure region in the flowing stream by channels 10 with control dampers 11. In the channel 7 ha The control channel 12, 13 and 14 can also be installed on the architechtical path and the ejector channels. A turbojet engine 15 with an ejector 16 installed in the inlet of the diffuser can serve as a low pressure source. A possible embodiment of the device (Fig. 3), in which the first downstream swirl chamber 5 does not have an ejector.

 The principle of operation of the boundary layer control device is as follows.

 When you turn on the source of air exhaust 15, a low level of pressure propagates from the ejector 16 to the receiver 8, diffuser 9 and channel 7. In channel 7, at the outlet of the ejectors 6, by setting the ejectors and dampers 14, a pressure level is established that ensures suction from the vortex chambers necessary for continuous flow around the surface . The pressure level in the channel 7 rises in the direction of the feed swirl chambers according to approximately the same law according to which the pressure in the external flow increases towards the stern of the streamlined surface.

 The diffuser 9, connecting the channel 7 with the receiver 8, reduces the speed of the suction air, increases the pressure in the receiver 8 and thereby improves the working conditions of the ejector 16 at the inlet to the diffuser of the turbojet engine, reducing the loss of the latter by reducing its throttling level.

 At the time of starting the device, suction from the vortex chambers is carried out through two channels 17 and 18 (the direction of flow in the chamber is indicated by thick lines in Fig. 2).

 After the flow is attached in the aft part of the streamlined body, pressure with a positive gradient in the direction of the stern is realized on its surface. The nature of the pressure change is illustrated in FIG. 4 solid line. A positive pressure gradient contributes to the creation of circulating motion in the vortex chambers around the streamlined body 2. In the start-up mode, after connecting the flow, it is advisable to reduce the suction levels, which is done by blocking the ejector channel 6 by the shutter 14 or the channel 7 by the shutter 12. At the same time, the suction intensity along the channels 17 and 18 declining. Since the pressure at the inlet to the channel 17 is lower than that at the entrance to the channel 18, with a decrease in the suction intensity at a certain value, the suction of air completely stops at the channel 17 and continues along the channel 18. A further decrease in the level of suction leads to circulation around the body 2, supported by the pressure drop in the channel 3, due to the pressure difference at points "A" and "B" (Fig. 2), i.e. the pressure difference in the channels 17 and 18. In the cavity of the chamber in the annular channel 3 around the body 2 a vortex is formed (thin lines in Fig. 2). In this case, the front section of the channel 17 acts as an injection channel, and the initial section of the channel 18 acts as a suction channel.

 In FIG. Figure 4 shows how the velocity profile in the near-wall region of the flow changes in several sections of the flow (its filling) due to the occurrence of a circular vortex motion around body 2, which indicates the creation of conditions for continuous flow around the surface.

 In the first vortex chambers, the circulation mode of flow can be maintained even when the suction from the chambers is completely stopped (the ejector channel is completely blocked by the shutter 14). In this case, the pressing of the external flow to the surface is ensured by suction from the subsequent chambers located downstream. The positive pressure gradient caused by the attached flow determines the conditions necessary for maintaining the circulating flow regime in the first vortex chambers in the complete absence of suction from them. The above-described surface flow mechanism explains the feasibility of performing the first downstream vortex chamber without suction from its cavity (Fig. 3). Through the channel 19 connecting the chamber 5 with the receiver 8, the gas can be blown into the cavity of the chamber 5 in a tangential direction with respect to the external flow, which intensifies the vortex movement in the first vortex chamber. The lack of suction from the first chamber 5 leads to a decrease in pressure in the channel 7, reduces the levels of vacuum required for continuous flow and thereby leads to a more economical mode of operation of the boundary layer control device. The circulation flow in the first chamber is set automatically even in the device startup mode.

 The transfer of rotary dampers from channels 6 to channel 7 of the gas-dynamic path, common to all ejectors, simplifies the device, however, it is necessary to set the ejectors of all vortex chambers to the optimal suction mode.

 To ensure the normal operation of the turbojet engine 15 at the starting modes, the control flaps 11 in the channels 10 of the receiver 8 are used. When the shutters are opened, the vacuum at the inlet to the diffuser of the turbojet engine is reduced, which prevents possible surging of the compressor of the propulsion system. The control flaps 11 at the nominal operating modes of the suction system allow to discharge into the reduced pressure area in the external stream flowing around the surface from the receiver 8 through the channels 10 a portion of the suction air, which reduces the energy consumption for the suction. To control the boundary layer during aircraft landing, it is necessary to carry out a partial separation of the flow in the aft part of the surface. To do this, the suction level is reduced by turning the shutters 14 or shutters 12 in the channel 7. Opening the bypass valves 11 also contributes to the formation of a local separation in the aft part of the surface.

 Based on the physical nature of the mechanism that is realized during the operation of the boundary layer control device, it is possible to determine the range of variation of the parameters characterizing the geometric dimensions of the vortex chamber.

ρ_ВU $\genfrac{}{}{0ex}{}{\text{2}}{\text{В}}$

;

=

, где dp/dx - градиент давления над вихревой камерой во внешнем потока;
ρ_b, U_b - соответственно плотность и скорость потока, циркулирующего в камере;
U_w - скорость на выходе из вихревой камеры во внешний поток.The maximum size L _{1 of the} vortex chamber and the minimum size h _{5 of} the ejector channel (Fig. 2) are determined by the relations
L ₁ ≃

ρ _V U $\genfrac{}{}{0ex}{}{\text{2}}{\text{AT}}$

;

=

where dp / dx is the pressure gradient above the vortex chamber in the external flow;
ρ _b , U _b - respectively, the density and speed of the flow circulating in the chamber;
U _w is the velocity at the exit of the vortex chamber into the external flow.

≥ 0,05; U_w/U_c - определяется из решений пограничного слоя;
U_c - скорость внешнего потока над вихревой камерой.As follows from the theory of separated flows, the optimal operating conditions of the device are determined by the ratio:
0.5 ≥

≥ 0.05; U _w / U _c - is determined from the solutions of the boundary layer;
U _c is the velocity of the external flow above the vortex chamber.

≥ 0;
0,3 ≥

≥ 0,01;
h₃ ≈ h₂ + (0÷2)h₄, где h₂, h₃ - минимальные размеры каналов 17, 18.The choice of U _b / U _c is determined by the following laws: an increase in the U _b / U _c ratio leads to an increase in the vortex chamber, a decrease in U _b / U _c necessitates an increase in the number of vortex chambers. An analysis based on known patterns allows one to obtain a number of relations for the main overall dimensions of the vortex chamber
0.3 ≥

≥ 0;
0.3 ≥

≥ 0.01;
h ₃ ≈ h ₂ + (0 ÷ 2) h ₄ , where h ₂ , h ₃ are the minimum sizes of channels 17, 18.

 The high level of efficiency of the patented device is due to the low suction level that is realized during its operation, which ensures continuous flow around the surface with a positive pressure gradient.

 A significant reduction in the intensity of the suction of air from the vortex chambers compared to the prototype was achieved due to the design features of the device, allowing you to create a vortex motion on the surface, increasing speed in the wall region and thereby preventing separation of the flow.

Claims (6)

 1. DEVICE FOR MANAGEMENT OF A BOUNDARY LAYER ON THE AERODYNAMIC SURFACE OF Aircraft, containing a vortex chamber made in the form of a cavity in the aft part of the surface and in communication with a low pressure source, characterized in that it is provided with a streamlined body installed in the cavity of the vortex chamber with the formation between the walls and the surface of the body of the annular vortex channel.  2. The device according to claim 1, characterized in that it is equipped with at least two vortex chambers made with ejectors in the form of channels placed one after the other, and a gas-dynamic path connected to a low pressure source, while the vortex chambers are connected to a gas-dynamic path through the channels.  3. The device according to claim 2, characterized in that the gas-dynamic path is made in the form of a channel with a receiver, while the input part of the channel to the receiver from the ejectors is made in the form of a diffuser.  4. The device according to claim 3, characterized in that the receiver is in communication with the low-pressure region above the aerodynamic surface of the channels with control flaps located at the outputs.  5. The device according to claims 2 and 3, characterized in that the control valves are located in the channels of the gas-dynamic path.  6. The device according to claims 1 and 2, characterized in that the low-pressure source is made in the form of an ejector located in the inlet diffuser of the turbojet engine.

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