WO2009116932A1

WO2009116932A1 - Improvement of the aerodynamic properties of ground vehicles

Info

Publication number: WO2009116932A1
Application number: PCT/SE2009/050267
Authority: WO
Inventors: Sam Fredriksson; Magnus Svensson
Original assignee: SEMCON CARAN AB
Current assignee: SEMCON CARAN AB
Priority date: 2008-03-17
Filing date: 2009-03-17
Publication date: 2009-09-24
Anticipated expiration: 2010-09-17
Also published as: SE532164C2; SE0800614L

Abstract

The aerodynamic properties of a ground vehicle are improved by means of an airflow control system arranged on the vehicle in such a manner that an airflow around the vehicle is influenced, so that when the vehicle travels at a particular speed the drag on the vehicle is lower than if the vehicle had traveled at this speed without the system. The system includes an air modulator (210) and at least one air intake (241', 242', 24n'). The air intake/s (241', 242', 24n') receive/s input air (A_in) via an external surface of the vehicle, and based thereon, the air modulator (210) produces a disturbance flow (F_D) influencing the airflow around the vehicle. The disturbance flow (F_D) has an intensity that varies with an oscillation frequency, which in turn, is cont-rollable by the input air (A_in) via a valve means (220). Hence, the oscillation frequency depends on a flow magnitude of the in-put air (A_in).

Description

Improvement of the Aerodynamic Properties of Grou nd Vehicles

THE BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates generally to the improvement of the aerodynamic properties of ground vehicles, such as trucks, busses, trains, trailers, passenger cars, hovercrafts and motor- cycles. More particularly the invention relates to an airflow control system according to the preamble of claim 1 and a ground vehicle according to the preamble of claim 13.

Various solutions are known for improving the aerodynamic properties of a so-called bluff body, i.e. a non-streamlined shape that produces considerable resistance when moving through the air, or a similar medium. Typically, a region of separated airflow occurs over a large portion of the surface of a bluff body. This results in a high drag force and a large wake region. The airflow often exhibits unsteadiness in the form of periodic vortex formation and shedding. Naturally, these effects are undesired. Therefore, to obtain low fuel consumption, bluff-body vehicle shapes should generally be avoided. However, for ground vehicles (trucks, busses and trailers in particular) various regulations place restrictions on the vehicles' maximum outer dimen- sions. Thus, in order to economize the available vehicle volume, heavy vehicles are normally designed with a shape which to a large extent indeed is a bluff body, i.e. where the front and back surfaces are essentially flat, vertical walls. Here, to reduce the known drawbacks of such a vehicle shape, various airflow cont- rol systems may be used to improve the aerodynamics. For example the US patents 3,910,623, 4,460,055, 5,407,245 and 5,908,217 describe different designs intended to control a vehicle's aerodynamic properties by receiving air via one or more inlets on the vehicle's body surfaces, eject this air through one or more outlets, and thus reduce the drag on the vehicle, or by other means improve the vehicle's aerodynamic properties.

The published international patent application WO 2006/080873 describes how the aerodynamic properties of bluff-body shaped ground vehicles are improved by means of air modulators, which each includes a number of openings arranged along an essentially straight line. The air modulators are controlled to produce output air in the form of vortices outside each opening. These air vortices have spin axes that in proximity to the openings are essentially perpendicular to a forward driving direction of the vehicle. Preferably, the oscillating frequency depends on the speed of the vehicle.

The US patent 6,378,932 discloses another solution for reducing a ground vehicle's air resistance. Here, an active flow-influencing structure is controlled in a periodic manner, such that time- dependant disturbances are introduced into an airflow around the vehicle. Also in this case, the frequency of the disturbances is preferably a function of the speed of the vehicle. Hence, a road-speed sensor may cause production of a control signal to the flow-influencing structure.

Although the above active-flow designs are generally more efficient than the earlier constant/non-varying flow designs, the active-flow designs may be disadvantageous because they require a more complex, unreliable and/or expensive control means.

SUMMARY OF THE INVENTION One object of the present invention is therefore to provide a solution, which alleviates the above-mentioned problems, and thus enables an uncomplicated, cost-efficient, reliable and yet flexib- Ie and adaptive aerodynamics control for ground vehicles.

According to one aspect of the invention, these objects are achieved by the initially described airflow control system, wherein the air modulator includes a valve means controllable by the input air. Specifically, the valve means is configured to control the oscillation frequency in response to a flow magnitude of the input air.

An important advantage attained by this system is that the oscillation frequency can be varied depending on the vehicle speed in a very straightforward manner.

According to one embodiment of this aspect of the invention, the airflow control system includes a pressurizing means configured to receive ambient air from outside the vehicle and supply compressed air to the air modulator. The air modulator is further configured to produce the disturbance flow based on the compressed air. Hence, an adequate amplitude of the disturbance flow can be guaranteed irrespective of the vehicle speed.

According to another embodiment of this aspect of the invention, also the pressurizing means is configured to receive input air via an external surface of the vehicle. Moreover, the air modulator is configured to produce the disturbance flow, such that a maximum magnitude thereof depends on the flow magnitude of the input air. Namely, it is normally preferable if both the frequency and the amplitude of the disturbance flow are functions of the vehicle speed, or more precisely positively correlated with the flow of input air.

According to yet another embodiment of this aspect of the invention, the pressurizing means includes a compressor configured to receive the input air, and in response thereto produce the compressed air. Thereby, the efficiency of the design can be further improved.

According to still another embodiment of this aspect of the in- vention, the air modulator includes a tube member having at least one ejector opening to an interior volume of the tube member. A rotatable member is arranged within the interior volume of the tube member, and the rotatable member is configured to allow a varying amount of the compressed air to escape through the at least one ejector opening, so as to constitute a component of the disturbance flow. This provides a highly efficient and uncomplicated control of the disturbance flow. For example, the rotatable member may include at least one bloc- king means, and this means may be configured to: cover one or more ejector openings when the rotatable member has a rotation angle within at least one first angular range; and uncover said ejector opening(s) when the rotatable member has a rotation angle within at least one second angular range.

According to a further embodiment of this aspect of the invention, the at least one blocking means has at least one internal opening configured to allow a through-passage of the compressed air within the interior volume of the tube member. Hence, the compressed air may be distributed relatively uniformly within the air modulator.

According to another embodiment of this aspect of the invention, the rotatable member has a central axle to which the at least one blocking means is attached. The central axle, in turn, has an internal void configured to transport the compressed air. Preferably, the central axle includes at least one opening connecting the internal void of the central axle with the interior volume of the tube member. Thereby, the compressed air may be conveniently forwarded to the respective ejector openings.

According to yet another embodiment of this aspect of the in- vention, the at least one blocking means is configured to allow the compressed air to flow inside the tube member in parallel with the central axle. This is beneficial, since it both facilitates forwarding compressed air to the ejector openings and enables a uniform air distribution within the air modulator. According to still another embodiment of this aspect of the invention, the airflow control system includes a fan means and at least one conduit arranged to forward the input air to the fan means. The fan means is mechanically connected with the rotat- able member, so as to cause rotation thereof in response to a rotation of the fan means, and said conduit/s, in turn, suppl/y/ies air to the fan means when the vehicle is propelled. Thus, the air modulator will produce the disturbance flow, such that the frequency thereof depends on the speed of the vehicle.

According to a further embodiment of this aspect of the invention, the airflow control system includes a gear box connecting the fan means to the rotatable member. Of course, this allows an improved flexibility in terms of the relationship between the vehicle speed and the oscillation frequency of the disturbance flow.

According to another aspect of the invention, these objects are achieved by the initially described ground vehicle, wherein the vehicle includes at least one of the above-proposed airflow control systems. The air modulator of each system is here arran- ged on the vehicle, such that when the vehicle travels at a particular speed an amount of vortex shedding behind the rear surface is lower than if the vehicle had traveled at this speed without the at least one system.

According to one embodiment of this aspect of the invention, each air modulator is arranged such that the ejector opening/s thereof is/are located downstream of a flow separation line at which flow separation had occurred during propulsion of the vehicle if no disturbance flow had been produced. Namely, at such locations the air modulators interact efficiently with the air- flow around the vehicle. The air modulators may be arranged on essentially any exterior vehicle surface, i.e. on the main upper surface, on the bottom surface, on the side surfaces and/or on the rear surface. According to another embodiment of this aspect of the invention, at least one air intake of the airflow control system is arranged on the general front surface of the vehicle. Preferably, one or more air intakes are arranged in so-called high-pressure zones on the vehicle's body. A high-pressure zone is an area in proximity to which during propulsion of the vehicle an air pressure is developed, which substantially exceeds the pressure level at the air modulator (i.e. where the disturbance flow is introduced into the airflow around the vehicle). In most cases, this means that the pressure level in the high-pressure zone exceeds the atmospheric pressure level.

In addition to the above-mentioned advantages, the invention is beneficial in that it reduces the amount of soiling of the vehicle's exterior surfaces that results from the global vortices behind the vehicle. Moreover, by applying the invention, the average wind noise level caused by a vehicle in motion can be reduced in an uncomplicated manner.

Further advantages, advantageous features and applications of the present invention will be apparent from the following desc- ription and the dependent claims.

BRIEF DESCRI PTION OF THE DRAWINGS The present invention is now to be explained more closely by means of embodiments, which are disclosed as examples, and with reference to the attached drawings. Figure 1 illustrates how vortex shedding arises behind a ground vehicle without any airflow control mechanisms,

Figure 2 shows a ground vehicle equipped with an airflow control system according to one embodiment of the invention,

Figure 3 illustrates schematically how the input air is used to control the oscillation frequency of the distur- bance flow according to one embodiment of the invention,

Figures 4a-c illustrate the operation of the proposed valve means of the air modulator according to a first embodiment of the invention, and

Figures 5a-c illustrate the operation of the proposed valve means of the air modulator according to a second embodiment of the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION We refer initially to Figure 1 , which shows a ground vehicle 10 that travels in a forward direction D_F. The vehicle 10 is not equipped with any airflow control mechanisms. Therefore, due to the vehicle's 10 pronounced bluff-body shape, a relatively large amount of vortex shedding 16 arises behind the vehicle 10.

Figure 2 shows a side view of a ground vehicle 100 equipped with an airflow control system according to one embodiment of the invention. In Figure 2, the system includes three air modulators 210a, 210b and 210c respectively. However, according to the invention, any number of air modulators is conceivable. Moreover, although the vehicle 100 in Figure 2 exemplifies a truck, the invention is equally well applicable to other types of ground vehicles, such as busses, trains, trailers, passenger cars, hovercrafts and motorcycles. In any case, it is presumed that the vehicle 100 has a body with an outer surface including a general front surface 1 10, a bottom surface 1 15, a main upper surface 120, two side surfaces, and a rear surface 140. As can be seen in Figure 2, the general front surface 1 10 extends also over an almost horizontal surface of the vehicle's cabin. Namely, in this specification, a transition from the general front surface 1 10 to the main upper surface 120 is defined to be at the front- most part of a horizontal vehicle top surface of substantial length. Thus, for trucks, the main upper surface 120 is normally delimited by the front and back edges of the vehicle's cargo space. However for other types of vehicles, other delimitations may be applicable.

The air modulators 210a, 210b and 210c are configured to influence the airflow F around the vehicle 100, such that when the vehicle 100 travels at a particular speed (and wind conditions) the drag on the vehicle 100 is lower than if the vehicle 100 had traveled at this speed (and wind conditions) without the system. For example, the proposed system may create small-scale air vortices adjacent to shear layers of the airflow F around the vehicle 100. This, in turn, perturbates the airflow F and thus weakens the strength of any of global vortex shedding behind the vehicle 100.

The airflow control system according to the invention includes at least one air intake 241 ' and 251 ' adapted to receive input air A_in via an external surface of the vehicle 100. Here, the air intakes are exemplified by a central opening 241 ' in the front surface 1 10 and a highly located opening 251 ' adjacent to the main upper surface 120. According to the invention, the air intakes may be placed at any external surface of the vehicle 100. Never- theless, according to a preferred embodiment of the invention, at least one air intake is arranged in a so-called high-pressure zone on the vehicle's 100 body. A high-pressure zone is a body area in proximity to which, during propulsion of the vehicle 100, an air pressure is developed that substantially exceeds the pressure level where the air modulator 210 is located (i.e. where the disturbance flow F_D is introduced into the airflow F around the vehicle 100). Thus, the pressure level in the high-pressure zone may be a factor 1 .1 , or more, of the ambient air pressure level outside the air modulator 210. It is advantageous to arran- ge the air intakes in high-pressure zones because thereby comparatively high flow levels of input air A_in can be accomplished by means of a relatively small opening in the vehicle's 100 exterior surface. Moreover, provided that the pressure level in the high-pressure zone exceeds the general atmospheric pressure level, taking input air A_in from a high-pressure zone may mitiga- te the air resistance effects that such a zone typically is associated with. For example the amount of undesired separation zones can be decreased.

The airflow control system also includes an air modulator 210 configured to produce a disturbance flow F_D, which influences the airflow F around the vehicle 100. The disturbance flow F_D has an intensity that varies with an oscillation frequency. To accomplish this, the air modulator 210 includes a valve means that is controllable by the input air A_in. Specifically, the propo- sed valve means is configured to control the oscillation frequency in response to a flow magnitude of the input air A_in received via the air intakes 241 ' and 251 . Since, generally, the flow magnitude of the input air A_in is positively correlated with the vehicle speed, a relatively high vehicle speed will result in a comparatively high oscillation frequency, and vice versa; a relatively low vehicle speed will result in a comparatively low oscillation frequency.

The design of the valve means will be discussed in detail below with reference to Figures 3, 4 and 5. As is apparent in these drawings, each air modulator 210a, 210b and 210c has at least one ejector opening. According to one embodiment of the invention, at least one of the air modulators 210a, 210b and 210c is arranged, such that its ejector openings are located downstream of a flow separation line FSL at which flow separation had occurred during propulsion of the vehicle 100 if no disturbance flow F_D had been produced by the air modulator in question. Naturally, irrespective of the location of any flow separation lines FSL, the proposed air modulators 210a, 210b and/or 210c may be arranged on any exterior surface of the vehicle 100, i.e. on the main upper surface 120, the bottom surface 1 15, the side surfaces and/or the rear surface 140.

On a vehicle, which in contrast to the vehicle 100 shown in Figure 2, has relatively rounded edges between the rear surface and the side surfaces, between the rear surface and the bottom surface and/or between the rear surface and the top surface, the air modulators are preferably arranged somewhat closer to the center point of the vehicle.

It should be borne in mind that the air modulator positions 210a, 210b and 210c shown in Figure 2 merely constitute illustrative examples of suitable locations. According to the invention, however, air modulators may likewise be positioned at the rear surfaces of any fender wings on the vehicle 100. Moreover, one air modulator can be arranged along each bodyline of the vehicle 100 where flow separation occurs. Hence, if the vehicle

100 has a protruding engine hood, air modulators may also be positioned proximate to any edges of this hood.

To enhance the efficiency of the air flow control system, the system may include a pressurizing means 250 configured to receive ambient air from outside the vehicle 100 and supply compressed air Fp (i.e. at an elevated pressure level) to the air modulator 210. In such a case, the air modulator 210a, 210b and/or 210c is configured to produce the disturbance flow F_D based on the compressed air F_P. Naturally, this does not preclude that one or more of the air modulators 210a, 210b and 210c also receives the input air A_in directly from at least one air intake 241 ' and/or 251 '.

According to one embodiment of the invention, the pressurizing means 250 is configured to receive input air A_in via an external surface of the vehicle 100, e.g. through one or more air intakes 241 ' and/or 251 ' as illustrated in Figure 2. The air modulator 210 is configured to produce the disturbance flow F_D, such that a maximum magnitude thereof depends on the flow magnitude of the input air A_in. Thus, at given wind conditions, the disturbance flow F_D magnitude is proportional to the vehicle speed. In other words, a peak-to-peak amplitude of an air speed exiting from each opening is comparatively high for relatively high vehicle speeds, and vice versa; comparatively low for relatively low vehicle speeds. Preferably, the peak-to-peak amplitude is equiva- lent to approximately 0,5 time to approximately 10 times the vehicle speed, and more preferably, the peak-to-peak amplitude is equivalent to approximately 1 time to approximately 3 times the vehicle speed. The vehicle speed here represents the so- called freestream velocity, i.e. the speed at which the airflow F passes the vehicle 100.

According to one embodiment of the invention, the pressurizing means 250, in turn, includes a compressor 260 and a pressure tank 270. The compressor 260 is configured to receive the input air A_in (e.g. via the air intake 251 '), and in response thereto produce compressed air F_P, which is supplied to the pressure tank 270. However, as a complement, or an alternative thereto, the pressure tank 270 may receive the input air A_in from an air intake 241 ', preferably via a valve means 280. The valve means ren- ders it possible to control the input flow into the pressure tank 270, and thus adjust the pressure level therein.

We now refer to Figure 3, which illustrates schematically how the input air A_in is used to control the oscillation frequency of the disturbance flow F_D according to one embodiment of the inven- tion. Figure 3 symbolically shows a number of air intakes 241 ', 242' up to 24n' for receiving input air A_in. For simplicity, it is further symbolically demonstrated that the conduits 241 , 242 up to 24n from all air intakes 241 ', 242', 24n' are joined into a common conduit 240 of one air modulator 210. However, according to the invention, any number of air intakes 241 ', 242', 24n' may be used to feed input air A_in to any number of air modulators 210.

Anyhow, as mentioned above, the air intakes 241 ', 242', 24n' are adapted to receive input air A_in via an external surface of the vehicle 100; and the air modulator 210 is configured to produce a disturbance flow F_D that influences the airflow F around the vehicle 100. The disturbance flow F_D has an intensity that varies with an oscillation frequency, which in turn, depends on a flow magnitude of the input air A_in. According to the invention, this relationship is accomplished by a valve means 220 in the air modulator 210. The valve means 220 is configured to control the oscillation frequency in response to the flow magnitude of the input air A_in.

According to one embodiment of the invention, the air modulator

210 includes a tube member 225, which has at least one ejector opening 21 1 a, 21 1 b and 21 1 c. Each of these openings 21 1 a, 21 1 b and 21 1 c respectively connects an interior volume of the tube member 225 with the ambient air outside the vehicle 100. Furthermore, a rotatable member 220 is arranged within the interior volume of the tube member 225, which rotatable member 220 is configured to allow a varying amount of the compressed air Fp to escape through the at least one ejector opening 21 1 a,

21 1 b and 21 1 c to constitute a component of the disturbance flow F_D.

According to one embodiment of the invention, the rotatable member 220, in turn, includes at least one blocking means. Various designs of the blocking means will be discussed below with reference to Figures 4 and 5. However, in all designs the blocking means are configured to alternately cover and uncover one or more ejector openings 21 1 a, 21 1 b and/or 21 1 c when the rotatable member 220 is rotated inside the tube member 225. As a result, the intensity of the disturbance flow F_D will vary over time.

The ejector openings 21 1 a, 21 1 b and 21 1 c of the air modulator 210 may be represented by slots or holes, and are preferably arranged in an array next to one another along an essentially straight line. The shape of the ejector openings may be of circular, oval or polygon type. Each slot has a width dimension and a length dimension, where the length dimension preferably is several factors larger than the width dimension. Say the width dimension may lie in a range from approximately 0,1 mm to approximately 10 mm (more preferably 0,3-2,0 mm), and the length dimension may lie in a range from approximately 30 mm to approximately 300 mm. Moreover, the array of ejector openings are preferably positioned next to one another along an essentially straight line, which is parallel to each slot's length dimension.

Nevertheless, preferably, the air modulator 210 is configured to output oscillating air from each ejector opening 21 1 a, 21 1 b and 21 1 c in such a manner that air vortices F_D are created outside the openings. Typically, the air vortices F_D have spin axes that in proximity to the openings are essentially parallel to the essen- tially straight line along which the ejector openings 21 1 a, 21 1 b and 21 1 c are arranged. It is generally advantageous if the air modulator 210 is arranged on the vehicle 100 with the essentially straight line of the array of ejector openings 21 1 a, 21 1 b and 21 1 c oriented essentially perpendicular to a forward driving direction D_F of the vehicle 100. Here, by essentially perpendicular to the direction D_F we understand a maximum deviation of 10 degrees from 90 degrees (i.e. from 80 degrees to 100 degrees). Consequently, the spin axes of the air vortices F_D are also (at least in proximity to the ejector openings) essentially perpendicular to the direction D_F. This is a key factor in the above-mentioned perturbation of the shear layers around the vehicle 100, which reduces the global vortices behind the vehicle 100.

For example the air modulator 210 may be arranged on the ve- hide 100 with the array of ejector openings 21 1 a, 21 1 b and 21 1 c being oriented, such that the openings emit air in a main direction at an given angle, say 155 degrees, to the forward driving direction D_F. The angle of 155 degrees is not a critical measure. On the contrary, any angle in an interval from 90 degrees to 175 degrees is usable here. Namely, oscillating air vortices F_D emitted at an angle within said interval is capable of interacting efficiently with the lateral shear layers of the airflow F behind the vehicle 100.

According to one embodiment of the invention, a fan means 230 is mechanically connected with the rotatable member 220 in such a manner that a rotation of the fan means 230 causes the rotatable member 220 to rotate. Moreover, at least one conduit (here 240 and the conduits 241 , 242, 24n connected thereto) is arranged to forward the input air A_in to the fan means 230. The input air A_in cause rotation of the fan means 230, and thus also rotation of the rotatable member 220. The input air A_in, in turn, is produced as an effect of that the vehicle 100 is being propelled. Consequently, the rotatable member 220 rotates whenever the vehicle 100 moves. Specifically, since the rotatable member 220 determines the oscillation frequency of the disturbance flow F_D, there is a positive correlation between the vehicle speed and the intensity of the disturbance flow F_D.

Typically, the disturbance flow F_D exiting from the air modula- tor's 210 ejector openings 21 1 a, 21 1 b and 21 1 c will have an oscillation frequency in a range from approximately 5 Hz to approximately 500 Hz. The most desirable range is 10 - 60 Hz. According to one embodiment of the invention, a gear box may be included between the fan means 230 and the rotatable mem- ber 220 to accomplish a desired oscillation frequency relative to the vehicle speed. As mentioned above, it is further preferable if the peak-to-peak amplitude of the speed of the air exiting from each ejector opening 21 1 a, 21 1 b and 21 1 c is equivalent to approximately 0,5 time to approximately 10 times the speed of the vehicle 100.

Figure 4a shows a cross-section view of the valve means 220 of the air modulator 210 according to a first embodiment of the invention. The valve means 220 has four blocking means 221 , 222, 223 and 224 respectively, which are arranged on a central axle 226 in the tube member 225 of the air modulator 210.

The central axle 226 is rotatable, and as the axle 226 rotates the blocking means 221 , 222, 223 and 224 are configured to either cover or uncover at least one ejector opening, here exemplified by reference numeral 21 1 . Specifically, the blocking means 221 , 222, 223 and 224 are configured to cover the ejector opening 21 1 when the rotatable member 220 has a rotation angle within at least one first angular range, say 45 degrees to 60 degrees; 135 degrees to 150 degrees; 225 degrees to 240 degrees; and 315 degrees to 330 degrees respectively. Analogously, the blocking means 221 , 222, 223 and 224 are configured to uncover the ejector opening 21 1 when the rotatable member 220 has a rotation angle within at least one second angular range, say 0 degrees to 15 degrees; 90 degrees to 105 degrees; 180 degrees to 195 degrees; and 270 degrees to 285 degrees respectively. Figure 4a illustrates a situation wherein the blocking means 221 , 222, 223 and 224 are positioned such that the ejector opening 21 1 is uncovered, and thus an air flow F_D is emitted; whereas Figure 4b illustrates a situation wherein the blocking means 221 , 222, 223 and 224 are positioned such that the ejector opening 21 1 is covered, and therefore no air is emitted. For any rotation angle of the rotatable member 220 outside the above-mentioned first and second angular ranges, the ejector opening 21 1 is partially covered (i.e. in the process of being covered, or uncovered), and therefore a less than maximum air flow F_D is emitted via the ejector opening 21 1 .

Figure 4c shows a side view of the valve means 220 of the air modulator 210 according to the first embodiment of the invention. It is here apparent that each of the blocking means 221 , 222, 223 and 224 has a respective internal opening 221 ', 222', 223' and 224'. These openings 221 ', 222', 223' and 224 are configured to allow a through-passage of the compressed air F_P within the interior volume of the tube member 225. Hence, the compressed air F_P may be distributed throughout the interior volume of the tube member 225 essentially independently of how the central axle 226 and its blocking means 221 , 222, 223 and 224 is rotated. Of course, it is conceivable that less than all blocking means 221 , 222, 223 and 224 are provided with internal openings. However, this is disadvantageous because then the distribution of compressed air F_P inside the interior volume will vary more over time.

According to one embodiment of the invention, the central axle 226 to which the at least one blocking means 221 , 222, 223, 224 is attached, has an internal void configured to transport the compressed air F_P. Thereby, incoming compressed air F_P may be distributed through the central axle 226. Preferably, the central axle 226 also includes at least one opening 227, which connects the internal void of the central axle 226 with the interior volume of the tube member 225, such that compressed air F_P can pass out into the interior volume for further passage through the ejector openings 21 1 a, 21 1 b and 21 1 c.

Figure 5a shows a cross-section view of the valve means 220 of the air modulator 210 according to a second embodiment of the invention. Also here, the valve means 220 includes blocking means 521 , 522, 523 and 524 respectively, which are arranged on a central axle 226 in the tube member 225 of the air modulator 210. Naturally, although Figures 4a-b, 5a and 5c show examples of valve means 220 having four blocking means, any number of blocking means other than four is conceivable accor- ding to the invention. In the second embodiment of the invention the blocking means 521 , 522, 523 and 524 are configured to allow the compressed air F_P to flow inside the tube member 225 in parallel with a central axle 526 to which the 521 , 522, 523 and 524 are attached, see Figure 5b showing a side view of the val- ve means 220 of the air modulator 210 according to this embodiment.

The lateral passage of compressed air F_P along the axle 526 is enabled by the blocking means 521 , 522, 523 and 524 being provided with internal openings to allow such a through-passage of the compressed air F_P. Hence, the blocking means 521 , 522, 523 and 524 may be configured, as illustrated in Figure 5c, with skeletal-type of connection members between the blocking means 521 , 522, 523 and 524 and the central axle 526. The term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components. However, the term does not preclude the presence or addition of one or more additional features, integers, steps or components or groups thereof.

The invention is not restricted to the described embodiments in the figures, but may be varied freely within the scope of the claims.

Claims

1 . An airflow control system for assembly on a ground vehicle (100) in order to influence an airflow (F) around the vehicle (100), such that when the vehicle (100) travels at a particular speed the drag on the vehicle (100) is lower than if the vehicle (100) had traveled at this speed without the system, the system comprising: at least one air intake (241 ', 242', 24n', 251 ') adapted to receive input air (A_in) via an external surface of the vehicle (100), and an air modulator (210) configured to produce a disturbance flow (F_D) influencing the airflow (F) around the vehicle (100), the disturbance flow (F_D) having an intensity which varies with an oscillation frequency, characterized i n that the air modulator (210) comprises a valve means (220) controllable by the input air (A_in), the valve means (220) being configured to control the oscillation frequency in response to a flow magnitude of the input air (A_in).

2. The airflow control system according to claim 1 , compri- sing a pressurizing means (250) configured to receive ambient air from outside the vehicle (100) and supply compressed air (Fp) to the air modulator (210); the air modulator (210) being configured to produce the disturbance flow (F_D) based on the compressed air (F_P).

3. The airflow control system according to claim 2, wherein the pressurizing means (250) is configured to receive input air (A_in) via an external surface of the vehicle (100), and the air modulator (210) is configured to produce the disturbance flow (F_D) such that a maximum magnitude thereof depends on the flow magnitude of the input air (A_in).

4. The airflow control system according to claim 3, wherein the pressurizing means (250) comprises a compressor (260) configured to receive the input air (A_in) and in response thereto produce the compressed air (F_P).

5. The airflow control system according to any one of the claims 2 to 4, wherein the air modulator (210) comprises a tube member (225) having at least one ejector opening (21 1 a, 21 1 b, 21 1 c) to an interior volume thereof; a rotatable member (220) being arranged within the interior volume and configured to allow a varying amount of the compressed air (F_P) to escape through the at least one ejector opening (21 1 a, 21 1 b, 21 1 c) to constitute a component of the disturbance flow (F_D).

6. The airflow control system according to claim 5, wherein the rotatable member (220) comprises at least one blocking means (221 , 222, 223, 224), the at least one blocking means (221 , 222, 223, 224) being configured to: cover one of the at least one ejector opening (21 1 a, 21 1 b,

21 1 c) when the rotatable member (220) has a rotation angle within at least one first angular range, and uncover said at least one ejector opening (21 1 a, 21 1 b, 21 1 c) when the rotatable member (220) has a rotation angle wi- thin at least one second angular range.

7. The airflow control system according to claim 6, wherein the at least one blocking means (221 , 222, 223, 224) has at least one internal opening (221 ', 222', 223', 224') configured to allow a through-passage of the compressed air (F_P) within the interior volume of the tube member (225).

8. The airflow control system according to any one of the claims 6 or 7, wherein the rotatable member (220) comprises a central axle (226) to which the at least one blocking means (221 , 222, 223, 224) is attached, the central axle (226) having an internal void configured to transport the compressed air (F_P).

9. The airflow control system according to claim 8, wherein the central axle (226) comprises at least one opening (227) connecting the internal void of the central axle (226) with the interior volume of the tube member (225).

10. The airflow control system according to claim 7, wherein the at least one blocking means (521 , 522, 523, 524) is configured to allow the compressed air (F_P) to flow inside the tube member (225) in parallel with a central axle (526) to which the at least one blocking means (521 , 522, 523, 524) is attached.

1 1 . The airflow control system according to any one of the claims 5 to 10, wherein the system comprises: a fan means (230) mechanically connected with the rotat- able member (220) so as to cause rotation thereof in response to a rotation of the fan means (230), and at least one conduit (240, 241 , 242, 24n) arranged to forward the input air (A_in) to the fan means (230) so as to cause rotation thereof when the vehicle (100) is propelled.

12. The airflow control system according to claim 1 1 wherein the system comprises a gear box connecting the fan means (230) to the rotatable member (220).

13. A ground vehicle (100) having a body with an outer surface comprising a general front surface (1 10), a main upper surface (120), a bottom surface (1 15), two side surfaces and a rear surface (140), characterized i n that the vehicle (100) compri- ses at least one airflow control system according to any one of the claims 1 - 12, where the air modulator (210) of each of the at least one system is arranged on the vehicle (100) such that when the vehicle (100) travels at a particular speed an amount of vortex shedding behind the rear surface (140) is lower than if the vehicle (100) had traveled at this speed without the at least one system.

14. The ground vehicle (100) according to claim 13, wherein the at least one air modulator (210) is arranged such that each of the at least one ejector opening (21 1 a, 21 1 b, 21 1 c) of thereof is located downstream of a flow separation line (FSL) at which flow separation had occurred during propulsion of the vehicle (100) if no disturbance flow (F₀) had been produced.

15. The ground vehicle (100) according to any one of the claims 13 or 14, wherein at least one of the at least one air modulator (210) is arranged on at least one of the main upper surface (120), the bottom surface (1 15), the side surfaces and the rear surface (140).

16. The ground vehicle (100) according to any one of the claims 13 to 15, wherein at least one air intake (241 ', 251 ') of the at least one airflow control system is arranged on the gene- ral front surface (1 10) of the vehicle (100).

17. The ground vehicle (100) according to any one of the claims 13 to 16, wherein at least one air intake (251 ') of the at least one airflow control system is arranged in a high-pressure zone on the vehicle's (100) body in proximity to which high-pres- sure zone during propulsion of the vehicle (100) an air pressure is developed that substantially exceeds the atmospheric pressure level.