Patent Publication Number: US-2022221317-A1

Title: Fluid sensor

Description:
The present invention relates to a fluid sensor and a method of sensing fluid flow. 
     It is known from the applicant&#39;s earlier application WO 2015/059085 to provide a fluid flow sensor comprising a blister, projecting from a surface into local fluid flow, and which is provided with fluid pressure ports adjacent to the blister. The blister modifies local fluid dynamics, and characteristics of the fluid flow can be determined from the fluid pressure data obtained at the pressure ports. 
     According to a first aspect of the invention, there is provided a fluid sensor for measuring the pressure of a fluid, the fluid sensor comprising: a surface; a recess formed at the surface, the recess being configured to affect the pressure of the fluid flowing at the recess, at least one ambient sensor port for measuring ambient fluid pressure at the surface, at least one recess sensor port for measuring the fluid pressure at the recess. 
     As such the provision of a fluid data sensor having a projecting component can be avoided. Avoiding the provision of such a projecting component can tend to reduce the chance of damage to the sensor e.g. during maintenance. The drag that the sensor generates can also tend to be reduced. 
     The fluid sensor may comprise a first recess sensor and a second recess sensor. 
     Providing two recess sensors can provide some redundancy, for example if one recess sensor malfunctions. Further, the provision of two sensors can, if both are working, provide for greater resolution of information and/or smoothing of information (e.g. by averaging of measurements). 
     The recess may define a longitudinal axis, the longitudinal axis thereby defining a first side of the recess and a second side of the recess, and wherein the first recess sensor is located on the first side of the axis and the second recess sensor is located on the second side of the axis. 
     The first and second recess sensors may be offset laterally from the longitudinal axis by the same amount. 
     The recess may have a wider aspect at a first end and taper to a narrower aspect at a second end. 
     Such a provision can tend to encourage high pressure areas within the recess which can be used to generate a stronger signal (e.g. a better signal to noise ratio) from which to infer characteristics about fluid velocity. The tapering may in particular be along the principal direction of expected flow. 
     The wider aspect and the narrower aspect may be connected by a first side wall, a floor, and a second side wall. 
     At least one further recess sensor port may be provided in the first or second side wall. 
     The recess may taper gradually between the wider and narrower aspect. 
     The recess may have a maximum depth between the wider and narrower aspect. 
     The recess depth may develop gradually between the wider and narrower aspect. 
     As such the recess can tend to deter flow separation and so provide readily interpreted data. If the recess were within a turbulent flow region, data may be less readily interpreted. 
     The fluid sensor according may further comprise: a transducer at each of the respective sensor ports for converting the detected fluid pressure into a fluid pressure signal; a processor operably connected to each of the transducers and configured to receive the fluid pressure signal from each transducer, generate from the fluid pressure signals a fluid pressure profile, determine, using the fluid pressure profile, at least one characteristic of the fluid. 
     According to a second aspect of the invention there is provided a method of sensing fluid flow comprising: providing a fluid sensor, the fluid sensor comprising: a surface; a recess formed at the surface, the recess being configured to affect the pressure of the fluid flowing at the recess; at least one ambient sensor port for measuring ambient fluid pressure at the surface; at least one recess sensor port for measuring the fluid pressure at the recess, exposing the fluid sensor to fluid flow, detecting the fluid pressure at each of the ambient sensor port and the recess sensor port to determine a fluid pressure profile, acquiring a relationship between fluid pressure profiles and a predetermined fluid characteristic, applying the relationship to the fluid pressure profile to determine the predetermined fluid characteristic. 
     Acquiring a relationship between the fluid pressure profiles and the predetermined fluid characteristic may comprise acquiring a look up table mapping fluid pressure profiles to predetermined fluid characteristics. 
     Acquiring a relationship between the fluid pressure profiles and the predetermined fluid characteristic may comprise establishing a predictive algorithm. 
     The predetermined fluid characteristic may be the fluid velocity at the surface of the sensor. 
    
    
     
       So that the invention may be well understood at least one embodiment thereof will be described below, with reference to the following figures of which: 
         FIG. 1  shows a three-dimensional representation of a fluid sensor; 
         FIG. 2  shows an elevation representation of the fluid sensor of  FIG. 1 ; 
         FIG. 3 a    shows a cross sectional view of the fluid sensor of  FIG. 1 , along a longitudinal axis; 
         FIG. 3 b    shows a cross sectional view of the fluid sensor of  FIG. 1 , along a lateral axis; 
         FIG. 4  shows a three-dimensional representation of a further fluid sensor; 
         FIG. 5  shows a cross sectional view of the fluid sensor of  FIG. 4  along a longitudinal axis; 
         FIG. 6  shows three-dimensional representation of a still further fluid sensor; 
         FIG. 7  shows a cross sectional view of the fluid sensor of  FIG. 6  along a longitudinal axis; 
         FIG. 8  shows a flow diagram setting out a method of sensing a fluid; and 
         FIG. 9  shows diagrammatically an aircraft comprising air sensors. 
     
    
    
     Referring to  FIGS. 1, 2, 3   a  and  3   b  there is shown a first fluid sensor  100  comprising a surface  102 , a recess  104 , an ambient sensor port  106  and recess sensor ports  108 . 
     The surface  102  may be part of the outer skin of a body, vehicle or platform. The surface  102  is a planar surface; however variant surfaces are contemplated that need not be planar. 
     The fluid sensor  100  is substantially symmetrical, having a similar first  110  and second  120  side, and thereby defines a longitudinal axis X about which it is symmetrical. (Alternative embodiments are envisaged which would not need to be symmetrical). 
     The rim of the recess  104  comprises a leading edge  101 , a trailing edge  103  and two side edges  105 ,  107 . These edges together generally define a funnel shape. 
     The recess  104  is defined by a first side wall  118 , a floor  120  and a second side wall  122 . 
     The floor  120  extends from both the leading edge  101  and the trailing edge  103  to a maximum depth section  132 . Further, the floor  120  extends to the base of each of the first and second side walls  118 ,  122 . 
     The floor comprises a down-ramp section  130  interconnecting the leading edge  101  with the maximum depth section  132 . The floor  120  comprises an up-ramp section  134  interconnecting the maximum depth section  132  with the trailing edge  103 . The longitudinal aspect of the down-ramp section  130  is approximately equal to the longitudinal aspect of the up-ramp section  134 , thereby locating the maximum depth section  132  at the longitudinal centre of the sensor. (As shown, the maximum depth section  132  is approximately a quarter the length of the down-ramp or up-ramp section, longitudinally. Thus it occupies a central ‘ninth’ (approximately 10%) of the longitudinal aspect of the sensor. However, in other embodiments the maximum depth section may be wider, occupying a central 10-30%). 
     The leading edge  101  is wider than the trailing edge  103 . In the present sensor, the leading edge  101  is approximately four times wider than the trailing edge  103 . 
     The side walls  118  and  122  extend from the surface  102  at the side edges  105  and  107  respectively at an angle α configured to balance sensing performance (in particular to maximise the pressure effect) and minimisation of flow separation (in particular the avoidance of flow separation altogether). Accordingly the angle may be approximately 45 degrees. (In variants on this embodiment, the angle α may be any angle between 30 and 60 degrees). Each of the side walls  118  and  122  abut the floor  120  at their respective bases. 
     Each side edge  105 ,  107  is curved with a single point of inflection  124  approximately at its midpoint. Accordingly each side edge defines an S-curve. The curvature is such that the offset between the wall and the axis reduces increasingly going from the leading edge  101  to the point of inflection  124  but reduces decreasingly going from the point of inflection  124  to the trailing edge  103 . 
     Thus the recess provides a smoothly tapered channel through which fluid can flow with reduced chance of boundary layer separation occurring, whilst tending to provide certain areas within the recess where fluid pressure will be higher compared to the surface. 
     To measure the ambient pressure, the ambient sensor port  106  is positioned at the leading edge  101  and on the longitudinal axis. 
     To measure the higher pressure in the recess  104 , the recess sensor ports  108  are provided at the maximum depth section  132  of the floor  120 . In the present sensor, two recess ports are provided and these are offset laterally in opposite directions from the longitudinal axis by a distance o 1  and o 2 . Here o 1  and o 2  are substantially equal. 
     Referring particularly to  FIG. 3 a   , for each sensor port  106 ,  108  there is further provided a transducer  126 . The transducers  126  are operably connected to a processor  128 . 
     Each transducer  126  is arranged at its respective sensor port such that it may detect the fluid pressure at the port and convert that into a fluid pressure signal for passing to the processor  128 . 
     As shown in  FIG. 3 a   , the transducers  126  are located at the mouth of the ports  108 ; however, in alternative embodiments, the transducers  126  may be remote from the mouth of the ports  108  and in communication therewith by way of an interconnecting channel. 
     Referring to  FIGS. 4 and 5 , a second fluid sensor  200  is shown. This fluid sensor is broadly similar to the first fluid sensor  100  and so for clarity not all components are discussed or provided with a reference numeral. Where reference numerals are provided in respect of a component which is comparable to one in the first fluid sensor  100 , the reference numeral may be incremented by 100. 
     The second fluid sensor  200  comprises a recess  204  which is defined by a floor  220  and a pair of side walls  218  and  222 . 
     The floor comprises a down-ramp  230  and an up-ramp  234  section where the down-ramp  230  has a greater longitudinal aspect than the up-ramp  234  section. 
     Each side wall extends from a respective side edge  205  or  207 . The side edges are substantially straight lines and as such, the side walls taper gradually but are not curved. 
     As such the rim of the recess  204  generally defines a trapezoidal shape. 
     A single ambient port  206  is provided at the leading edge and on the longitudinal axis X. 
     A single recess port  208  is provided at the maximum depth section of recess  204  and the longitudinal axis X. 
     Referring to  FIGS. 6 and 7 , a third fluid sensor  300  is shown. This fluid sensor is broadly similar to the first and second fluid sensors  100 ,  200  and so for clarity not all components are discussed or provided with a reference numeral. Where reference numerals are provided in respect of a component which is comparable to one in the first fluid sensor  100 , the reference numeral may be incremented by 200. 
     The third fluid sensor  300  defines a recess  304  which has a rim in the general shape of a filleted equilateral triangle. 
     The recess  304  is defined by a single curved floor surface  320  which extends down from the rim at surface  302  to a maximum depth. To aid with understanding of this surface, dashed lines are provided in  FIG. 6 . 
     The fluid sensor  300  comprises an ambient port  306  (at a leading edge of the rim) and three recess ports  308   a ,  308   b . The central sensor port  308   a  is positioned at a region of maximum depth and on the longitudinal axis X. The lateral sensor ports  308   b  are positioned at an intermediate depth and are offset from the longitudinal axis X by an equal and opposite amount along the lateral axis Y passing through the sensor port  308   a.    
     In operation, and referring to  FIG. 8 , a fluid sensor (for example  100 ,  200  or  300 ) is provided at step S 2  and exposed to a fluid flow at step S 4 . 
     Then at generalised step S 6 , the fluid pressure profile can be determined. More particularly, the fluid pressure at the ports can at step S 8  be measured (using for example the transducers  126  and the processor  128 ) and consolidated at step S 10  to provide an overall fluid pressure profile for the fluid sensor. The fluid pressure profile is a time-variant signal. 
     Once obtained, the fluid pressure profile can be used at step S 12  to infer certain characteristics of the fluid flow by reference to a previously-acquired relationship between the fluid pressure profile (for the particular fluid sensor) and a predetermined characteristic (generalised step S 5 ). 
     More particularly, the relationship is acquired by at step S 7  previously having obtained data for known pressure profile and known values of the certain fluid characteristics, and then at step S 9  having used that data has to populate a look up table. 
     However, in alternative embodiments, instead of using a look up table to determine the relationship between pressure profiles and values of the fluid characteristics, a predictive algorithm may be used. Such a predictive algorithm can be a neural network which has been trained, using the known data, to map pressure profiles onto fluid characteristics. 
     It is contemplated that various predetermined characteristics of the fluid flow may be inferred using this approach. In particular, the fluid velocity and the fluid direction at the surface may be the predetermined characteristic determined in this way. 
     Referring to  FIG. 9  there is shown an aircraft  400 . 
     The aircraft  400  is in the general form of a jet aircraft and defines an aircraft longitudinal axis  440 . 
     The aircraft  400  comprises a wing structure made up of a starboard wing  402  and port wing  404 . The portion of the aircraft  400  forwards of the wing structure is referred to as the forebody  406 . The portion of the aircraft backwards of the forebody is referred to as the afterbody  408 . The aircraft  400  is clad at its outer surfaces in a skin  401 . 
     The aircraft  400  further comprises a first recessed fluid sensor  410  and a second recessed fluid sensor  412 . Each of the sensors  410 ,  412  is formed by a recess in the skin  401  of the aircraft  400 . Each recess is distinct from the overall topography of the skin, which may be planar in proximity to the recess or may be arcuate or otherwise contoured in proximity to the recess. 
     The fluid sensors  410 ,  412  are substantially similar to the fluid sensor  100 , and are configured for sensing air (fluid sensors substantially similar to for example sensor  200  or  300  may be used in alternative embodiments). As such each of air sensors  410  and  412  comprise a port at the main skin topography (e.g. at the leading rim edge of the recess) and two ports within the respective recess. Associated with each of these ports is a respective transducer for generating an electrical signal representative of air pressure. 
     The first air sensor  410  is located on the port-side of the forebody  406 , the second air sensor  412  is located on the underside of the forebody  406 . A further air sensor (not shown) may be provided on the starboard-side of the forebody  406 . The first air sensor  410  and second air sensor  412  comprise recesses having substantially the same form as fluid sensor  100 . 
     The air sensors are located on the forebody such that the flow axis  415  they define (for example the flow axis  415  defined by the first air sensor  410 , which is substantially equivalent to the longitudinal axis X of the fluid sensor  100 ) is generally aligned with the longitudinal axis  440  of the aircraft  400 . This alignment may for example arise from the flow axis  415  being parallel with the longitudinal axis  440 . 
     Still further, the aircraft  400  comprises a central processor  428  which receives as input from each of the air sensors  410  and  412  the electrical signals representative of pressure at their respective ports. 
     The processor  428  is configured to determine from these inputs certain characteristics of the air flow at the aircraft. 
     For example, the processor  428  is able to determine the local airspeed and the local direction of air flow for each sensor. This determination may be made by reference to an established data set (for example provided in the form of a look up table correlating pressure profiles with fluid characteristics). 
     With air pressure, airspeed and air direction determined for each sensor, the processor  428  may be further configured to determine aircraft characteristics such as pressure altitude, angle of attack and sideslip. 
     The aircraft  400  further comprises a pitot tube  414  at the foremost point which may also feed a signal representative of pressure into the central processor  428  for use in further corroborating results. The provision of a pitot tube enables further pressure data to be collected; however alternative embodiments do not comprise a pitot tube, and sufficient air pressure data can be collected from only the air sensors  410 ,  412 . 
     The processor  428  is further connected to a display  420  in the cockpit  422  so that the determinations of the processor  428  can be displayed to a pilot in a human-readable format. 
     In operation, with the aircraft in flight (for example any of the phases of flight including take off, climb, cruise, descent and landing), air will flow over the forebody and through the channels defined by the recessed air sensors  410  and  412 . 
     Whilst flowing through the air sensors  410 ,  412 , the air will impinge on the pressure sensor ports and give rise to the generation of air pressure data at the respective transducers. 
     The air pressure data from each of the transducers is relayed to the central computer  428  where it can be processed to determine an air pressure profile for each of the air sensors  410 ,  412 . 
     From the sensor-specific air pressure profile, values of certain flow characteristic can be determined. For example the air velocity at each air sensor  410 ,  412  may be determined. 
     Alternatively or additionally, if two or more recess ports are provided at each air sensor, then air flow direction for such an air sensor can be determined. 
     Moreover, with air pressure profiles provided for two or more separate air sensors  410 ,  412 , information about flight characteristics (e.g. angle of attack, sideslip) can be determined at the central processor. 
     Further, with two or more pressure profiles obtained from separate sensors  410 ,  412 , an average of the values could be taken. The average may be the mean, mode or median. 
     Still further, if three recessed air sensors or more are provided, then any outlying data can be identified and ignored, for example by majority voting. Thus an aircraft  400  provided with not only air sensor  410 ,  412  but also a further air sensor on the starboard-side (not shown), can compare air pressure profiles so that any outliers in the readings will become apparent. 
     Thus, where two or more air sensors are provided then not only does that lead to a higher resolution understanding of air flow at the forebody, but also steps can be taken to smooth out the results from any error-prone or malfunctioning air sensor. 
     In addition to the embodiments explicitly discussed above, the skilled person would be able to readily understand further inventions within the scope of the present disclosure. Such inventions could combine features from the above embodiments. 
     Other variants would also be within the scope of the invention such as: the provision of a surface which is not necessarily planar, but could be curved or faceted; the provision of a non-symmetrical recess; a greater number of ports could be provided as an array for more resolution in determining the pressure profile; and the topography of the recess need not be configured for fluid flow from a particular direction, and instead could be configured to determine fluid flow from any direction, in such variants, the recess may have a rotational symmetry and be absent a taper. 
     The surface and the recess may be fabricated from a smooth skin material that is substantially non-porous and suitable for forming into the relevant three dimensional shaped. For example the surface and the recess may be formed from a metal, optionally coated with a paint.