Air-pressure sensor

Details Air-pressure sensor Air-pressure sensor

2001-01-08

2003-05-06

Noori, Max (Department: 2855)

Measuring and testing

Volume or rate of flow

Using differential pressure

Reexamination Certificate

active

06557423

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to determining flight parameters of the aircraft, or to other science and technology fields where fluid and gas flows are involved.
2. Description of the Related Art
Measurement of flow parameters is one of the most important concerns of atmospheric flight mechanics and aerodynamics of the aircraft. Presently, for measuring of flight (flow) parameters used are air-pressure heads (APH) frequently mounted directly on aircraft fuselage or any other component thereof, which heads measure actual parameters of a local flow approximating a planar flow. The aircraft are generally fitted with a plurality of such APH's that measure local parameters of a flow. True flight parameters are determined on the basis of calibrations carried out beforehand. Measuring of flight parameters is a very important task for high-maneuverability airplanes in view of the substantially broadened in-flight angles of attack and a wide range of flight speeds (from slow subsonic speeds to those that far exceed the supersonic speed). This task is rather important for helicopters in connection with their high maneuvering capabilities (i.e., forward or backward, to the right or left, upward or downward flights) and automation of these flight modes using the data obtained from a flight parameter measurement system.
Known is an air-pressure head, comprising a housing in the form of a round cylindrical rod having intake orifices arranged around the cross-section circumference and connected via ducts to nipples (Petounin A. N., Metody—Techniques and Equipment for Measuring the Gas Flow Parameters), M., Machinostroyeniye publishers, 1972, pp. 88-100, FIG. 1.102; Glaznev V. N., Zavaroukhin S. G., Experimental Investigation of Planar and Axially Symmetrical Vortex Flows using a Cylindrical Sensor in a Wide Numeric Range, M., Proceeding of Central Institute for Aerohydrodynamics, vol. 14, N 4, 1983). Flow parameters are determined using said head by measuring the pressures occurring at the windward side of the head in the area of continuous flow according to the calibration relationships that enlink the determined parameters with the measured pressures.
The disadvantages of the APH of the above-discussed type are as follows:
the impossibility of measuring static pressure to an acceptable accuracy in the range of M values from 0.8 to 1.1 due to the known phenomenon of the transonic stabilization;
the impossibility of using, for determining the flow parameters, the inlet orifices disposed at the leeward side in the head's separating flow zone, in which orifices the pressures, though not being subjected to the transonic stabilization effect, strongly depend on Reynolds number, roughness of the surface and turbulence level of the incoming flow;
still another disadvantage, being actually a result of the preceding disadvantage, consists of a significantly excessive number of pressure measuring ducts. For determining three parameters (total pressure P
1
, static pressure P
s
and downwash angle &agr;) this APH requires such to be provided with at least three orifices at the windward side in the separation-free zone. Rough estimates demonstrate that when the flow parameters are to be determined within the range of &agr;=0÷360°. For acceptable sensitivity being maintained, at least 8 to 9 inlet orifices, that are equally spaced (the pitch being 45° or 40°) around the APH cross-section circumference, are required, which results in greater dimensions of an APH, its increased aerodynamic drag, greater weight of structure of an APH itself and also that of measuring instruments, because a pressure sensor must be connected to each of the ducts. Further, this results in a more expensive measuring system based on such APH's.
Known is a device (Europaische Patentschrift, Veroffentlichungsnummer, 0049756 B1, G 01 F 1/46, G 01 L 13/00, Vorrichtung zum Messen des Differenzdruckes; prioritaet: 09.10.80 DE 3038180, Patentinhaber; IWK Regier and Kompensatoren GmbH: Erfinder: Fehbr, Dieter, Dr., Dipl-Phys.) adapted to measure a pressure drop. The basic element of this device is a rod in the form of regular hexagonal prism having on one of its edges an orifice (or a plurality of orifices connected to pneumatic ducts) intended for pressure measuring. When the rod in a flow is oriented such that the flow velocity vector extends through the edge that has an opening, the rod axis and the opposite edge, the pressure approximating the total pressure is sensed using a pressure sensor connected via a pneumatic duct to said orifice(s). When the rod in a flow is oriented such that the orifices thereon are deployed with respect to the velocity vector at 180°, the base pressure can be determined using these orifices. Thus, using APH's of this type, the flow strength (or total P
t
and static P
s
pressures) can be measured on the basis of the preset calibrations. Said patent proposes the devices consisting of two rods oriented as described above and intended to measure P
t
and P
2
is gas conduits.
BRIEF SUMMARY OF THE INVENTION
However, such APH, or a device based thereon, are not suitable intrinsically to measure three flow parameters at a time (total pressure P
t
, static pressure P
s
and angle of downwash (attack) &agr;) for it lacks the appropriate number of orifices, at least three orifices, for intake of pressures. Actually, the flow parameters are known to be determined on the basis of predetermined relationships between pressures P
i
and angle of attack (downwash) &agr; of an undisturbed flow, total P
t
and static P
s
pressures of an undisturbed flow:
P
i
=f
i
(&agr;,
P
t
, P
s
),  (1)
measured in an air-pressure head in i number of points of pressure intake. For resolving this system of equations with respect to &agr;, P
t
, P
s
, it is required to have i≦3 orifices, and, further, such system of equations must be sufficiently well-posed. For example, when two orifices i=1 and i=2 are located in the separation zone where the pressure is equalized, then P
1
≈P
2
will be effective in a broad range of &agr;′, and the system becomes ill-posed or unresolvable. Hence, when it is required to measure parameters of a plane-parallel stream within the range of &agr;=0÷360°, the APH body must have, as the analysis of the experimental data demonstrates, i≦4 orifices, and they are to be distributed such that to perform <<switching>> from some orifices to another ones.
Another disadvantage of the mentioned prior art is the circumstance that the pressure intake orifices are disposed on a prism edge. This results in that even in a slight re-orienting of such APH relative to the flow (the position as discussed above), a flow separates from that edge. This results in a loss of sensitivity to a change in &agr;, i.e. said system of equations (1) becomes unresolvable.
The most pertinent art is an air-pressure head implemented in the form of a rod having cross-section of equilateral triangle. On the rod end face, on the axis common with said rod, positioned is a cylindrical superstructure having cross-section in the form of equilateral triangle whose sides are equal to those of the rod cross-section, said triangle being slewed with respect to the rod cross-section by angle &phgr;=60°. On facets of the rod and superstructure, implemented are six inlet orifices connected via ducts to nipples (Golovkin M. A., Yefremov A. A., Priyomnik vozdoushnogo davleniya, [An Air-Pressure Head], Patent of the RF N 1809341, priority as of Apr. 8, 1991).
The disadvantages of that APH are as follows:
complexity of design;
insufficient accuracy in determining flight parameters, particularly in case of sliding;
an excessive number of pressure-measurement ducts, which circumstance results in a greater weight of an APH itself and a measuring system as a whole.
The object of the invention is to simplify the design, to improve the accuracy of measurement of flight (flow) parameters, and to redu

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