SU1171679A1 - Passage-type static-pressure probe - Google Patents

Abstract

FLOW STATIC PRESSURE RECEIVER, comprising a cylindrical housing with an inlet confuser and an outlet diffuser, inside of which are receiving openings, characterized in that the confuser is divided into two in order to increase the accuracy of pressure selection. parts that are interconnected by a cylindrical section, with receiving holes in the middle part of the cylindrical section, and its diameter D and length L are chosen from the condition D (I, 40-l, 45) d and L

Description

The invention relates to the field of measurement technology, in particular, to means of measuring static pressure, and can be used on helicopters and vertically taking off devices, in gauges of barometric altitude, vertical speed and airspeed, where information about static pressure is required.

The aim of the invention is to improve the accuracy of the selection of static pressures by reducing the sensitivity to changes in flow velocity.

FIG. 1 shows the design of a static pressure flow receiver; in fig. 2 — graphs of perception errors of static pressure versus flow rate of receivers of various designs.

The cylindrical receiver body 1 has an inlet confuser, made of two parts 2 and 3, which are interconnected by a cylindrical section 4 with apertures 5 for sampling static pressure. The second part 3 of the confuser with its smaller diameter 6 is coupled with the diffuser 7 at the receiver output.

The work of the receiver is as follows.

The incoming air flow from the side of the confuser 1 partially decelerates, and as a result, the pressure at the inlet of the confuser becomes more static. As the confuser is narrowed, the air flow accelerates and in the narrow part of the receiver the air flow rate reaches maximum values. The pressure in the narrow part of the receiver becomes less static. The selection of the pressure of the moving air flow, equal to the static pressure of the undisturbed flow, is made by means of the holes 5 in the cylindrical section 4, which divides the confuser of the receiver into two parts 2 and 3.

If we denote by V the flow rate in the cylindrical part of the receiver, through Vtx the velocity at the entrance to the receiver, through Rscc, the pressure corresponding to this velocity, then the Bernoulli equation relating the specified gas flow parameters will be written

p 4- - p 4- p VM

(About 2 in -

where p is the flux density.

Since a pressure head is formed in front of the receiver input, the speed of the VBX inlet to the receiver is less than the flow rate V, and the pressure at the inlet P is greater than the free flow pressure P by the value of D P.

From the expression (1) the differential pressure of the DR will be equal to

lt

Yau

PB, - P

(2)

2

This difference can also be determined through the pressure in the narrow part of the receiver and the coefficient of resistance of the receiver.

AR p f-,

(3)

where is the flow rate in the narrow part of the receiver. From expressions (2) and (3) we have

(four)

Drawing to the obtained expression (4) the equation of the continuity of the jet, written through the parameters of the input, cylindrical and narrow sections of the receiver SrV S ,, Vy, S "-Ve

exVax

-im

r + nji

(6)

Zuz

where t is SBX;

Syi Sys - consistently square inlet, cylindrical

and narrow receiver sections.

It was established experimentally that for the angles of narrowing of confuser c (j ± 40-65 °, otj 8-10 ° is

  -0.48-0.51

  -0.48-0.51 (7)

and at the same time, the greatest effect is achieved if the length of the cylindrical section of the receiver L and the diameter of a narrow section d are in the ratio L (0.3-0.6) d. The ratios obtained relate to receivers, in which the length of the confuser part LI is f L; (without taking into account the length of the cylindrical part) is equal to the diameter of the narrow part of the receiver (with m 0.3-0.4), and the selection of static pressure is carried out through the holes from the qiq of the lindrical section located close to its middle.

Taking into account (6) and (7) and the fact that

d ..

ratio for diaD

m

meter cylindrical section and the diameter of the narrow part of the receiver D (l, 4-l, 45) d (8). FIG. 2 shows the curves characterizing the perception error value of the 4P static pressure,% depending on the flow velocity, of which curve A corresponds to the well-known receiver with confusor and cylindrical flow part (1), curve B - flow receiver with confusor and diffuser (2) , and curve B - to the proposed receiver. As follows from the graph, the accuracy of the perception of static pressure by such a receiver is more than ten times higher than the accuracy of the known flow receivers. i-O.I

vr FIG. 2

Claims (1)

FLOW RECEIVER OF STATIC PRESSURE, - containing a cylindrical body with a confuser at the inlet and a diffuser at the outlet, inside which there are receiving holes, characterized in that, in order to increase the accuracy of pressure selection by reducing sensitivity to changes in flow velocity, the confuser is divided into two parts that are interconnected by a cylindrical section, while the receiving holes are made in the middle part of the cylindrical section, and its diameter D and length L are selected from the condition D = (1.40–1.45) d and L = (0.3– 0.6) d, where d diameter and converger cone pairing.