RU2561784C1 - Method of measurements of mach number in aerodynamic pipe - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: several times in the aerodynamic pipe single registration of pressure transmitter signals is performed, and Mach number is determined using these signals. At fixed speed of the air flow in the aerodynamic pipe the moment of stop of the registration of the pressure transmitter signals is determined by check of these signals being within the tolerances corresponding to the measured Mach number. These operations are separated to two processes synchronous in time. Equations for tolerances determination are provided.

EFFECT: Mach number measurement with required accuracy for minimum possible time of operation of the aerodynamic pipe.

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Description

The invention relates to the field of measuring equipment and is intended for measurement under conditions of uneven and unsteady air flow in the working part of the wind tunnel of the Mach number during certification of wind tunnels, obtaining aerodynamic characteristics of test models for their subsequent use in certification of algorithms and programs providing calculation of aerodynamic characteristics of aircraft .

Currently, the creation of air flow in wind tunnels is associated with high material costs, therefore, the requirement to minimize the time to obtain experimental data of the required, usually high, accuracy is relevant.

и P₀ - после и до прямого скачка уплотнения, пользуясь этими сигналами определяют число Маха в аэродинамической трубе (Поуп А., Гойн К. Аэродинамические трубы больших скоростей. - М.: Мир, 1968, стр. 24, 28, 74), при этом неравномерность и нестационарность характерна не только для измеряемого числа Маха, но и для меняющихся асинхронно регистрируемых сигналов датчиков давлений.At high subsonic and supersonic speeds, the signals of the static P and full P ₀ pressure sensors are recorded; at hypersonic speeds, the braking pressure sensors are: $$P_0^{/}$$

and P ₀ - after and before the direct shock wave, using these signals determine the Mach number in the wind tunnel (Pope A., Goyn K. High-speed wind tunnels. - M .: Mir, 1968, p. 24, 28, 74), in this case, non-uniformity and non-stationarity is characteristic not only for the measured Mach number, but also for changing asynchronously recorded signals of pressure sensors.

There is a method of measuring the average Mach number, according to which, during the aerodynamic experiment, multiple signals of pressure sensors are recorded, the average Mach number is determined using these signals, and then the error of measurement of this Mach number is estimated (Petunin A.N. Methods and techniques for measuring parameters gas flow. - M.: Mechanical Engineering, 1996, p. 281-284).

However, when using this method, it is possible to measure only the average Mach number at each fixed speed of the pipe, moreover, the measurement accuracy with uneven and unsteady air flow, as a rule, is low.

There is a method of measuring the Mach number, adopted as a prototype, according to which a single registration of pressure sensor signals is carried out in a wind tunnel, using these signals, the Mach number is determined, and the error in measuring the Mach number is then estimated (Bertyn V.R., Yushkov I.I. Analysis of the accuracy of measuring the pressure head and the number M in wind tunnels at subsonic and supersonic speeds. - M .: Transactions of TsAGI, 1966, p. 5.).

However, with this method, an a posteriori estimate of the accuracy of the indirectly measured Mach number due to the irregularity and unsteadiness of the flow is often lower than required. This is followed by a repeated and not always a single launch of the wind tunnel, which leads to an increase in the duration of the aerodynamic experiment, and consequently, to an increase in its cost.

The objective of the invention is the measurement with the required accuracy of the Mach number in the conditions of uneven and unsteady air flow in the working part of the wind tunnel with minimal time spent on obtaining experimental data. The technical result is the measurement of the Mach number with an error not exceeding the specified error for the minimum possible time of the pipe.

и P₀, определение допусков P и P₀ или $$P_0^{/}$$

и P₀ на зарегистрированные сигналы, контроль попаданий зарегистрированных сигналов в допуски - повторяют до тех пор, пока сигналы датчиков давлений не попадут в допуски, после чего посылают первому процессу синхронизирующий знак о прекращении регистрации сигналов датчиков давлений.The task and the technical result are achieved by the fact that in the method of measuring the Mach number, according to which the signals of the pressure sensors are recorded once in the wind tunnel, two processes are performed simultaneously and synchronously in time. The first process — the one-time recording of pressure sensor signals — is repeated until a synchronizing sign is received from the second process to stop the registration of pressure sensor signals. The second process is the determination of the Mach number using the last recorded signals of the pressure sensors P and P ₀ or $$P_0^{/}$$

and P ₀ , the definition of tolerances P and P ₀ or $$P_0^{/}$$

and P ₀ to the registered signals, control of hits of the registered signals in tolerances - repeat until the pressure sensor signals fall into the tolerances, after which they send the first process a synchronization sign to stop the registration of pressure sensor signals.

. Допуски определяют с использованием полиномиальных зависимостей, отвечающих формулам или непосредственно по формулам:Hit control is carried out using the inequalities P ₀ ≥P ₀ and, accordingly, P≥P or $$P_0^{/}\ge P_0^{/}$$

. Tolerances are determined using polynomial dependencies corresponding to the formulas or directly by the formulas:

- for large subsonic and supersonic speeds

,

,

,

,

- for hypersonic speeds

,

,

,

,

,Where

,

,

,

- приборные погрешности датчиков давлений, Δ[M] - заданная погрешность измерения числа Маха, ω=Δ[P₀]/Δ[P], $$\varpi =\Delta \left[P_0\right]/\Delta \left[P_0^{/}\right]$$

, κ - показатель адиабаты для воздуха.Δ [P], Δ [P ₀ ], $$\Delta \left[P_0^{/}\right]$$

- instrument errors of the pressure sensors, Δ [M] is the specified error in the measurement of the Mach number, ω = Δ [P ₀ ] / Δ [P], $$\varpi =\Delta \left[P_0\right]/\Delta \left[P_0^{/}\right]$$

, κ is the adiabatic exponent for air.

The implementation of the method in the proposed manner, i.e. its implementation in the form of two processes running in parallel and synchronously in time, repeatedly providing a single registration of pressure sensor signals and then repeatedly determining the Mach number and monitoring the registration of the last recorded pressure sensor signals in the tolerances intended for them in order to stop registration pressure sensor signals, when this is no longer necessary, is not known in the measurement technique.

In FIG. 1 shows a block diagram of a device for implementing this method; in FIG. Figures 2, 3 and 4 show data obtained experimentally and experimentally that confirm the reliability and effectiveness of the results of an experimental verification of this method.

A device for implementing the method of measuring the Mach number in a wind tunnel contains pressure sensors 1, a measuring device 2, a recording device 3, which are standard components of a pneumometric system, a computing and control device 4, a common RAM 5 of devices 3 and 4 for monitoring signs synchronizing operation of these devices, and registration of signals from pressure sensors, the RAM 6 standard for the device 4.

The proposed method is implemented as follows.

Having received, for example, a message about the beginning of measurements from the automated wind tunnel control system, using the device 4, the synchronizing signs “+” and “-” are placed in the memory 5, a start message is sent to the device 3, and then the synchronizing signs are monitored. While using the device 4 recognize the signs "+" and "-", continue monitoring the signs. If the signs “-” and “+” are recognized, then using the device 4 they move from the memory 5 to the memory 6 the registered signals received from the pressure sensors, place the synchronizing signs “-” and “-” in the memory 5, process the sensor signals moved in memory 6, while determining the Mach number and tolerances for pressure, control the ingress of sensor signals into these tolerances. If the sensor signals fall within the tolerances, using the device 4 they send a message to the aforementioned automated control system about the completion of measurements and, monitoring the synchronizing signs, wait for the signs “-” and “+”, then send a stop message to the device 3. If the sensor signals are in if the tolerances didn’t fall, then, using the device 4, monitoring the synchronizing signs, wait for the signs “-” and “+”, after which they perform the above operations, starting with moving from memory 5 to memory 6 registered signals received from the pressure sensors. Using the device 3, which starts to function according to the start message received from the device 4, the signals of the pressure sensors are recorded in memory 5, the synchronizing signs “-” and “+” are placed in this memory, and then they are monitored. While using the device 3 recognize the signs "-" and "+", continue monitoring the signs. If the signs “-” and “+” are recognized, then using the device 3, the pressure sensor signals are recorded in memory 5, the synchronizing signs “-” and “+” are placed in this memory, and then they are monitored. Next, the operations performed using the device 3 are repeated until a stop message is received from the device 4.

Information about the parameters of the devices included in the implementation scheme of the method is as follows.

Devices 3 and 4 can be built using two processors of a dual-processor computer or a multi-core processor of a single-processor computer. However, it should be borne in mind that the processor used in device 4 must be several times more productive than the processor used in device 3, or the number of cores of a multi-core processor used in device 4 must be several times larger than the number of cores. used in device 3, with the same core performance. The amount of total RAM 5 should be sufficient for recording signals from pressure sensors and monitoring synchronizing signs. For synchronizing characters, you can use two bytes of memory 5 or the sign bits of the machine words of this memory allocated to the signals of the pressure sensors.

Thus, in this method of measuring the Mach number in a wind tunnel, two devices operate in parallel. When implementing this method according to the presented scheme (Fig. 1), one device, which is part of the pneumometric system, all the time performs the operation of a single registration of pressure sensor signals, the other device all the time performs, each time using the once registered signals of the pressure sensors, determining the Mach number and tolerances corresponding to this Mach number, control of the once recorded signals of pressure sensors falling into tolerances, while using the common operational amyati synchronization of the two devices, and each time the sensor signals contact pressures tolerances device, part of the pneumometric system stops recording the signal pressure sensors that minimizes the time of aerodynamic experiment. In turn, the determination of tolerances and the control of the occurrence of once recorded pressure sensor signals in these tolerances contribute to the measurement of the Mach number with the required accuracy. The implementation of this method according to the presented scheme (Fig. 1) provides a measurement of the Mach number during one start of the wind tunnel at all fixed flow rates corresponding to this start-up. In addition, this method allows you to organize a diagnostic analysis, for example, in order to identify the sensor whose signals often do not fall into tolerances.

For experimental verification of this method, the signals of the pressure sensors obtained in the wind tunnel of high subsonic speeds were used. The results of the experimental verification at Δ [M] = 0.001 and Mach numbers from 0.6 to 1.0 are presented in FIG. 2. The solid curves in FIG. Figure 2 shows the tolerances that correspond to the formulas for large subsonic and supersonic speeds. Dotted curves interpolate pressure sensors that have successfully passed control. In FIG. 3 is a close-up fragment of FIG. 2 for Mach numbers from 0.825 to 0.950: solid and dashed curves corresponding to total pressure. In the same place, the upper and lower boundaries of the dispersion of the signals of the full pressure sensor with uneven and unsteady air flow are shown by dot-and-dot curves. To construct these boundaries, we used repeatedly recorded sensor signals. As shown in FIG. 4, in the presence of an uneven and unsteady flow, the scattering intervals of the signals of the sensors of full and static pressure significantly exceed the instrumental errors of these sensors at almost all Mach numbers.

Formulas for determining tolerances are obtained using theoretical dependences (Applied Gas Dynamics / Ed. By S. A. Khristianovich. - M.: TsAGI Publishing House, 1948, p. 71, 73; I. Yushkov. Analysis of Random Errors of Measurement of Flow Parameters in wind tunnels at high supersonic speeds. - M .: Proceedings of TsAGI, issue 856, 1962, p. 5.) connecting the Mach number with the signals of pressure sensors at high subsonic and supersonic speeds

and at hypersonic speeds

The following relations were also used (I. Yushkov, I. Analysis of random errors in measuring flow parameters in wind tunnels at high supersonic speeds. - M .: Transactions of TsAGI, issue 856, 1962, p. 10, 13; Petunin AN Methods and technique measurements of gas flow parameters. - M.: Mashinostroenie, 1996. - pp. 304, 305) between the errors in the measurement of the Mach number and the instrument errors in the pressure sensors.

The formulas for determining the tolerances at high subsonic and supersonic speeds are obtained as follows. Having represented the dependence (1) in the form of the function P ₀ = f ₀ (P, M, κ), we replace it with the value P ₀ in relation (3). Using algebraic transformations, we reduce the latter to the form P = φ (M, κ, ω, Δ [P], Δ [M]). Dependence (1), presented in the form of the function P = f (P ₀ , M, κ), is used to bring relation (3) to the form P ₀ = ψ (M, κ, ω, Δ [P ₀ ], Δ [M ]). Similarly, using dependence (2) and relation (4), we obtain formulas for determining tolerances at hypersonic speeds.

This method provides the measurement of the Mach number in the shortest possible time with an error not exceeding a predetermined one, both with uneven and unsteady air flow, and with simpler flows up to a uniform stationary one.

Claims (1)

The method of measuring the Mach number, according to which the signals of the pressure sensors are recorded once in the wind tunnel, determine the Mach number using these signals, and then evaluate the error of the measurement of the Mach number, characterized in that the one-time registration of the signals of the pressure sensors and determining using these signals Mach is repeated many times until the sensor signals fall within the tolerances corresponding to the measured Mach number, and to minimize the pipe operating time, the operations described above asparallelivayut two synchronous in time of the process: In the first single pressure sensor signals recorded in the second determining Mach number is obtained tolerances and control contact pressure sensor signals to these tolerances that are obtained using polynomial dependencies represented by the formulas, or directly by the formulas:
for high subsonic and supersonic speeds

,

,
for hypersonic speeds

,

,
Where:

,

,

,

,

,
Δ [P], Δ [P ₀ ],

are the instrument errors of the sensors of static, complete and complete behind the direct shock pressure compression, respectively, Δ [M] is the specified error in the measurement of the Mach number, ω = Δ [P ₀ ] / Δ [P],

, κ is the adiabatic exponent for air.

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