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A description is presented of a measuring-computing complex for aerodynamic studies based on the
standard VME: its structure and composition and the main characteristics of the channels for measuring
the parameters of the flow, the aerodynamic loads, and the pressure distribution.
Studies of models of aircraft (AC) conducted in wind tunnels (WTs) require that high levels of performance and
cost-effectiveness be attained in the experiment. The functional capabilities, metrological characteristics, and service prop-
erties of the information-measurement systems (IMSs) used in WTs in large part determine the degree of success realized in
solving present-day problems in experimental aerodynamics.
In addition to performing the measurements, it is also necessary to control the special measuring instruments and
auxiliary equipment that is used, perform metrological and diagnostic evaluations of the measurement channels, and analyze
and display the data in real time. By increasing the size of the flows of measurement data and the volume of data that is ana-
lyzed, it becomes possible to perform measuring and computing operations simultaneously and enhance the measuring and
computing capabilities of the system.
It has become an economic necessity to standardize the hardware and software used with wind tunnels and to use
mobile systems and complexes that can service a group of WTs, instead of providing each tunnel with its own costly mea-
suring and computing equipment.
To solve the problems involved in improving the quality and efficiency of aerodynamic testing, the state science cen-
ter at the Central Aerohydrodynamic Institute (TsAGI) has developed open main-modular systems based on the internation-
al standard VME and its extension VXI [1].
The modular organization of VME/VXI systems, their flexibility, and their wide range of uses make it possible to
functionally specialize the subsystems for tests in which computing power is distributed so as to maximize productivity in
collecting and analyzing data. The open architecture, combined with the prospect of improvements in measurement tech-
niques, hardware, and software, will make it possible to systematically plan the reprovisioning of WTs with new measur-
ing-computing systems and complexes.
To re-equip wind tunnels as described above, we have developed measuring-computing complex IVK M2 as part of
the standard VME. The complex makes it possible to measure and analyze data in the main types of model tests (Fig. 1) and
to do so at a qualitatively new level.
With allowance for the features of the primary measurement transducers (sensors) and their service conditions in a
wind tunnel (their location in the AC model, the effect of temperature, moisture, vibrations, long electrical channels, and elec-
trical interference), we developed the following measurement transducers in the standard VME: extensometric balances
(EB), which operate on signals from multi-component force sensors; multi-point pressure modules (MPMs); vibration-fre-
quency transducers (FTs) that measure the parameters of a flow (total p0 and static p pressures); angle transducers (ATs) to
Measurement Techniques, Vol. 43, No. 12, 2000
MEASURING-COMPUTING COMPLEX FOR
AUTOMATING SCIENTIFIC STUDIES IN
WIND TUNNELS
Yu. K. Blokin-Mechtalin UDC 681.121.8
Translated from Izmeritel’naya Tekhnika, No. 12, pp. 31–34, December, 2000. Original article submitted July 12, 2000.
0543-1972/00/4312-1062$25.00 ©2000 Plenum Publishing Corporation1062
1063
Fig. 1. Information-measurement system based on IVK M2 for tests in wind tunnels.
Test parameters Pressure distributionMomentsForces
FT FT RT AT ES MPM MPM
MS
TCBCVB CPB
Casing
VME bus
IBM PC
PC/V
ME
DR
AM
D10
FDC
8
CPU
/VI
AD
C4
AD
C4
AD
C4
AD
C4
CPU
/RD
MX
64
AD
M8
CF
p0 T0p α X Y Z MX MY MZ pi
Uk pk
measure the position of the model α; resistance thermometers (RTs) to determine flow stagnation temperature T0, and other
types of transducers.
The use of programmable electronic components in the transducers, in addition to structural and algorithmic meth-
ods of improving accuracy, has made it possible to develop multi-channel,multi-function measurement modules of the
required precision. That has also helped reduce the dimensions and energy consumption of the measuring instrument.
In the measurement of aerodynamic loads (see Fig. 1) (forces X, Y, Z and moments Mx, My, Mz), the signals from the
components of the extensometric balance EB, the angle transducers ATs measuring the position of the model α, and the resis-
tance thermometers RTs are analyzed simultaneously by a group of secondary transducers with integrating analog-digital con-
verters (ADCs). The modules containing the converters are constructed on the basis of sigma–delta converters or voltage-fre-
quency converters and perform the functions of supplying the resistance strain gages with power, amplifying the signals and
converting them into code, and filtering the dynamic components. A CF clock generator coefficient sets the signal sampling
period for additional post-filtration inside the microcomputer. The range of the input signals of the ADC-4 module, based on
a sigma–delta ADC is ±20 mV – ±2.5 V. The gain is 1–128. The supply voltage of the strain gages ranges from 5 to 10 V
(with a change in polarity). The bit capacity of the ADC is 16–14. The passband is 2.5–270 Hz and is established by means
of a programmable digital filter. The data regeneration rate is 10 Hz – 1 kHz. The percentage main error is 0.02–0.03%.
The weight-measuring subsystem has several advantages [2]:
• the forces,moments,and flow parameters are measured simultaneously, which alleviates the effect of the tran-
sience of the flow on the accuracy with which the aerodynamic loads and the coefficients are determined:
• the subsystem effectively suppresses the dynamic components when the signals from the balance are digitally fil -
tered inside the converter and the microcomputer;
• the subsystem is characterized by a wide dynamic range, high resolution,and high measurement accuracy.
In studying the pressure distribution on models,the signals from the multi-point pressure modules are measured with
the use of analog-digital multiplexer ADM8, which works together with an MX64 analog switch. The needed conversion accu-
racy and speed are achieved by subjecting the MPM signals to preliminary amplification and by using a successive-approxi-
mation ADC which has a capacitance matrix and is automatically calibrated under the control of an internal microcontroller.
The MPM is thermally stabilized by blocks of temperature controllers (TCB). The signals from the temperature sensors of the
MPM are normalized in the TCBs and are measured and monitored by the MX64 and ADM8 modules. The ADM8 module
contains eight single-wire channels for ±10-V signals and four channels for signals in the millivolt range. The bit capacity of
the ADC is 16. Conversion rate is 100 Khz. The module contains a 12-bit register to control the electronic switches inside the
MPM and the module switch (MS). The percentage main error of the ADM8 is within the range ±10 V is 0.01%. Analog
switch MX64 has 64 channels with one-line switching capability and 32 with two-line switching. The switchable signal range
is ±10 V. Connection time is 3 µsec. The percentage main error is 0.01%.
The high accuracy attained in measuring pressure and the stability of the test results can be attributed to the thermal
stabilization of the MPM,the nearly simultaneous recording of pressures,and the averaging of the data. The complex makes it
possible to measure pressure signals at 1024 drainage points on the surface of the model and to study low-frequency processes.
Data-collecting speed is 10,000 points a second. The ranges in which pressure can be measured with the MPM are ±0.2·105 and
±1·105 Pa. The absolute error of the pressure measurements is no greater than 100 Pa, the rms error of the calibrations of the
measurement channels is no greater than 50 Pa,and the percentage main error of pressure measurement is ±0.2% [3].
To a considerable extent, the accuracy with which the parameters of the flow are measured determines the quality
of the results of tests of models. Precision pressure transducers that operate on the basis of frequency of vibration (FTs) are
used to measure total pressure p0 and static pressure p, which are then used to calculate the Mach number and the form drag q.
Signals from FTs are converted into code by multi-channel frequency-measurement module FDC8. The number of channels
in the module is eight,and the capacity of the counters which count the measured and reference frequencies is 232.
Measurement range is 0.5–50 kHz and measurement time (frequency of integration) is 0.01–4 sec. The percentage frequen-
cy-measurement error is ±0.001%. Software can be used to adapt the FDC8 module to the given requirements on measure-
ment accuracy and speed. Programming the number of periods of the measured frequency as a function of its current value
makes it possible to have a prescribed constant (on a scale) error with a constant measurement time [4].
1064
The range of pressures p0 and p that can be measured by transducers of the DVBChU type is 1000–5·105 Pa. The
absolute error of the pressure measurements is 5–10 Pa, and the relative error within the range 2700–5·105 Pa is no greater
than 0.05%. The error made in determining the number M with the DVBChU is 0.001–0.002 units of M. The minimum time
needed to determine the parameters of the flow is 0.02–0.05 sec [5].
The working elements of the complex – the calibrated-voltage blocks CVBs and calibrated-pressure blocks CPBs –
are controlled by a standard discrete input-output module D10. Working standards are used in calibrations of the measure-
ment channels.
Inside single-processor IVK M2,the VME main is connected with an IBM-PC type personal computer (microcom-
puter) through a PC/VME controller. In the multi-processor variant, the PCU/VI processor module may be responsible for
collecting and analyzing data from the balance and the transducers that measure the test parameters,while the CPU/RD col-
lects and analyzes signals from the multi-point pressure modules (MPMs). The DRAM buffer-memory module stores the
measurement data.
The software for the single-processor complex was developed on the basis of the operating systems MS DOS and
Windows NT and includes the following programs: programs to control the measurement modules (device drivers) and the
measurement channels; programs to record and analyze the electric signals from the balance, multi-point pressure modules,
flow-parameter transducers, angle transducers, and temperature sensors; programs for metrological certif ication and cali-
bration of the measurement channels; test programs.
The errors of the measurement channels of the complex are determined from the results of certif ication of the IVK
M2 by the metrological service of TsAGI. On the whole, new-generation measuring-computing complex IVK M2 does the
following:
• it improves accuracy and saves time in measuring the main parameters in aerodynamic testing;
• it ensures a high level of productivity in the experiment by combining different types of measurements and tests
and by allowing measuring and computing operations to be carried out at the same time;
• it provides flexibility in changing the configuration of the complex in accordance with the objective of the exper-
iment;
• it makes it possible to analyze and display measurement data in real time, including during tests;
• it reduces the costs of developing and upgrading the measuring-computing systems of wind tunnels by a factor of
3–4 compared to foreign systems.
REFERENCES
1. Yu. K. Blokin–Mechtalin, Transactions of the Conference-Exhibition Vysokochistye Veshchestva Sopex 93.
VME/VXI Bus in Commercial and Scientific Research. VERA+, Moscow (1993).
2. Yu. K. Blokin-Mechtalin et al.,Izmer. Tekh., No. 5,43 (1998).
3. A. I. Beklemishchev et al.,Izmer. Tekh., No. 8,43 (1994).
4. Yu. K. Blokin-Mechtalin,V. M. Vlasenko, and L. F. Nazarova. Russian Federation Patent No. 2018173. Byul. Izobr.,
No. 15 (1994).
5. Yu. K. Blokin-Mechtalin,V. M. Vlasenko, and L. F. Nazarova,Tr. TsAGI, No. 2567,9 (1995).
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