Model size: length, m diameter, m < 10.5 <0.2 <0.6 <0.2 <0.4 <0.12 <0.5 <0.09 <2.0 <0.

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1 A SYSTE FOR PROVIDING QUALITY OF TESTING, AND ACCURACY OF DETERINING AERODYNAIC CHARACTERISTICS OF ODELS AT TSNIIASH FACILITIES V.A. Kozlovsky, Yu.. Lipnitsky, and V.I. Lapygin TsNIIash, Korolev, oscow region, Russia Together with progress and enhancement of flight vehicles, requirements imposed on a level of onground aerodynamic development and accuracy of experimental determination of aerodynamic characteristics rises. In this connection problems are discussed related to accuracy of determining aerodynamic characteristics through the balance test technique, which is generally used for experimental investigations. Inaccuracy of measurements during experimental investigation of an aerodynamic coefficient is stipulated by the following components: wind tunnel, in particular flow quality and error conditioned by model orientation gear; instrumentation for measuring flow parameters; support devices; quality of the model fabrication, which depends on the model size; in-model strain-gage balance; measuring equipment and measured data acquisition processing system; test technique; measurement assurance. 1. Wind tunnels Aerodynamic complex of TsNIIash consists of six different wind tunnels that provide onground development of rocket-space technology with simulation of flight conditions along a flight vehicle trajectory [1]. It may be separated in two parts: middle-size wind tunnels and large-scale facilities. The complex of middle-size facilities includes U-3 transonic wind tunnel, U-3 transand supersonic wind tunnel with variable density, U-4 supersonic wind tunnel with variable density, and U-6 hypersonic wind tunnel with variable density. The complex of large-scale facilities includes U-1 transonic wind tunnel with variable density and U306-3 super- and hypersonic wind tunnel with variable density. General specifications of the wind tunnel are presented in the following table: Facility U-3 U-3 U-4 U-6 U-1 U306-3 ach number 0.-1.; ; ; 1.8 3; 4; 6; 8 Re Test section dimensions, m odel size: length, m diameter, m <0.5 <0.09 <0.6 <0.09 <0.6 <0. <0.4 <0.1 < 10.5 <0. <.0 <0.5 During operation of the aerodynamic complex, which provides simulation of flight conditions in wide variation ranges of ach number and Reynolds number, some difficulties are stipulated by necessity to ensure identity of measurements for all wind tunnels. In this connection the principal attention was paid to the flow quality in the wind tunnel test section.. The flow quality The wind tunnels are equipped by contoured nozzles with corner point of the structure, TsNIIash []. The design profile provides the high flow uniformity over the test section cut. Non-uniformity of the flow field does not exceed / 0.8.0%. V.A. Kozlovsky, Yu.. Lipnitsky, and V.I. Lapygin, 00 13

2 3. The model orientation gears and support devices TsNIIash wind tunnels are equipped by the precision model orientation gears, which provide displacement of the model along angular coordinates α, β, ϕ and linear coordinates X, Y. Errors of setting and measuring the angular coordinates are σ α,β,ϕ =, and for the linear coordinatesσ X,Y =0.05mm. The gears of the model longitudinal displacement makes possible to position the model in the region of the best flow quality that is very important for investigations at transonic speed due to known peculiarities of the flow in perforated boundaries. Stings should exert minimum influence upon the flow near the model and possess sufficient rigidity in order to reduce frequency and amplitude of the model oscillations. The stings satisfy requirements [3]: a ratio of the sting to model diameter d s /D m =0.4atadistanceabout4 6D m from the model base cut with further increase of d s along a cone with the cone angle easurement of the flow parameters The flow parameters, q are determined basing on two measured pressures P 1 and P ; these quantities may be: static pressure, total pressure, pressure behind normal shock, difference between them. A technique was elaborated in TsNIIash to compare accuracy of means for determining, q respectively to ach number and pressure levels in the wind tunnel forechamber with arbitrary errors of pressure transducers, based on transformation of an expression for relative variance of ach number or dynamic head to the following form D D + D = C, С = f ( ) ξ 1 ' f P1 P P0 ( ) ( ) f ( ) ϕ ' f ( ) ( ) ( 1 ) ξ + ϕ, here f=f( )= Р 1 /Р, ξ i ( ) = Р 0 /Р i, ϕ =D P1 /(D P1 +D P1 ). Recommendations had been given to apply appropriate combinations of pressures for different measurement situations. Of particular interest is a scheme for measuring dynamic pressure at hypersonic velocity of a flow, when q is usually determined through a dependency q =q(р 0, М av ), here the averaged ach number av is based on measurements of a field of ach number values for given nozzle, and total pressure P 0 is measured directly. In this connection calibration of the wind tunnel flow is of great importance, because it is a basis for detecting av at hypersonic velocities and a region of the model position at sub-, trans-, and supersonic flows. 5. The flow calibration The flow calibration includes determination of ach number profiles across the wind tunnel test section, and field of flow angularity, and background noise in the working flow. Investigation of the flow non-uniformity in TsNIIash wind tunnels is conducted through a special precise technique based on differential measurements during flow field scanning by a head or a rack of heads. ach number distribution over the test section is obtained with an error of 0.1%, and then fields of the flow angularity are calculated, the value of av is determined with maximum accuracy and regions for the model location are detected; if necessary, the systematic error due to the flow non-uniformity is taken into account [4, 5]. In order to rise quality of the flow in TsNIIash wind tunnels, special measures were realised directed to reduction of the background noise in the test sections; as a result the noise levels were reduced to values L = db (operation regime with ejector) and L = db (operation regime with turbo- compressor exhauster) [6]. 133

3 6. Aerodynamic models Interest to quality of the models is conditioned by some deviation of the model geometrical similarity caused by manufacturing tolerances. The solution of this problem is based on assumption that each aerodynamic coefficients of force/moment components may be considered as a continuous function of several arguments, which are relative liner L i and angularθ i geometrical dimensions of the model. In this case, if distribution of dimension deviation in limits of manufacturing tolerance is assumed to be random, and an expression for manufacturing tolerance on linear dimensions at D 500 mm is the following: Т =( D D) 1.6 n 6. With known dependency С= С(L 1,... L n, θ 1,..., θ m ) it is possible to define acceptance criteria n for the model fabrication with systematic error less prescribed quantity [7]. In particular, for spherically blunted cone, which axial force coefficient versus geometrical parameters may be represented in the Newton approximation, the acceptance criteria has the following form: 3 Cxp 10 R m 1 C xp n = ln R + 6 ln1.6 sin θk R cos θk ( cos θk) 1 ( ) ( 4.53 R ) m R m sin θk R cos θk cos θ + k where R =R т /R, R т bluntness radius; R midsection radius; ( С хр /С хр ) R relative systematic error of the coefficient С хр due to quality of manufacturing. Required accuracy of manufacturing reduces with increased value of bluntness radius, so for increased model size a level of systematic error due to quality of manufacturing decreases. In accord with these estimations it is recommended to manufacture models with acceptance criteria 6 or Allowable model size As it is shown in Section 6, in order to rise validity of experimental results obtained in wind tunnels it is necessary to increase the model size. On the other hand large scale of the model promotes more complete geometrical similarity between the model and full-scale vehicle because small details of the model are reproduced. Allowable blockage of the flow by the model at transonic velocities is limited due to interference with the wind tunnel walls and it is equal to about 1% of the working section area. For large values of ach number it is elaborated a calculation procedure for determining blockage of super- and hypersonic wind tunnels with Eiffel altitude chamber, and allowable blockage F = F / FcC κ + 1 κ 1 F C = f y z z + p { ( κ ) ( λ1) ( λ1) ( λ) 1 } x K κλ1 κ where F the model midsection area; C x drag coefficient; F C the nozzle exit area; λ 1, λ velocity coefficients at the nozzle exit and at the diffuser inlet; ρ κ pressure loss in oblique shock, which initiates a measurement rhombus at large blockage., 134

4 8. Instrumentation The aerodynamic complex is equipped by Russian and import precise instrumentation. Information measuring systems include the following equipment: multi-channel amplifiers KWS and GC (Germany), accuracy rating %; in-model strain-gage balances (TsNIIash), which have sizes and ranges of measured forces and moments suitable for any types of models; precise strain-gage pressure transducers Statham (USA) with accuracy rating 0.% for measuring flow parameters and base pressure; Tepler shadow devices with viewing field up to 800 mm (Russia) with units for representation of colour images during visualisation of flow patterns. 9. Information acquisition and processing system Acquisition and processing of measurement information is carried out using specific information-computing system (TsNIIash) based on personal computer. The system is equipped by devices for input of signals from balances, pressure and temperature transducers, and model orientation gears through 60 measuring channels with operating speed up to 00 measurements per second for stationary investigations and through 15 measuring channels with operating speed up to 1000 measurements per second for dynamic investigations. 10. easurement assurance of testing easurement assurance at TsNIIash aerodynamic complex is realised through enhancement of units of electrical-physical measurements at wind tunnels specified in Section 8. But in practice implementation of high-quality instrumentation is not always resulted as expected the objective is to determine the models aerodynamic characteristics with required accuracy. Complexity of aerodynamic experiment generates some definite difficulties when it is necessary to provide uniformity of measurements during testing of one model in different wind tunnels. Analysis has shown that uncertainty of results depends significantly on the test technique. In this connection a concept of measurement assurance of aerodynamic researches was elaborated and applied in TsNIIash, which was directed to rise accuracy of aerodynamic characteristics experimental determination and includes the following: metrological certification of the wind tunnel as a main tool in experimental researches, which defines possibility of simulation for one or another examined process; planning of experiment that is development of the model to be examined for provision of similarity of flow in real and onground conditions and choice of particular test technique among fixed list of standard techniques applied at different stages of aerodynamic design; selection among realised measurement techniques or development of a new one, which defines procedure of tests, order of measured information processing and accuracy figure of experimental results. 11. easurement procedure for determination of models aerodynamic characteristics Standard measurement techniques are the basic normative-technical documents, which define technology uniformity at all stages of preparation and operation of measurements for tests at different facilities. 135

5 The techniques include requirements imposed on instrumentation, support devices, conditions of measurement procedure, algorithms of preparation and operation measurement procedures; standards related to accuracy figures, which influence on levels of random and systematic components of errors; they define requirements to managers qualification and procedures for measurement results processing and for evaluation of accuracy figures The techniques are worked up taking into consideration structure scheme of tests, and relative dispersion of measured result for valued of aerodynamic load R may be presented by a following dependency: D D D D D D D D = R S V S S K K S R SB V S S Ky Kf Sr е М y f p In accord with this dependency the dispersion depends on S B characteristics of the balance springy scheme; U stabilisation quality of supply voltage for a bridge; uniformity of S a coefficient of pressure transducer strain-sensitivity and S a coefficient of the bridge sensitivity; stability of amplifying coefficients K y for the amplifier and K f for filter; S r an error of recording device. Random error of measurements may be reduced owing to both reduction of errors of measurement system structure elements and application of more perfect measurement procedures consistent with structure of random error consisting of additive and multiplicative component σ R =ar+b. In case when the multiplicative error ar prevails, positive results are obtained with the help of differential methods, in particular, compensation of a part of aerodynamic loading through a method incompletely balanced bridge permits to decrease relative dispersion of measured force at a level D ( ) R DSB DS D S 1 ( 1 ) D D D U Ky K D Sp = α + α α R SB S S S U Ky K S p where α relative depth of balancing, varying from 0 at unbalanced bridge circuit to 1 at completely balanced bridge. [7]. In case when the additive error b is the main component, increased model scale and dynamic pressure in wind tunnel may increase the accuracy. Really, if measurement errors of dynamic pressure and model size are small, mean square value of a force aerodynamic coefficient may be presented as σ С =b/q S+aC, and for the center of pressure coefficient - σ σ y = + 1, πλ α σ z 4 σ z C p α 3 χ Cy qd where χ = z /Y, λ relative aspect ration of the model. The technique establishes procedure of taking into account and excluding systematic errors, which are mutual influence of the strain-gage balance components [8], temperature influence [7], influence of the model weight and the balance structure [7], influence of the balance and support devices deformation [9]. 1. Testing standard model The level of systematic error that was not excluded and its contribution into the final result is usually estimated through comparison of experimental data obtained for identical models in different wind tunnels at similar regimes. 136

6 At TsNIIash for this purpose proprietary standard models (cone and cylinder-cone configurations) are examined, and also there are examined widely used in practice AGARD-B model at small angle of attack [10-11], and odified Basic Finner (DF) at the large angles [10-11]. Comparison of data for AGARD-B model obtained in TsNIIash with the data adopted as the most probable [1] shows that deviation does not exceed -3%. This value may be considered as critical level of systematic error due to interference with the wind tunnel walls. The level of random error is estimated basing on results of multiple testing. The table presents data on systematic tests with AGARD-B model at ach number М =.0. α, degree С х σс х С y σ Су С Р σ Ср REFERENCES 1. Czajkowski E. Russian Aeronautical Test Facilities. Arlington: Anser Center for International Aerospace Cooperation., Podsypanina N.A,. Shifrin E.G. On a method of contouring for short flat nozzles // Izv. Acad. of Sciences USSR, ekh. Zhidk. i Gaza Podsypanina N.A. Use of hodograph plane for numerical contouring of the Laval Axi-symmetric nozzle // Izv. Acad. of Sciences USSR, ekh. Zhidk. i Gaza c Donald H., Hughes P. A correlation of High Subsonic Afterbody Drag in the Presence of a Propulsive Jet of Support Sting // J. оf Aircraft Vol., 3. Р Andreev V.N., Eremin V.V., Kozlovsky V.A., Lipnitsky Yu.., Filippov S.E. Development of a technique for determining flow fields in supersonic wind tunnels // odern problems of mechanics. oscow University Publ., P Andreev V.N., Filippov S.E., Eremin V.V., Kozlovsky V.A., Lipnitsky Yu.. A technique for determination flow fields in super- and hypersonic tunnels // Intern. Conf. on ethods of Aerophys. Research: Proc. Pt III. Novosibirsk, 000. P Kozlovsky V.A., Lapigin V.I., Lipnitsky Yu.., erkishin A.S., Stekenius K.A. U-1 Transonic wind tunnel for Simulation of a flow over flight vehicles in a wide variation ranges of Reynolds number // 3d Intern. Conf. on Experimental Fluid echanics. Korolev, P Kozlovsky V.A., Stekenius K.A. eans for ensuring accuracy of balances tests with flight vehicle models in wind tunnels // Intern. Conf. Scientific Problems of Cosmonautics and Space Technology. Kaliningrad, TSNIIash, P Dubov B.S. Constraint equation for input and output quantities of multi-component devices // Izmeritelnaya tekhnika Stekenius K.A. A method for determining angular and linear displacements of an aerodynamic model in a flow caused by deformation of its supporting devices // Cosmonautics and Space Technology. Korolev, TSNIIash, Hills R. A Review of easurements on AGARD Calibration odels. AGARDograph 64, November