CN104268399A - Computing method of model parameters in icing wind tunnel experiment under supercooled large droplet condition - Google Patents

Abstract

The invention discloses a computing method of model parameters in an icing wind tunnel experiment under a supercooled large droplet condition and aims at solving the problems that an existing parameter selecting method for a supercooled small droplet icing experiment does not function well if being applied to a supercooled large droplet icing experiment and that the real icing condition cannot be reflected by icing on a scale model of the airplane. The computing method of the model parameters in the icing wind tunnel experiment under the supercooled large droplet condition is capable of orderly giving the experimental parameters of a wind tunnel test section such as air velocity, average droplet grain diameter, air pressure, liquid water content, icing time and low supercooled water temperature corresponding to real icing flying conditions by use of a theoretical derivation and numerical computation method after determining the scale relation of the model and the real airplane. An aircraft icing wind tunnel experiment is performed according to the converted test parameters, and the experimental result and the real result are capable of meeting the similarity requirement on the major characteristics of the icing process. As a result, the computing method of the model parameters in the icing wind tunnel experiment under the supercooled large droplet condition is capable of obtaining the model parameters for the icing wind tunnel experiment; the corresponding parameters are capable of reflecting the real icing condition in the icing wind tunnel experiment.

Description

Cross the computing method of model parameter in icing wind tunnel test under cold large water droplet condition

Technical field

The present invention relates to aerospace field, be specially the computing method of model parameter in icing wind tunnel test under the cold large water droplet condition of a kind of mistake.

Background technology

When aircraft flies at subfreezing temperature, if run into the cloud layer containing super-cooling waterdrop (super-cooling waterdrop refers to that temperature is below the freezing point but still keeps liquid water droplet), droplets impact its in cloud layer on aircraft surfaces, will collision area and near generation icing phenomenon.It is a kind of phenomenon extensively existed in flight practice that aircraft freezes, and is also one of main hidden danger causing flight safety accident.Cross cold large water droplet (English full name Supercooled Large Droplets, usually referred to as SLD) and make a general reference the liquid super-cooling waterdrop that diameter is greater than 50 μm.

Icing wind tunnel as carry out aircraft freeze research major equipment, it is after building up, and test, and must have the choosing method of test parameters, makes test findings and legitimate reading meet similarity.This is owing to carrying out icing wind tunnel test, the restriction of following two aspects can be run into: 1) by the restriction of tunnel size, the size of aircraft components is often too large, and the size of icing wind tunnel test section is relatively little, the demand of carrying out full-scale test can not be met, usually can only test on the model of contracting ratio; 2) restriction of the condition that is put to the test, flying condition and the meteorological pa rameter of icing scope of reality are very wide, as speed, highly, drop diameter, Liquid water content etc., but due to the restriction of manufacturing process and equipment simulating ability, it is impossible for wanting reach these conditions completely in icing wind tunnel simultaneously.Suitably choosing by test parameters, make in the scope that can simulate at icing wind tunnel, choose suitable test condition, finally making freeze (being commonly referred to contracting than freezing) on scale model can reflect the situation of true freeze (being commonly referred to reference to freezing), is the effective way breaking through above restriction.

Existing icing tests parameter choose freezes mainly for crossing cold little water droplet, and SLD freezes, the little water droplet freezing process with routine has larger difference, as SLD freezing process has the kinetic effects such as the distortion of significant water droplet, fragmentation, splashing compared to conventional water droplet, therefore existing icing tests parameter selection method cannot be used for SLD and freeze in the calculating of model parameter.

Through verification experimental verification, for crossing the icing tests parameter selection method of cold little water droplet, to directly apply to the SLD experiment effect that freezes bad, and also do not have to be used for the conversion method of the icing wind tunnel parameter under SLD condition at present.

Summary of the invention

Goal of the invention of the present invention is: the icing tests parameter selection method for the cold little water droplet of existing mistake be used for cold large water droplet freeze experiment effect bad, the problem of true situation of freezing cannot be reflected by freezing on the scale model of aircraft, the computing method of model parameter in icing wind tunnel test under the cold large water droplet condition of a kind of mistake are provided.The present invention is on theoretical modeling and numerical simulation basis, adopt the methods such as the dimensional analysis in similarity theory, focus on the principal character catching aircraft freezing process, establish a kind of test parameters conversion method of icing wind tunnel, be i.e. the computing method of model parameter in the test of a kind of icing wind tunnel.The present invention is after the scale-relation of Confirming model and true aircraft, according to the method for theory deduction and numerical evaluation, corresponding to real icing flight condition, provide the air velocity of test chamber, water droplet mean grain size, atmospheric pressure, Liquid water content, freezing time, these experiment parameters of subcooled water low temperature successively.According to the test parameters obtained that converts, carry out the experiment of aircraft icing wind tunnel, after measured: test findings and legitimate reading can meet the requirement of similarity of the principal character of freezing process.Visible, adopt computing method of the present invention can obtain for the model parameter in icing wind tunnel test, relevant parameter is used for icing wind tunnel experiment can reflect true situation of freezing, and has significant progressive meaning.

To achieve these goals, the present invention adopts following technical scheme:

Cross the computing method of model parameter in icing wind tunnel test under cold large water droplet condition, comprise the steps:

(1) according to by the requirement of analogies, determine by the true profile of analogies and true meteorological condition, described true profile and true meteorological condition comprise following seven parameters: true profile characteristic length L _f, flying speed V _f, super-cooling waterdrop diameter d in air _f, atmospheric pressure P _f, Liquid water content LWC in air _f, freeze T.T. t _f, temperature of incoming flow T _f;

(2) proportionally reduce by the profile of analogies, make one with by the physical model of analogies geometric similarity;

(3) according to physical model prepared by step 2, the aspect of model length L of physical model is determined _m, according to aspect of model length L _mwith true profile characteristic length L _f, the contracting obtaining testing is than number, and contracting than the value of number is

(4) impact factor K is calculated _i, computing formula is as follows:

in this formula, ρ _dfor water-mass density, σ _dfor water surface tension coefficient, μ _dfor water viscosity coefficient, D _dfor drop diameter, V is speed of incoming flow, according to the true meteorological condition that will simulate, calculates K _ivalue;

(5) according to the K that step 4 obtains _ivalue, adopts following formula to obtain judging the value of factor ε:

$\left\{\begin{array}{cc}\mathrm{\&epsiv;}=0.6& K_i>57.7\\ \mathrm{\&epsiv;}=0.5& K_i<=57.7\end{array}\right.;$

(6) according to the V in step one _f, step 4 obtains the value of the ε that step 5 obtains, adopts following formulae discovery to obtain testing the speed V needed _m:

$\frac{V_m}{v_f}={\left(\frac{L_f}{L_m}\right)}^{\frac{1}{\frac{2-\mathrm{\&gamma;}}{\mathrm{\&epsiv;}}-1-\mathrm{\&gamma;}}},$ In this formula, γ=1.4;

(7) according to the V in step one _f, step 4 obtains the value of the ε that step 5 obtains, adopts following formulae discovery to obtain testing the super-cooling waterdrop diameter d needed _m:

$\frac{d_m}{d_f}={\left(\frac{V_f}{V_m}\right)}^{\frac{1}{\mathrm{\&epsiv;}}};$

(8) due under Kelvin scale, the temperature that experiment needs is close with true temperature difference, order initial value be 1;

(9) following formulae discovery is adopted to test the pressure P needed _m:

$\frac{P_m}{P_f}={\left(\frac{V_f}{V_m}\right)}^2\left(\frac{T_m}{T_f}\right);$

(10) adopt following formulae discovery, obtain testing the Liquid water content LWC needed _m:

$\frac{{\mathrm{LWC}}_m}{{\mathrm{LWC}}_f}=\frac{P_m}{P_f}/\left({\left(\frac{L_m}{L_f}\right)}^{0.5}{\left(\frac{V_m}{V_f}\right)}^{0.5}\right);$

(11) adopt following formulae discovery, obtain testing the icing T.T. t needed _m:

$\frac{t_m}{t_f}={\left(\frac{L_m}{L_f}\right)}^{1.5}/\left({\left(\frac{V_m}{V_f}\right)}^{0.5}{\left(\frac{P_m}{P_f}\right)}^{0.5}\right);$

(12) adopt following formulae discovery, obtain testing the temperature of incoming flow T ' needed _m:

$T_m^{\&prime;}=T_f+\frac{{\mathrm{\&theta;}}_m-{\mathrm{\&theta;}}_f}{b}+\frac{V_f^2-V_m^2}{2*C_{p,w}},$

In this formula, C _p,wspecific heat of water, C _p,w=4.184 × 10 ³j/Kg.K ^-1, θ is air energy transformation parameter, and b is the relative temperature factor,

${\mathrm{\&theta;}}_m=(273.15-T_m)-r\frac{{V_m}^2}{2C_p},$

${\mathrm{\&theta;}}_f=(273.15-T_f)-r\frac{{V_f}^2}{2C_p},$

$b=\frac{{\mathrm{LWC}}_f\&CenterDot;V_f\&CenterDot;c_{p,w}}{h_c},$

Wherein, the coefficient of heat convection at stationary point place

K is the pyroconductivity of air; ρ is the density of water; R recovers the factor, r=Pr ^1/2, wherein Pr=0.72;

Cp is the specific heat of air, and μ is aerodynamic force coefficient of viscosity (these two amounts can obtain according to the temperature inquiry of correspondence);

(13) adopt the relative error T of following formulae discovery temperature _δ:

T _δ＝|T′ _m-T _m|/T _m，

If T _δ> 0.000001, then make T _m=T ' _m, turn back to step 9;

If T _δ≤ 0.000001, then T _m=T ' _m, end loop.

In described step 13, work as T _δ≤ 0.000001, then T _m=T ' _m, the L obtained _mbe the aspect of model length that experiment needs, the V obtained _mbe the flying speed that experiment needs, the d obtained _mbe the super-cooling waterdrop diameter that experiment needs, the P obtained _mbe the atmospheric pressure that experiment needs, the LWC obtained _mbe the Liquid water content that experiment needs, the t obtained _mbe the icing T.T. that experiment needs, the T obtained _mbe the temperature of incoming flow that experiment needs.

In order to solve foregoing problems, applicant provides the computing method of model parameter in icing wind tunnel test under the cold large water droplet condition of a kind of mistake.It is as follows that applicant sets up process of the present invention.

1 sets up a kind of icing tests parameter conversion method under SLD condition

The definition of similar parameter, come from icing variant physical process, according to impact freeze principal element, set up accumulated ice test similarity criterion time, following three aspects must be considered: Flow Field, water droplet motion and impact characteristics, accumulated ice process thermodynamic behaviour.

(1) Flow Field is similar

In order to make icing profile on the object plane of geometric similarity also similar, the normalized temperature around material flows also must be similar with pressure distribution.In order to make impingement region have similar Field Characteristics and similar freezing, in icing research, the requirement of stream field is: test model and the necessary geometric similarity of full-scale body; It is 2.0 × 10 that test speed must be greater than Reynolds number ⁵corresponding speed, and be less than the speed corresponding to critical Mach number.

(2) water droplet motion and impact characteristics

Water droplet motion embodies mainly through following aspect with the similar of impact characteristics: the dynamic behavior in water droplet kinematic similitude, motion process is similar, dynamic behavior in knockout process is similar, object plane shock quality is similar.

1. water droplet kinematic similitude

Consider the gravity, buoyancy and the resistance that act on water droplet, according to Newton second law, water droplet trajectory equation can be write as:

$\stackrel{\&RightArrow;}{F}=({\mathrm{\&rho;}}_d-{\mathrm{\&rho;}}_a)v_d\stackrel{\&RightArrow;}{g}+\frac{1}{2}{\mathrm{\&rho;}}_a{A}_d{C}_d|\stackrel{\&RightArrow;}{u}-\stackrel{\&RightArrow;}{u}|(\stackrel{\&RightArrow;}{u}-{\stackrel{\&RightArrow;}{u}}_d),$ In this formula, ρ _aatmospheric density; acceleration of gravity; A _dthe front face area of water droplet, ρ _dwater droplet density; v _dthe volume of water droplet, c _dit is resistance coefficient; represent local gas velocity; represent water drip rate.

Use free stream velocity density (ρ _a) _∞, characteristic length C carries out nondimensionalization, arrangement can obtain:

$\frac{d{\stackrel{\&RightArrow;}{\stackrel{\&OverBar;}{u}}}_d}{\mathrm{d\&tau;}}=\frac{C_d{\mathrm{Re}}_w}{24}\frac{1}{K}(\stackrel{\&RightArrow;}{\stackrel{\&OverBar;}{u}}-\stackrel{\&RightArrow;}{\stackrel{\&OverBar;}{u}}),$ Wherein, K is water droplet inertial parameter, $K=\frac{{\mathrm{\&rho;}}_d{d_{\mathrm{eq}}}^2{V}_{\&infin;}}{18{\mathrm{\&mu;}}_{a}C}.$

Order wherein γ is taken as the value that Reynolds number is relevant a long way off, Ke Yiqu as the similar parameter of water droplet trajectory, it is only water droplet reynolds number Re _δfunction, its value and track have nothing to do.Water droplet movement locus and impact characteristics requirement of similarity can be summarized as:

2. the dynamic behavior in motion process is similar

The governing equation of the damping of drop forced deformation is:

Be analogous to spring forced vibration equation, the peak swing of the damping control of drop forced deformation:

$A=\frac{F_0}{m\sqrt{{({\mathrm{\&Omega;}}^2-{\mathrm{\&omega;}}_0^2)}^2+4{\mathrm{\&beta;}}^2{\mathrm{\&Omega;}}^2}}=\frac{F}{m\sqrt{{(0^2-K/m)}^2+4{\mathrm{\&beta;}}^2{0}^2}}=\frac{F}{K},$

$A=\frac{F}{K}=\frac{C_F{\mathrm{\&rho;}}_g{u}^2}{{\mathrm{\&rho;}}_{l}r}\frac{{\mathrm{\&rho;}}_l{r}^3}{C_k\mathrm{\&sigma;}}=\frac{C_F{\mathrm{\&rho;}}_g{u}^2}{C_k}\frac{r^2}{\mathrm{\&sigma;}},$

A is corresponding water droplet deflection, is water droplet distortion and broken factor of determination, can be write as following form: A=f (ρ _g, u, r, σ).

According to Π theorem, because the number of dimension independently variable is 3, optional its is ρ _g, u, r are dimension, then characteristic can be written as:

$\mathrm{\&Pi;}=\frac{A}{r},{\mathrm{\&Pi;}}_1=\frac{\mathrm{\&sigma;}}{{\mathrm{\&rho;}}_g{u}^{2}r}.$

Then have: Π=Φ (Π ₁).

According to the definition of weber number, $\mathrm{We}=\frac{{\mathrm{\&rho;}}_g{u}^{2}r}{\mathrm{\&sigma;}},{\mathrm{\&Pi;}}_1=\frac{1}{\mathrm{We}},$

As long as weber number is identical, Π ₁just identical, two corresponding amounts just have identical Π, and the namely distortion in motion process of any instant drop is similar with division.

3. the dynamic behavior in knockout process is similar

From spatter model, impact parameter K is depended in the generation of splash phenomena and differentiation:

$K_i={\left(\frac{{{\mathrm{\&rho;}}_d}^3{D_d}^3{V_{n,i}}^5}{{{\mathrm{\&sigma;}}_d}^2{\mathrm{\&mu;}}_d}\right)}^{0.25}.$

Due in water droplet motion process, meet water droplet kinematic similitude, in two similar process, correspondence position has following relation: (V _n,i/ V _∞) _m=(V _n,i/ V _∞) _f.

Define one work as model with exact shape value consistent time, splashing parameter ψ is also equal, then the splashing effects under two states is similar.

4. object plane shock quality is similar

β is the water droplet local collection coefficient of body surface, introduces the concept of clumping factor, is defined as in this formula, ρ _ifor the density of ice, because the similar and test model of water droplet trajectory is the strict contracting ratio of full-scale body, therefore there is β _m=β _f, impact factor then splashing parameter ψ _m=ψ _fif the type of ice is the same, then its density too, as long as therefore clumping factor keeps constant, can meet object plane shock quality similar.

(3) thermodynamic behaviour of freezing process is similar

The icing thermodynamical model set up by Messinger, two states are similar, must have: n _m=n _f, b _m=b _f, wherein: n is freezing proportion, b is the relative temperature factor.

(4) foundation of icing tests parameter choose

According to above-mentioned Flow Field; Water droplet motion and impact characteristics; The similarity analysis of three aspects such as the thermodynamic behaviour of accumulated ice process, the icing similarity criterion comprising SLD condition can be summarized as:

${\left(\stackrel{\&OverBar;}{K}\right)}_m={\left(\stackrel{\&OverBar;}{K}\right)}_f,$

We _m＝We _f，

${\left({\hat{K}}_i\right)}_m={\left({\hat{K}}_i\right)}_f,$

(A _c) _m＝(A _c) _f，

n _m＝n _f，

b _m＝b _f，

Wherein, first, two, two unknown number V and D in three constraint conditions, conflicting between them, three constraints can not meet simultaneously, inertial parameter is most important, this constraint condition is the deciding factor of water droplet motion and knockout process, this condition must meet, second, 3rd constraint condition is conflicting, from numerical value checkout result, the splash effect of water droplet on the impact of freezing than water droplet distortion fragmentation more important, after water droplet stationary point place meets splashing condition, first we ensure the 3rd constraint condition, when water droplet does not produce splashing, get second constraint condition.

Based on above-mentioned research, under applicant obtains SLD condition, the conversion method of icing wind tunnel test, detailed process is as follows.

The first step, as requested, the true profile of given needs simulation and true meteorological condition, true profile and meteorological condition comprise following seven parameters: resemblance length L _f, flying speed V _f, the super-cooling waterdrop diameter d in air _f, atmospheric pressure P _f, the Liquid water content LWC in air _f, freeze T.T. t _f, temperature of incoming flow T _f.Wherein, the prototype of simulation is referred to by analogies.

Second step, according to the principal element that impact is frozen, adopts the icing situation of the given configuration such as icing wind tunnel simulated aircraft, need to ensure the motion of air Flow Field, water droplet and clash into, this three aspect characteristic of thermodynamics of accumulated ice process is similar.Therefore, this profile (namely by the profile of analogies) must be reduced according to a certain percentage, make the physical model that a complete meeting geometric is similar.

3rd step, according to the aspect of model length L of the physical model made _mwith by the true profile characteristic length L of analogies _f, the contracting that can obtain testing is than number, and its value is

4th step, calculates impact factor K _ivalue.

5th step, according to the K that step 4 obtains _ivalue, defines one and judges factor ε:

$\left\{\begin{array}{cc}\mathrm{\&epsiv;}=0.6& K_i>57.7\\ \mathrm{\&epsiv;}=0.5& K_i<=57.7\end{array}\right.$

6th step, calculates the speed V that experiment needs _m.

7th step, calculates the super-cooling waterdrop diameter d that experiment needs _m.

8th step, the asking for of following experiment parameter need the method adopting iteration to calculate, the temperature needed owing to there being experiment under Kelvin scale and true temperature difference not too large, a given initial value, makes the first step cycle calculations is entered from next step.

9th step, d _f, ε value all obtain, by calculate experiment need pressure P _m.

Tenth step, calculates the Liquid water content LWC that experiment needs _m.

11 step, by each parameter value obtained, obtains testing the icing T.T. t needed _m.

12 step, by each parameter value obtained, obtains testing the temperature T ' needed _m.

13 step, the relative error T of accounting temperature _δ, computing formula is as follows: T _δ=| T ' _m-T _m|/T _m.If T _δ> 0.000001, then T _m=T ' _m, turn back to the 9th step, repeat the nine to ten three step.If T _δ≤ 0.000001, then T _m=T ' _m, end loop.Now, the L tried to achieve _m, V _m, d _m, P _m, LWC _m, t _m, T _mseven parameters are Liquid water content in super-cooling waterdrop diameter in aspect of model length that experiment needs, flying speed, air, atmospheric pressure, air, freeze T.T., temperature of incoming flow.

By test, according to convert to these parameters carry out icing wind tunnel test under SLD condition, obtain freeze by with corresponding full-scale condition get off the plane freeze meet requirement of similarity.

The similarity criterion of conventional wind-tunnel, only needing the fundamental equation of fluid motion to carry out nondimensionalization can obtain, and icing tests is similar, except considering hydromechanical requirement, also must consider other influences factor.Four aspects below usual needs meet similarity and require: (1) Flow Field; (2) water droplet motion and impact characteristics; (3) the collection characteristic of water droplet on object plane; (4) icing thermodynamic process.These four aspects intercouple and act on, and often can not meet the demands simultaneously, even there will be conflicting situation, and the similarity criterion more than conventional wind tunnel test is complicated.

Due to the restriction of icing wind tunnel size and test condition, the condition such as size, flying condition, meteorologic parameter and the full-scale condition that are difficult to realize experimental part in icing wind tunnel are completely the same, therefore, the conversion method of test parameters must be set up, suitable test condition is chosen in the scope that icing wind tunnel can be simulated, the result under experimental result and corresponding full-scale condition is made to meet similarity, the icing situation that can reflect in true profile of freezing namely on scale model, just can carry out effective wind tunnel test.

For this reason, applicant is on theoretical modeling and numerical simulation basis, adopt the methods such as the dimensional analysis in similarity theory, focus on the principal character catching aircraft freezing process, establish the computing method of model parameter in icing wind tunnel test under the cold large water droplet condition of a kind of mistake.After the scale-relation of Confirming model of the present invention and true aircraft, according to the method for theory deduction and numerical evaluation, corresponding to real icing flight condition, provide the air velocity of test chamber, water droplet mean grain size, atmospheric pressure, Liquid water content, freezing time, these experiment parameters of subcooled water low temperature successively, the aircraft icing wind tunnel experimental result of carrying out according to the test parameters obtained, the requirement of similarity of the principal character of freezing process can be met with legitimate reading, there is actual application value.

To sum up, in computation process of the present invention, with the addition of the similar of these two dimensionless groups of water droplet weber number and impact factor, make test findings consider the similar process of the factors such as water droplet division, splashing.Meanwhile, to obtain under SLD condition corresponding test parameters in icing wind tunnel test, under SLD condition, carry out icing wind tunnel test according to the present invention, freezing of obtaining to be got off the plane with corresponding full-scale condition and is icingly met similarity requirement.

Accompanying drawing explanation

Examples of the present invention will be described by way of reference to the accompanying drawings, wherein:

Fig. 1 is the normalization drop collection index contrast figure of embodiment 1.

Fig. 2 is that the normalization of embodiment 1 is frozen profile comparison diagram.

Fig. 3 is the normalization drop collection index contrast figure of embodiment 2.

Fig. 4 is that the normalization of embodiment 2 is frozen profile comparison diagram.

Fig. 5 is normalization drop collection index contrast figure.

Fig. 6 is that normalization is frozen profile comparison diagram.

Fig. 7 is normalization drop collection index contrast figure.

Fig. 8 is that normalization is frozen profile comparison diagram.

Embodiment

All features disclosed in this instructions, or the step in disclosed all methods or process, except mutually exclusive feature and/or step, all can combine by any way.

Arbitrary feature disclosed in this instructions, unless specifically stated otherwise, all can be replaced by other equivalences or the alternative features with similar object.That is, unless specifically stated otherwise, each feature is an example in a series of equivalence or similar characteristics.

Embodiment 1

Choose the full-scale as a reference profile of NACA0012 aerofoil profile that chord length is 0.5m, test model size is taken as 0.3m.

Live Flying condition is: chord length: L _f=0.5m; Flying speed: V _f=95.0m/s; Pressure: P _f=91032Pa; Drop diameter: d _f=60 μm; Liquid water content: LWC _f=0.22g/m ³; Freezing time: t _f=6min; Freezing temperature: T _f=253K.

Adopt technical scheme of the present invention, calculate, the test parameters that can calculate model is: chord length: L _m=0.3m; Flying speed: V _m=119.1m/s; Drop diameter: d _m=38 μm; Liquid water content: LWC _m=0.163g/m ³; Freezing time: t _f=232.9s; Freezing temperature: T _f=255.2K.

For the Live Flying condition of embodiment 1 and the test condition of its correspondence, in Fig. 1,2, sets forth normalized Comparative result figure.Fig. 1 to be normalization drop collection index contrast figure, Fig. 2 be normalization freezes profile comparison diagram.In Fig. 1,2, lines represent full-scale condition, and initial point represents experiment condition.

Embodiment 2

Choose the full-scale as a reference profile of NACA0012 aerofoil profile that chord length is 0.5m, test model size is taken as 0.3m.

Live Flying condition is:; Chord length: L _f=0.5m; Flying speed: V _f=90.0m/s; Pressure: P _f=89032Pa; Drop diameter: d _f=80 μm; Liquid water content: LWC _f=0.15g/m ³; Freezing time: t _f=6min; Freezing temperature: T _f=248K.

Corresponding with Live Flying condition, the test parameters calculating model is: chord length: L _m=0.3m; Flying speed: V _m=113.6m/s; Drop diameter: d _m=50.2 μm; Liquid water content: LWC _m=0.109g/m ³; Freezing time: t _f=234.2s; Freezing temperature: T _f=251.2K.

For the Live Flying condition of embodiment 2 and the test condition of its correspondence, in Fig. 3,4, sets forth normalized Comparative result figure.Fig. 3 to be normalization drop collection index contrast figure, Fig. 4 be normalization freezes profile comparison diagram.In Fig. 3,4, lines represent full-scale condition, and initial point represents experiment condition.

Embodiment 3

Choose the full-scale as a reference profile of NACA0012 aerofoil profile that chord length is 0.5m, test model size is taken as 0.3m.

Live Flying condition: chord length: L _f=0.5m; Flying speed: V _f=89.0m/s; Pressure: P _f=89032Pa; Drop diameter: d _f=100 μm; Liquid water content: LWC _f=0.5g/m ³; Freezing time: t _f=6min; Freezing temperature: T _f=252K.

The test parameters calculating model is: chord length: L _m=0.3m; Flying speed: V _m=123.4m/s; Drop diameter: d _m=58 μm; Liquid water content: LWC _m=0.286g/m ³; Freezing time: t _f=271s; Freezing temperature: T _f=253K.

For the Live Flying condition of embodiment 3 and the test condition of its correspondence, in Fig. 5,6, sets forth normalized Comparative result figure.Fig. 5 to be normalization drop collection index contrast figure, Fig. 6 be normalization freezes profile comparison diagram.In Fig. 5,6, lines represent full-scale condition, and initial point represents experiment condition.

Embodiment 4

Choose the full-scale as a reference profile of NACA0012 aerofoil profile that chord length is 0.6m, test model size is taken as 0.3m.

Live Flying condition: chord length: L _f=0.6m; Flying speed: V _f=100.0m/s; Pressure: P _f=89032Pa; Drop diameter: d _f=120 μm; Liquid water content: LWC _f=0.145g/m ³; Freezing time: t _f=6min; Freezing temperature: T _f=243K.

Adopt technical scheme of the present invention, calculate, the test parameters that can calculate model is: chord length: L _m=0.3m; Flying speed: V _m=159.3m/s; Drop diameter: d _m=55 μm; Liquid water content: LWC _m=0.065g/m ³; Freezing time: t _f=251.7s; Freezing temperature: T _f=247K.

For the Live Flying condition of embodiment 4 and the test condition of its correspondence, in Fig. 7,8, sets forth normalized Comparative result figure.Fig. 7 to be normalization drop collection index contrast figure, Fig. 8 be normalization freezes profile comparison diagram.In Fig. 7,8, lines represent full-scale condition, and initial point represents experiment condition.

Can find out from above result of calculation, coincide better after the local collection coefficient normalization on full-scale body and model, show water droplet trajectory similar parameter of the present invention and meet requirement of similarity according to the drop diameter parameter relationship formula that this parameter is set up; On full-scale and model, the profile of ice is almost completely the same, illustrates that icing similarity criterion that the present invention adopts is to ice type contracting ratio well; Can find out from normalized water droplet trajectory figure, it is fine that the water droplet trajectory water droplet trajectory that on full-scale body and model, same position is launched before splashing meets, and illustrates that the similarity criterion that the present invention develops can have good similarity to the amount of the water droplet deformation position in SLD freezing process, splash judgement and water-drop sputtering.

The present invention is not limited to aforesaid embodiment.The present invention expands to any new feature of disclosing in this manual or any combination newly, and the step of the arbitrary new method disclosed or process or any combination newly.

Claims (2)

1. cross the computing method of model parameter in icing wind tunnel test under cold large water droplet condition, comprise the steps:

(1) according to by the requirement of analogies, determine by the true profile of analogies and true meteorological condition, described true profile and true meteorological condition comprise following seven parameters: true profile characteristic length L _f, flying speed V _f, super-cooling waterdrop diameter d in air _f, atmospheric pressure P _f, Liquid water content LWC in air _f, freeze T.T. t _f, temperature of incoming flow T _f;

(2) proportionally reduce by the profile of analogies, make one with by the physical model of analogies geometric similarity;

(3) according to physical model prepared by step 2, the aspect of model length L of physical model is determined _m, according to aspect of model length L _mwith true profile characteristic length L _f, the contracting obtaining testing is than number, and contracting than the value of number is

(4) impact factor K is calculated _i, computing formula is as follows:

in this formula, ρ _dfor water-mass density, σ _dfor water surface tension coefficient, μ _dfor water viscosity coefficient, D _dfor drop diameter, V is speed of incoming flow, according to true meteorological condition, calculates K _ivalue;

(5) according to the K that step 4 obtains _ivalue, adopts following formula to obtain judging the value of factor ε:

$\left\{\begin{array}{cc}\mathrm{\&epsiv;}=0.6& K_i>57.7\\ \mathrm{\&epsiv;}=0.5& K_i<=57.7\end{array}\right.;$

(6) according to the V in step one _f, step 4 obtains the value of the ε that step 5 obtains, adopts following formulae discovery to obtain testing the speed V needed _m:

$\frac{V_m}{v_f}={\left(\frac{L_f}{L_m}\right)}^{\frac{1}{\frac{2-\mathrm{\&gamma;}}{\mathrm{\&epsiv;}}-1-\mathrm{\&gamma;}}},$ In this formula, γ=1.4;

(7) according to the V in step one _f, step 4 obtains the value of the ε that step 5 obtains, adopts following formulae discovery to obtain testing the super-cooling waterdrop diameter d needed _m:

$\frac{d_m}{d_f}={\left(\frac{V_f}{V_m}\right)}^{\frac{1}{\mathrm{\&epsiv;}}};$

(8) due under Kelvin scale, the temperature that experiment needs is close with true temperature difference, order initial value be 1;

(9) following formulae discovery is adopted to test the pressure P needed _m:

$\frac{P_m}{P_f}={\left(\frac{V_f}{V_m}\right)}^2\left(\frac{T_m}{T_f}\right);$

(10) adopt following formulae discovery, obtain testing the Liquid water content LWC needed _m:

$\frac{{\mathrm{LWC}}_m}{{\mathrm{LWC}}_f}=\frac{P_m}{P_f}/\left({\left(\frac{L_m}{L_f}\right)}^{0.5}{\left(\frac{V_m}{V_f}\right)}^{0.5}\right);$

(11) adopt following formulae discovery, obtain testing the icing T.T. t needed _m:

$\frac{t_m}{t_f}={\left(\frac{L_m}{L_f}\right)}^{1.5}/\left({\left(\frac{V_m}{V_f}\right)}^{0.5}{\left(\frac{P_m}{P_f}\right)}^{0.5}\right);$

(12) adopt following formulae discovery, obtain testing the temperature of incoming flow needed

$T_m^{\&prime;}=T_f+\frac{{\mathrm{\&theta;}}_m-{\mathrm{\&theta;}}_f}{b}+\frac{V_f^2-V_m^2}{2*C_{p,w}},$

In this formula, C _{p, w}specific heat of water, C _p,w=4.184 × 10 ³j/Kg.K ^-1, θ is air energy transformation parameter, and b is the relative temperature factor,

${\mathrm{\&theta;}}_m=(273.15-T_m)-r\frac{{V_m}^2}{2C_p},$

${\mathrm{\&theta;}}_f=(273.15-T_f)-r\frac{{V_f}^2}{2C_p},$

$b=\frac{{\mathrm{LWC}}_f\&CenterDot;V_f\&CenterDot;c_{p,w}}{h_c},$

Wherein, the coefficient of heat convection at stationary point place

K is the pyroconductivity of air; ρ is the density of water; R recovers the factor, r=Pr ^1/2, wherein Pr=0.72,

Cp is the specific heat of air, and μ is aerodynamic force coefficient of viscosity;

(13) adopt the relative error T of following formulae discovery temperature _δ:

$T_{\mathrm{\&delta;}}=|T_m^{\&prime;}-T_m|/T_m,$

If T _δ> 0.000001, then make T _m=T ' _m, turn back to step 9;

If T _δ≤ 0.000001, then T _m=T ' _m, end loop.

2. according to claim 1 or 2, cross the computing method of model parameter in icing wind tunnel test under cold large water droplet condition, it is characterized in that, in described step 13, work as T _δ≤ 0.000001, then T _m=T ' _m, the L obtained _mbe the aspect of model length that experiment needs, the V obtained _mbe the flying speed that experiment needs, the d obtained _mbe the super-cooling waterdrop diameter that experiment needs, the P obtained _mbe the atmospheric pressure that experiment needs, the LWC obtained _mbe the Liquid water content that experiment needs, the t obtained _mbe the icing T.T. that experiment needs, the T obtained _mbe the temperature of incoming flow that experiment needs.