CN102663238A - Ice surface roughness measuring method based on liquid water distribution - Google Patents

Abstract

The invention discloses an ice surface roughness measuring method based on liquid water distribution, which belongs to the field of ice surface roughness evaluation. According to the method, for the different liquid water distributions of an ice surface, a roughness model of a subarea is established, namely the height ofa water layer ofthe ice surface is compared with the height of a broken critical water layer. When the former is larger, the roughness equals to the wave height ofthe water layer surface; and when the latter is larger, the roughness equals to the height of the stream formed by the breaking of the water layer. The method updates the roughness value based on the features of liquid water of the actual ice surface at each time step, so that the roughness evaluation is closer toan actual icing process.

Description

Icing surfaceness balancing method based on liquid water distribution

Technical field

The present invention relates to the icing numerical computation method of a kind of aircraft, relate in particular to a kind of icing surfaceness balancing method, belong to ice sheet surfaceness evaluation areas based on liquid water distribution.

Background technology

When aircraft passed through the cloud layer that contains super-cooling waterdrop, the leading edge of a wing can freeze usually, caused the flying quality of aircraft to descend.In order to guarantee the flight safety of aircraft, and reduce the test resource consumption, improve research efficient, must greatly develop the aircraft numerical simulation technology that freezes.

And in the numerical evaluation of freezing; Need simulation ice sheet propagation process in time; Therefore weigh problem with regard to the degree of roughness that relates to ice sheet surface on each time step; Be all must upgrade roughness after each time step, rationally weigh the influence of accumulated ice stream pressure coefficient and water droplet collection coefficient according to current time surface area ice condition condition, and to the influence of the heat and mass generation of ice sheet, subcooled water and air three-phase.Conventional at present icing surfaceness balancing method is equivalent grains of sand roughness height model; The grains of sand of promptly arranging the degree of roughness equivalence on ice sheet surface for equal diameter; Calculate the constant roughness value; In computation process, postpone outside the surperficial ice sheet, no longer carry out roughness and upgrade, adopt the roughness value of this constant in the whole icing calculating as ice sheet.This method is expressed icing roughness and is the function of room and time, the difference of roughness on continuous formation of the ice sheet that is beyond expression out and the model diverse location, and the therefore icing error of calculating is bigger.

Summary of the invention

The present invention is directed to the defective of prior art, and propose a kind of icing surfaceness balancing method, to realize the real-time update of ice sheet surfaceness in the freezing process based on liquid water distribution.

Theing contents are as follows of this method:

The principle of mass conservation according to control volume obtains the surperficial moisture film height h that freezes _w,, confirm that disrumpent feelings critical moisture film height h takes place moisture film according to the stress balance model _F-r:

$h_{f-r}={\left[\frac{6\·{{\mathrm{\μ}}_w}^2\·\mathrm{\σ}\·(1-\cos \mathrm{\θ})}{{\mathrm{\ρ}}_w{{\mathrm{\τ}}_a}^2}\right]}^{\frac{1}{3}}$

Work as h _w＞h _F-rThe time, moisture film is continuous, roughness k _sEqual the water film surface wave height, that is:

Work as h _w≤h _F-rThe time, moisture film is disrumpent feelings formation streams, roughness k _sEqual local streams height, that is: k _s=R (1-cos θ);

In the above formula: μ _wBe hydrodynamic force viscosity, σ is a water film surface tension force, and θ is the contact angle of water on the ice face, ρ _wBe water-mass density, τ _aBe the air-flow shear stress that moisture film receives, g is an acceleration of gravity, and R is the streams radius.

Technique effect:

This method can be upgraded the roughness on ice sheet surface on each time step; Solved the measurement problem of ice sheet surface roughness in the icing calculating well; Make the assessment of ice sheet surfaceness more near actual freezing process, lay a good foundation with the simulation precision of ice shape for improving follow-up icing heat and mass.

Description of drawings

Fig. 1 is the surface water membrane flow synoptic diagram that freezes, and alphabetical implication: g representes acceleration of gravity among the figure, g _sExpression acceleration of gravity is along the component of surperficial tangential direction, g _yExpression acceleration of gravity is along the component of surface normal direction, p _aThe expression air-flow acts on the pressure of water film surface, τ _a(s) the expression air-flow acts on the shear stress of water film surface, u (s, y) velocity distribution in the expression moisture film, h _iThe expression ice layer thickness, h _wThe expression water film thickness.

Fig. 2 is the disrumpent feelings process synoptic diagram of moisture film, and dz representes that exhibition is to infinitesimal length among the figure.

Fig. 3 is the disrumpent feelings position of a moisture film force analysis synoptic diagram, and alphabetical implication: θ is the contact angle of water on the ice face among the figure, F _pThe pressure of the disrumpent feelings position of moisture film that changes into for upper reaches kinetic energy, F _{σ 1}, F _{σ 2}Be suffered surface tension on the arc wheel profile of the disrumpent feelings position of moisture film.

Fig. 4 is a streams model synoptic diagram, and alphabetical implication: θ is the contact angle of water on the ice face among the figure, and R is the streams radius, and χ is the streams spacing.

Fig. 5 is the analog computation comparison diagram as a result that freezes.

Embodiment

Be described further in the face of the present invention down.

Icing surfaceness is the generation that freezing process is induced by the surface, according to experimental phenomena, has one deck thin water film on the icing surface of icing meteorological condition lower wing, and is as shown in Figure 1.Because moisture film constantly with between air-flow and the ice sheet caloic takes place exchanges in the process of flow further downstream, it highly can constantly reduce, when it highly reaches critical altitude, and moisture film is disrumpent feelings formation streams, as shown in Figure 2.Therefore, this method is set up the roughness model of subregion to the different liquid water distribution state in surface that freezes, and particular content is following:

Obtain the moisture film height h of the icing surperficial any place of wing according to the principle of mass conservation of control volume _w,, confirm that disrumpent feelings critical moisture film height h takes place moisture film according to the stress balance model _F-r, the force analysis of the disrumpent feelings position of moisture film is as shown in Figure 3.

$h_{f-r}={\left[\frac{6\·{{\mathrm{\μ}}_w}^2\·\mathrm{\σ}\·(1-\cos \mathrm{\θ})}{{\mathrm{\ρ}}_w{{\mathrm{\τ}}_a}^2}\right]}^{\frac{1}{3}}$

With moisture film height h _wWith critical moisture film height h _F-rCompare:

1. work as h _w＞h _F-rThe time, moisture film is continuous, roughness k _sEqual the water film surface wave height, that is:

2. work as h _w≤h _F-rThe time, moisture film is disrumpent feelings formation streams, roughness k _sEqual local streams height, that is: k _s=R (1-cos θ).

In the above formula: μ _wBe hydrodynamic force viscosity, σ is a water film surface tension force, and θ is the contact angle of water on the ice face, ρ _wBe water-mass density, τ _aBe the air-flow shear stress that moisture film receives, g is an acceleration of gravity, and R is the streams radius.

Suppose streams, the disrumpent feelings back of moisture film along opening up to being uniformly distributed with, the xsect molded lines in streams is circular arc, and is as shown in Figure 4.

On very first time step-length, the roughness value that embeds in the calculating of freezing is pressed grains of sand roughness Model Calculation, that is:

$k_s=0.6839{\left[\frac{k_s/c}{{(k_s/c)}_{\mathrm{base}}}\right]}_{\mathrm{LWC}}\·{\left[\frac{k_s/c}{{(k_s/c)}_{\mathrm{base}}}\right]}_{T_s}\·{\left[\frac{k_s/c}{{(k_s/c)}_{\mathrm{base}}}\right]}_{\mathrm{MVD}}\·{\left(\frac{k_s}{c}\right)}_{\mathrm{base}}\·c$

In the formula: k _sBe roughness value, promptly often be worth roughness; C is the chord length of wing; LWC representes cloud layer aqueous water content, the g/m of unit ³, it is the set-point according to environmental change; T _sEnvironment temperature, unit K; MVD representes water droplet average volume diameter, the μ m of unit, and it is the set-point according to environmental change;

On each time step after very first time step-length, all upgrade roughness value, and upgrade freeze the calculating required local Reynolds number and the coefficient of heat transfer by new roughness value based on actual ice sheet surface liquid water distribution state.

In order to verify the feasibility of this method, we adopt this method to calculate the NACA0012 airfoil surface to freeze, and with contrast with icing tunnel test findings under the operating mode and LEWICE software simulation result, as shown in Figure 5, it is good to coincide.

Claims (1)

1. icing surfaceness balancing method based on liquid water distribution is characterized in that:

Theing contents are as follows of this method:

The principle of mass conservation according to control volume obtains the surperficial moisture film height h that freezes _w,, confirm that disrumpent feelings critical moisture film height h takes place moisture film according to the stress balance model _F-r:

$h_{f-r}={\left[\frac{6\·{{\mathrm{\μ}}_w}^2\·\mathrm{\σ}\·(1-\cos \mathrm{\θ})}{{\mathrm{\ρ}}_w{{\mathrm{\τ}}_a}^2}\right]}^{\frac{1}{3}}$

Work as h _w＞h _F-rThe time, moisture film is continuous, roughness k _sEqual the water film surface wave height, that is:

Work as h _w≤h _F-rThe time, moisture film is disrumpent feelings formation streams, roughness k _sEqual local streams height, that is: k _s=R (1-cos θ);

In the above formula: μ _wBe hydrodynamic force viscosity, σ is a water film surface tension force, and θ is the contact angle of water on the ice face, ρ _wBe water-mass density, τ _aBe the air-flow shear stress that moisture film receives, g is an acceleration of gravity, and R is the streams radius.

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