CN103544053B - Parachute aerodynamic performance analyzing method considering fabric breathability - Google Patents

Abstract

The invention discloses a parachute aerodynamic performance analyzing method considering fabric breathability. A permeation domain is built for the time according to appearance of a parachute, a control equation with a user-identified momentum source item is used to solve the permeation domain, and common flow filed control equations are still used to solve other flow fields. The method has the advantages that influence of fabric breathability on parachute performance analysis is fully considered, the defects that the existing calculation and analyzing methods are large in result error and narrow in application range are overcome, breathability of canopy materials can be simulated accurately and effectively, parachute aerodynamic performance analyzing accuracy is increased, basis is provided for parachute design and optimization, testing times are reduced, and financial and material resources are saved.

Description

A kind of parachute aeroperformance considering fabric breathability analyzes method

Technical field

The present invention relates to a kind of parachute aeroperformance considering fabric breathability and analyze method, belong to aviation lifesaving's technology Field.

Background technology

Breathability is the material properties that fabric is important, and in parachute work process, fabric breathability is pneumatic to parachute Performance impact is the biggest.In most of the cases, parachute aeroperformance analysis does not the most consider fabric breathability, uses based on meter Parachute aeroperformance is analyzed by fluid operator dynamic method by solving N-S equation, but it is (permissible to there is bigger error Reference: McQuilling M, Lobosky L, Sander S.Computational Investigation of Flow Around a Parachute Model.Journal of Aircraft, 2011,48 (1): 34-41. or Noetscher G, Charles R D.Benchmarking Bluff Body Aerodynamics.AIAA2011-2607,2011.).Therefore pin Numerical simulation to fabric breathability, Chinese scholars done preliminary study, and existing ALE method considers fabric air-permeability performance, but Relatively big (Aquelet N, Wang J, Tutt B A, the et al.Euler-Lagrange Coupling with of error Deformable Porous Shells,ASME Pressure Vessels and Piping Division Conference.Vancouver, BC, Canada, 2006,23 27.).Scholar is had the most again to use porous media to simulate fabric Breathability, although computational accuracy is improved, but only simulates one-dimensional direction breathability, is primarily adapted for use in simple flat surface fabric Breathability is simulated, and for the three-dimensional more difficult convergence of parachute flow computation of complex contour, is not used widely and (can join Examine: calculation method for air permeability of canopy fabric, application for a patent for invention number: CN101727541A).At present, in the urgent need to one in engineering Plant and can effectively and accurately consider that the parachute aeroperformance of fabric breathability analyzes method.

Summary of the invention

The technical problem to be solved be for parachute work process exists air-flow through fabric face this One phenomenon, proposes a kind of parachute aeroperformance considering fabric breathability and analyzes method.

The present invention solves above-mentioned technical problem, by the following technical solutions:

A kind of parachute aeroperformance considering fabric breathability analyzes method, and step is as follows:

Step one: simulate this fabric air-permeability performance formula according to fabric air permeability test data, it is thus achieved that permeability is joined Number；

Step 2: by viscosity and the inertia coeffeicent of the sign permeability in breathability formula, is converted into single order resistance Force coefficient and second-order resistance coefficient, self-defined momentum source term, specific as follows:

First, two reduced parameters, single order resistance coefficient C are defined₁With second-order resistance coefficient C₂, its computational methods are as follows

$C_1=a\·\frac{h_f}{h}{,C}_2=b\·\frac{h_f}{h}---\left(1\right)$

Wherein, a, b are permeability parameter, and a is viscosity；B is inertia coeffeicent；h_fFor oozing along fabric face normal direction Territory average thickness thoroughly, h is fabric actual (real) thickness；

Secondly, self-defined additional unit momentum source term:

S_i=-C₁v_i-C₂|v|v_i(2)

Wherein, S_iI to momentum source term；v_iFor i to velocity component；V is velocity, the mould that | v | is velocity, i =1,2,3；

Step 3: set up permeability field grid according to fabric appearance and surround territory, the general flow field grid of permeability field, then entering Row parachute flow computation, uses the N-S governing equation with self-defined momentum source term to solve in permeability field grid, and Territory, flow field grid in addition to fabric uses general N-S governing equation to solve, the wherein flow computation in permeability field grid Solution procedure is specific as follows:

Setting up thickness along fabric normal orientation is h_fPermeability field grid, this permeability field grid is used for describing breathability and knits Thing, wherein momentum governing equation is:

$\frac{\∂\left({\mathrm{\ρv}}_i\right)}{\∂t}+\mathrm{div}\left({\mathrm{\ρv}}_{i}v\right)=\mathrm{div}(\mathrm{\μ}\·{\mathrm{grad}v}_i)-\frac{\∂p}{{\∂x}_i}+S_i---\left(3\right)$

Wherein, ρ is fluid density；T is the time；Div () is that divergence calculates；Grad represents gradient calculation；μ is fluid viscosity Coefficient；P is fluid field pressure；x_iFor i to coordinate；

According to the result calculated, parachute aeroperformance is analyzed.

A kind of parachute aeroperformance considering fabric breathability as the present invention analyzes the method further side of optimization Case, step one is specific as follows:

Record Air permenbility corresponding under different pressure reduction by fabric air permeability test, go out description according to test data fitting and knit The formula of thing breathability:

Δp=(a·v+b·v²) h (4)

Wherein, Δ p represents fabric internal and external flow field pressure reduction；A is viscosity；B is inertia coeffeicent；V is unit unit of time Area Air permenbility, i.e. seepage velocity.

A kind of parachute aeroperformance considering fabric breathability as the present invention analyzes the method further side of optimization Case, in step 3, permeability field grid prism elements divides, and territory, flow field grid uses tetrahedron element to divide.

The present invention uses above technical scheme, compared with prior art has the advantage that

The present invention has taken into full account this important materials attribute of fabric breathability, first when analyzing parachute aeroperformance Fabric face according to complex contour sets up permeability field, and self-defined momentum source term simulation air-flow damages through the momentum produced during fabric Lose, thus breathability can be considered when the fabric flow computation of complex contour, can improve what parachute aeroperformance was analyzed Accuracy, thus result of calculation accuracy is higher, is more suitable for the fabric flow computation of complex contour, provides design for parachute With optimize foundation, and reduce test number (TN), save financial resources and material resources.

Accompanying drawing explanation

Fig. 1 is the method overall flow figure of the present invention.

Fig. 2 is the permeability test schematic diagram data of K59225 type brocade silk.

Fig. 3 is permeability field and territory, flow field schematic diagram.

Fig. 4 is the partial enlarged drawing of Fig. 3.

Fig. 5 is the flow field velocity vectogram after calculating convergence.

Fig. 6 is the flow field velocity vectogram partial enlarged drawing after calculating convergence.

Symbol explanation in figure, 1 is canopy permeability field, and 2 is canopy internal flow field domain, and 3 is canopy External airflow field territory.

Detailed description of the invention

Enforcement to the present invention is further discussed in detail below in conjunction with the accompanying drawings:

With reference first to shown in Fig. 1, a kind of parachute aeroperformance considering fabric breathability of the present invention analyzes method tool Body step is as follows:

Step one: simulate this fabric air-permeability performance formula according to fabric air permeability test data, it is thus achieved that permeability is joined Number；

Step 2: by representing viscosity and the inertia coeffeicent of permeability in breathability formula, be converted into single order resistance Coefficient and second-order resistance coefficient, self-defined momentum source term；

Step 3: set up permeability field grid according to fabric appearance and surround territory, the general flow field grid of permeability field, then entering Row parachute flow computation, uses the N-S governing equation with self-defined momentum source term to solve in permeability field grid, and Territory, flow field grid in addition to fabric uses general N-S governing equation to solve.

In order to feasibility and the accuracy of the present invention are described, using certain model umbrella as objective for implementation, this main canopy of type umbrella Material is K59225 type brocade silk.

The first step: simulate this fabric air-permeability performance formula according to fabric air permeability test data, it is thus achieved that permeability is joined Number；

Use domestic YG461D type digital textile air permeation volume gauge can record Air permenbility (figure corresponding under different pressure reduction 2), according to permeability test data, can simulate and describe fabric air-permeability linearity curve:

Δp=(1.05E6·v+4.9E6·v²)·1E-4

Wherein, Δ p represents fabric internal and external flow field pressure reduction；V is unit unit of time area Air permenbility, i.e. seepage velocity； The viscosity a of K59225 type brocade silk is 1.05E6kg/m³S, inertia coeffeicent b are 4.9E5kg/m⁴, and fabric actual (real) thickness H is 1E-4m.

Second step: the viscosity a and inertia coeffeicent b of permeability will be represented in breathability formula, and be converted into one respectively Rank resistance coefficient and second-order resistance coefficient, self-defined momentum source term.

First, two reduced parameters, single order resistance coefficient C are defined₁With second-order resistance coefficient C₂If, along fabric face normal direction Permeability field average thickness h_fFor 0.03m, it is calculated as follows:

$C_1=a\·\frac{h_f}{h}=1.05E6*\frac{3E-2}{1E-4}=3.15E8$

$C_2=b\·\frac{h_f}{h}=4.9E5*\frac{3E-2}{1E-4}=1.4E8$

Secondly, self-defined adnexa unit momentum source term:

S_i=-C₁v_i-C₂|v|v_i=-3.15e8*v_i-1.47e8*|v|v

Wherein, S_iI to loss of momentum subitem；v_iFor i to velocity component；V is velocity, and | v | is velocity Mould, i=1,2,3；

3rd step: set up permeability field and territory, flow field grid model, and computational analysis.

The permeability field grid and the flow field grid of encirclement permeability field that thickness is 0.03m is set up according to complicated canopy profile. Wherein permeability field prism elements divides, and territory, flow field uses tetrahedron element to divide (Fig. 3 and Fig. 4), realm entry border, flow field Using speed edges (30m/s), outlet border is pressure export (1.01E5Pa), and flow field wall uses sliding wall border.

In parachute flow computation, territory, flow field uses common N-S governing equation to solve, and permeability field uses with certainly Definition momentum source term S_iN-S governing equation solve:

$\frac{\∂\left({\mathrm{\ρv}}_i\right)}{\∂t}+\mathrm{div}\left({\mathrm{\ρv}}_{i}v\right)=\mathrm{div}(\mathrm{\μ}\·{\mathrm{grad}v}_i)-\frac{\∂p}{{\∂x}_i}+S_i$

Wherein, ρ is fluid density；T is the time；Div () is that divergence calculates；Grad represents gradient calculation；μ is fluid viscosity Coefficient；P is fluid field pressure；x_iFor i to coordinate；

Finally carried out this umbrella permanent flow computation (computational methods refer to: Wang Fujun. computational fluid dynamics is divided Analysis CFD software principle and application. Beijing: publishing house of Tsing-Hua University: 1-267), meter is stopped when restraining residual value less than 3E-4 Calculate.

Being analyzed parachute aeroperformance according to the result calculated, during this umbrella stable state, resistance coefficient is 0.776.Should Umbrella has carried out three airdrop tests, and resistance coefficient meansigma methods is 0.712, and error is less than 9%, the analysis result of this explanation present invention The most identical with result of the test, calculate accuracy and be greatly improved.

From calculate convergence after flow field velocity vectogram (Fig. 5 and Fig. 6) it appeared that fluid respectively from canopy edge around Cross canopy, canopy ventilating structure flows to afterbody through canopy, fabric face through canopy, and the fluid velocity through circumferential surface is bright Show less than surrounding air-vent discharge velocity and free speed of incoming flow, show that self-defined momentum source term of the present invention can be effective The breathability situation of simulation fabric.

The present invention is directed to can effectively and accurately consider that the parachute aeroperformance of fabric breathability analyzes this problem, carries Go out a kind of parachute aeroperformance considering fabric breathability and analyzed method, divided by the three-dimensional parachute example of complex contour Analysis it appeared that: result of the present invention is accurate, applied widely completely, overcome that existing method error is big or the lacking of narrow application range Point, fully meets engineering demand.

Claims (3)

1. the parachute aeroperformance considering fabric breathability analyzes method, it is characterised in that step is as follows:

Step one: simulate this fabric air-permeability performance formula according to fabric air permeability test data, it is thus achieved that permeability parameter；

Step 2: will represent viscosity and the inertia coeffeicent of permeability in permeability formula, is converted into single order resistance system Number and second-order resistance coefficient, self-defined momentum source term, specific as follows:

First, two reduced parameters, single order resistance coefficient C are defined₁With second-order resistance coefficient C₂, its computational methods are as follows

$\begin{array}{cc}{C}_1=a\·\frac{h_f}{h}& C_2=b\·\frac{h_f}{h}\end{array}---\left(1\right)$

Wherein, a, b are permeability parameter, and a is viscosity；B is inertia coeffeicent；h_fFor the permeability field along fabric face normal direction Average thickness, h is fabric actual (real) thickness；

Secondly, self-defined additional unit momentum source term:

S_i=-C₁v_i-C₂|v|v_i (2)

Wherein, S_iI to momentum source term；v_iFor i to velocity component；V is velocity, the mould that | v | is velocity, i=1, 2,3；

Step 3: set up permeability field grid according to fabric appearance and surround territory, the general flow field grid of permeability field, then dropping Fall umbrella flow computation, uses the N-S governing equation with self-defined momentum source term to solve in permeability field grid, and except knitting Territory, flow field grid beyond thing uses N-S governing equation to solve, wherein the tool of the flow computation solution procedure in permeability field grid Body is as follows:

Setting up thickness along fabric normal orientation is h_fPermeability field grid, this permeability field grid is used for describing airy fabric, wherein N-S governing equation with self-defined momentum source term is:

$\frac{\∂\left({\mathrm{\ρv}}_i\right)}{\∂t}+div\left({\mathrm{\ρv}}_{i}v\right)=div(\mathrm{\μ}\·{\mathrm{gradv}}_i)-\frac{\∂p}{\∂x_i}+S_i---\left(3\right)$

Wherein, ρ is fluid density；T is the time；Div () is that divergence calculates；Grad represents gradient calculation；μ is fluid viscosity system Number；P is fluid field pressure；x_iFor i to coordinate；

According to the result calculated, parachute aeroperformance is analyzed.

A kind of parachute aeroperformance considering fabric breathability the most according to claim 1 analyzes method, and its feature exists In, step one is specific as follows:

Record Air permenbility corresponding under different pressure reduction by fabric air permeability test, go out to describe fabric according to test data fitting saturating The formula of gas:

Δ p=(a v+b v²)·h (4)

Wherein, Δ p represents fabric internal and external flow field pressure reduction；A is viscosity；B is inertia coeffeicent；V is unit unit of time area Air permenbility, i.e. seepage velocity.

A kind of parachute aeroperformance considering fabric breathability the most according to claim 1 analyzes method, and its feature exists In, in step 3, permeability field grid prism elements divides, and territory, flow field grid uses tetrahedron element to divide.