CN104699951A - Generation method of turbulent flow entry data - Google Patents

Abstract

The invention discloses a generation method of turbulent flow entry data. The generation method specifically comprises the following steps: step one, obtaining average parameters of an entry cross-section position; step two, extracting pulsation information from a downstream recovery section, decomposing spatial intrinsic features of the pulsation information, performing proportion transformation according to a similarity law, and then taking results as pulsation parameters of an entry; step three, adding the average parameters and the pulsation parameters to form instantaneous parameters of the turbulent flow entry. With adoption of the generation method, the obtained boundary conditions of turbulent flow are fully close to the actual turbulent flow data, and can effectively guarantee the authenticity and validity of the main simulation.

Description

A kind of turbulent flow entry data generation method

Technical field

The present invention relates to hydrodynamics technology field, the invention discloses a kind of turbulent flow entry data generation method.

Background technology

Boundary layer is the simplest a kind of in all flow phenomenons, even so simple model, when its downstream, can go through the laminar flow stage, and being then that laminar flow twists the stage to turning of turbulent transition, is finally full-blown stage of turbulent flow.The flow phenomenon of the complexity experienced in this process, people can't understand so far completely.Turbulent boundary layer relates to the many aspects of industrial circle simultaneously, as turbulent flow drag reduction, turbulence noise, turbulent flow vibration etc., and these all need from the simplest boundary-layer flow research, progressively tend to practical application, so boundary layer becomes the basis of turbulent flow research.

For the turbulent boundary layer of spatial development, it is very responsive to upstream conditions, so when adopting method for numerical simulation (large eddy simulation LES or direct Numerical DNS) to simulate turbulent boundary layer, its inlet boundary condition is very important, be directly connected to numerical evaluation success or not, the boundary condition schematic diagram of LES or DNS simulation as shown in Figure 1, turbulent flow entry condition is directly connected to the success or not of LES or DNS simulation.Because the flowing information of turbulent flow porch (especially pulsation information) is unknown and time dependent, usually need people for providing when simulating, people is whether the pulsation information provided meets turbulence characteristics, does is it close to true turbulent flow that turbulent flow is fully developed in the downstream obtained thus? this becomes the problem that researchist extremely pays close attention to.

For the research of turbulent flow entry condition, the most basic way is by instantaneous flow parameter be decomposed into mean parameter and fluctuating parameter two, mean parameter is on average obtained by time or space integral, and fluctuating parameter is then the residual quantity of instantaneous parameters and mean parameter, that is: here any one flow parameter in representation speed, temperature.

Lot of domestic and international scholar has carried out the research work of this respect for this respect nearly ten years, roughly comprises: 1. data or DNS calculate data configuration turbulent flow entry data by experiment.These class methods need prior given experimental data or DNS calculates data, so just limit the use of the method; 2. adopt laminar flow profile as the mean parameter of porch, and fluctuating parameter is taken as random quantity, both superpose rear synthesis turbulent flow entry data.These class methods need the whole process of simulation from laminar flow to turbulent flow, need to grow very much distance and could obtain turbulent flow data, bring very large calculated amount, the efficiency of the serious method that have impact in downstream.3., by flowing to relaxed periodicity boundary condition, structure aided solving obtains turbulent flow entry data.These class methods are the laws of similitude based on turbulent boundary layer, are carried out by the flowing information in downstream introducing the entry condition of upstream as upstream after data processing, thus become a kind of approximate period condition.The drift of average cross-section can be caused after this class methods long-time integration, cause the boundary layer thickness of porch to meet specified criteria.

Summary of the invention

For above-mentioned problem, the present invention proposes a kind of turbulent flow entry data generation method.

Object of the present invention is realized by following technical proposals:

A kind of turbulent flow entry data generation method, it specifically comprises the following steps: step one, obtains the mean parameter at entrance section place; Step 2, from downstream recovery cross section, extract pulsation information, after first this pulsation information being carried out the intrinsic characteristics resolution process in space, then carry out transformation of scale according to the law of similitude, then using the fluctuating parameter of result as entrance; Step 3, mean parameter and fluctuating parameter are added synthesis turbulent flow entrance instantaneous parameters.

Further, said method also comprises and constructs an aided solving to generate turbulent flow entry data.

Further, the mean parameter at the entrance section place in above-mentioned steps one obtained by the Reynolds average equation solving Navier-Stokes equation.

Further, above-mentioned steps two also comprises the weight function design of boundary layer reconstruct.

Further, the weight function design of above-mentioned boundary layer reconstruct specifically comprises the following steps:

Step S21. extracts flowing instantaneous parameters from recovery section it is averaged and obtains mean parameter and mean parameter is decomposed into interior layer parameter in boundary layer with outer layer parameter

Layer parameter in step S22. obtains according to step S21 with outer layer parameter and the law of similitude in boundary layer, calculate the interior layer parameter at entrance section place with outer layer parameter

Step S23. reconstructs mean parameter wherein W is weight function;

Step S24. optimizes weight function W, makes the parameter reconstructed with given parameter reaching unanimity, namely by optimizing weight function W, making minimum.

Further, the fluctuating parameter of entrance in above-mentioned steps two computing method be specially: first extract flowing fluctuating parameter from recovery section then POD resolution process is carried out to this pulsation information, ignore the high order mode of little energy, obtain new fluctuating parameter then by this fluctuating parameter resolve into interior layer parameter with outer layer parameter and the internal layer fluctuating parameter of porch is calculated by the law of similitude with outer fluctuating parameter fluctuating parameter is reconstructed again by with optimizing the weight function W obtained using the new pulsation information that the obtains fluctuating parameter as aided solving porch

By adopting above technical scheme, the present invention has following beneficial effect: one aspect of the present invention obtains the mean parameter at entrance section place, in addition on the one hand by being carried out by the flowing information in downstream introducing the fluctuating parameter of upstream as upstream entrance after data processing, and mean parameter and fluctuating parameter are added synthesis turbulent flow entrance instantaneous parameters.Two kinds of methods in such methods combining prior art.The data close to true turbulent flow of the turbulent boundary sufficient condition obtained like this, effectively can ensure authenticity and the validity of main simulation.

Accompanying drawing explanation

Fig. 1 is the boundary condition schematic diagram of LES or DNS simulation.

Fig. 2 is the relation schematic diagram between aided solving and main simulation.

Fig. 3 is the aided solving schematic diagram generating turbulent flow entry data.

Fig. 4 is the computational fields of aided solving.

Fig. 5 is aiding data procedure chart.

Embodiment

Below in conjunction with Figure of description, describe the specific embodiment of the present invention in detail.

The invention discloses a kind of turbulent flow entry data generation method, it specifically comprises the following steps: step one, obtains the mean parameter at entrance section place; Step 2, from downstream recovery cross section, extract pulsation information, after first this pulsation information being carried out the intrinsic characteristics resolution process in space, then carry out transformation of scale according to the law of similitude, then using the fluctuating parameter of result as entrance; Step 3, mean parameter and fluctuating parameter are added synthesis turbulent flow entrance instantaneous parameters.One aspect of the present invention obtains the mean parameter at entrance section place, in addition on the one hand by being carried out by the flowing information in downstream introducing the fluctuating parameter of upstream as upstream entrance after data processing, and mean parameter and fluctuating parameter are added synthesis turbulent flow entrance instantaneous parameters.The middle method 2 of such methods combining prior art and method 3.The data close to true turbulent flow of the turbulent boundary sufficient condition obtained like this, effectively can ensure authenticity and the validity of main simulation.

In the present embodiment, construct an aided solving to complete above-mentioned step, this aided solving is specifically designed to and generates turbulent flow entry data, the relation schematic diagram between aided solving as shown in Figure 2 and main simulation.The outlet data of aided solving is as the turbulent flow entry condition of the main simulation of LES or DNS.

Further, the mean parameter at the entrance section place in above-mentioned steps one obtained by the Reynolds average equation solving Navier-Stokes equation.Method 2 adopts laminar flow profile as average stream, and superposition random pulse field, needs to simulate whole laminar flow to turbulent flow evolution, and calculated amount is very large, and the application adopts the Reynolds average equation solving Navier-Stokes equation to obtain, and reduces calculated amount.

Further, above-mentioned steps two also comprises the weight function design of boundary layer reconstruct, and it specifically comprises the following steps:

Step S21. extracts flowing instantaneous parameters from recovery section it is averaged and obtains mean parameter and mean parameter is decomposed into interior layer parameter in boundary layer with outer layer parameter

Layer parameter in step S22. obtains according to step S21 with outer layer parameter and the law of similitude in boundary layer, calculate the interior layer parameter at entrance section place with outer layer parameter

Step S23. reconstructs mean parameter wherein W is weight function;

Step S24. optimizes weight function W, makes the parameter reconstructed with given parameter reaching unanimity, namely by optimizing weight function W, making minimum.

Further, the fluctuating parameter of entrance in above-mentioned steps two computing method be specially: first extract flowing fluctuating parameter from recovery section then POD resolution process is carried out to this pulsation information, ignore the high order mode of little energy, obtain new fluctuating parameter then by this fluctuating parameter resolve into interior layer parameter with outer layer parameter and the internal layer fluctuating parameter of porch is calculated by the law of similitude with outer fluctuating parameter fluctuating parameter is reconstructed again by with optimizing the weight function W obtained using the new pulsation information that the obtains fluctuating parameter as aided solving porch the aided solving schematic diagram of generation turbulent flow entry data as shown in Figure 3.

Build an aided solving example below, describe implementation procedure of the present invention in detail

(1) structure in aided solving region

In order to provide a time dependent full-blown turbulent flow entry data to LES or DNS simulation, the aided solving of a structure Boundary Layer on Flat Plate separately.The computational fields of aided solving as shown in Figure 4.Boundary condition is bottom is without slippage wall, and opening up to (z direction) upper both sides is all periodic boundary condition, and right side and top side are all flowing exit conditions.

First the inlet flow conditions ρ of aided solving is provided according to the inlet flow conditions of main simulation _∞, U _∞, p _∞, and the boundary layer nominal thickness δ of given porch _inl, boundary layer momentum thickness is θ _inl, the Reynolds number based on momentum thickness of porch is Re _θ=ρ _∞u _∞θ _inl/ μ _∞, the flow direction of computational fields, normal direction and exhibition to yardstick be taken as 12 δ respectively _inl, 4 δ _inl, 0.5 δ _inl.On computing grid, the flow direction and exhibition should ensure Δ x to uniform grid can be adopted to flow to grid ⁺=20 ~ 50, open up and should ensure Δ z to grid ⁺=10 ~ 20, normal mesh adopts non-uniform grid, requires wall ground floor grid the Δ y at boundary layer edge place ⁺=50 ~ 100.And setting up recovery cross section, for extracting the flowing information in downstream apart from the place of the 10 times of boundary layer thicknesss in entrance downstream.

(2) entrance mean parameter is given

In aided solving territory, assuming that inlet flow conditions flows through flat board, obtain Boundary Layer on Flat Plate average flow parameter by the NS equation (RANS equation) solving Reynolds average.Solve the common method that RANS equation is Fluid Mechanics Computation, those skilled in the art just can find in the pertinent texts of Fluid Mechanics Computation.

By the analog result of RANS, each sectional area calculated along flowing to divides the momentum thickness obtaining each cross section, assuming that at certain cross section x ^*the momentum thickness at place equals given momentum thickness θ _inl, then the entrance mean parameter using the flow parameter in this cross section as aided solving that is: $\begin{array}{cc}{\stackrel{\‾}{u}}_{i,\mathrm{inl}}\left(y\right)={\stackrel{\‾}{u}}_i(x^{*},y)& \end{array}{\stackrel{\‾}{T}}_{\mathrm{inl}}\left(y\right)=\stackrel{\‾}{T}(x^{*},y).$

The boundary layer nominal thickness δ at such entry condition place _inl, momentum thickness θ _inl, friction velocity u _{τ, inl}can determine.

(3) extraction of cross section parameter is reclaimed

At downstream, aided solving territory distance entrance 10 δ _inlset up one and reclaim cross section (recyclesection), extract the instantaneous flow parameter on this cross section for Boundary Layer on Flat Plate, can suppose that its flow parameter is upwards uniform in exhibition, average flow parameter on this cross section can be calculated by integration like this specific formula for calculation is:

Wherein Δ t represents step-length computing time, and subscript " n " and " n+1 " represent and walk computing time, and the mean value in former and later two moment after turbulent flow fully develops will reach unanimity, and T is the sampling time of mean value calculation.After the mean parameter distribution being recycled cross section, just can draw the fluctuating parameter reclaiming cross section.

And calculate the boundary layer nominal thickness δ in this cross section _rcy, momentum thickness θ _rcy, friction velocity u _{τ, rcy}.Also can obtain internal layer and the outer field law of similitude simultaneously:

Subscript " in " wherein and " out " represent boundary layer ectonexine parameter, u respectively _τx () is friction velocity, y ⁺, η is the normal direction dimensionless distance of boundary layer ectonexine respectively, and their definition is respectively:

$\begin{array}{ccc}{u}_{\mathrm{\τ}}=\sqrt{\frac{\mathrm{\μ}}{\mathrm{\ρ}}\frac{\∂u}{\∂y}{|}_{\mathrm{wall}}}& y^{+}=\frac{{\mathrm{yu}}_{\mathrm{\τ}}\mathrm{\ρ}}{\mathrm{\μ}}& \mathrm{\η}=\frac{y}{\mathrm{\δ}}\end{array},$

(4) the reconstruct weight function in boundary layer is optimized

The mean parameter reclaiming section boundary layer ectonexine is given in previous step with and the ectonexine law of similitude separately, the ectonexine mean parameter parameter of entrance section is calculated by this law of similitude with the method using the law of similitude to calculate entrance u speed is described for internal layer u speed.In entrance section and recovery cross section, internal layer u speed all should meet the law of similitude, so:

$\frac{{\stackrel{\‾}{u}}^{\mathrm{in}}(x_{\mathrm{inl}},y^{+})}{u_{\mathrm{\τ}}\left(x_{\mathrm{inl}}\right)}=f_u\left(y^{+}\right)=\frac{{\stackrel{\‾}{u}}^{\mathrm{in}}(x_{\mathrm{rcy}},y^{+})}{u_{\mathrm{\τ}}\left(x_{\mathrm{rcy}}\right)}$

∴ ${\stackrel{\‾}{u}}_{\mathrm{inl}}^{\mathrm{in}}\left(y^{+}\right)=\frac{u_{\mathrm{\τ},\mathrm{inl}}}{u_{\mathrm{\τ},\mathrm{rcy}}}\·{\stackrel{\‾}{u}}_{\mathrm{rcy}}^{\mathrm{in}}\left(y^{+}\right)$

Algorithm with reference to above formula can calculate the internal layer average flow parameter of porch with outer average flow parameter

Now the mean parameter of porch ectonexine can be synthesized new entrance mean parameter again by weight function W due to the development of flowing, the parameter that elective weight function constructs is inevitable and entrance given parameters is inconsistent.So, by the optimization to weight function W, make the parameter that average flow parameter is tried one's best and RANS is given constructed unanimously.Here selection of weighting function is:

$W(\mathrm{\η};a,b)=\frac{1}{2}(1+\tanh [\frac{a(\mathrm{\η}-b)}{(1-2b)\mathrm{\η}+b}]/\tanh \left(\mathrm{\α}\right))$

Wherein η is given independent variable, be the dimensionless distance of outer layer of boundary layer, and a, b is weight function W (η; A, b) design parameter, its initial value can be taken as a=4, b=0.2.So design problem is exactly solve following minimization problem, obtain optimum design parameter a, b, having designed rear a, b is exactly constant, and weight function only has an independent variable η.

(5) process of fluctuating parameter

Pulsating field downstream extraction time series out we, by carrying out POD analysis to it, obtain its basis function φ _i(x, t), (i=1...N), N is seasonal effect in time series number of samples here.Analyze the tubulence energy distribution in this N number of mode, because the energy distribution in high mode is very little, such as, before, M mode occupies 90% of gross energy, then can ignore N-M mode thereafter, so reconstruct pulsating field in a front M mode.This way fully remains the turbulence structure of large scale, have ignored the whirlpool of small scale and the whirlpool of dissipative scale.So new turbulence pulsation field can be obtained

Here, α _kthat pulsating field is at basis function φ _kon projection.

Fluctuating parameter after being decomposed by POD also resolves into inside and outside two-layer also the fluctuating parameter at entrance section place is calculated by the law of similitude its law of similitude is as follows:

The fluctuating parameter of porch is reconstructed according to the weight function W (η) optimized out

(6) synthesis of entrance instantaneous parameters

Finally the fluctuating parameter of porch and the given mean parameter of RANS are directly superposed, it can be used as the inlet boundary condition of aided solving.

The present invention after the given inlet boundary condition in aided solving territory, by solving Navier-Stokes equation, at the turbulent boundary layer that just can attain full development in aided solving region through calculating after a while.Then the turbulent flow data in exit, aided solving territory are extracted, passed to and adopt the main simulation process of LES or DNS, it can be used as the turbulent flow inlet boundary condition of main simulation.The data close to true turbulent flow of the turbulent boundary sufficient condition obtained like this, effectively can ensure authenticity and the validity of main simulation.

Coefficient given in the above embodiments and parameter; be available to those skilled in the art to realize or use of the present invention; the present invention does not limit and only gets aforementioned disclosed numerical value; without departing from the present invention in the case of the inventive idea; those skilled in the art can make various modifications or adjustment to above-described embodiment; thus protection scope of the present invention not limit by above-described embodiment, and should be the maximum magnitude meeting the inventive features that claims are mentioned.

Claims (6)

1. a turbulent flow entry data generation method, it specifically comprises the following steps: step one, obtains the mean parameter at entrance section place; Step 2, from downstream recovery cross section, extract pulsation information, after first this pulsation information being carried out the intrinsic characteristics resolution process in space, then carry out transformation of scale according to the law of similitude, then using the fluctuating parameter of result as entrance; Step 3, mean parameter and fluctuating parameter are added synthesis turbulent flow entrance instantaneous parameters.

2. turbulent flow entry data generation method as claimed in claim 1, is characterized in that described method also comprises and constructs an aided solving to generate turbulent flow entry data.

3. turbulent flow entry data generation method as described in claim 1 or 2, is characterized in that the mean parameter at the entrance section place in described step one obtained by the Reynolds average equation solving Navier-Stokes equation.

4. turbulent flow entry data generation method as claimed in claim 3, is characterized in that described step 2 also comprises the weight function design of boundary layer reconstruct.

5. turbulent flow entry data generation method as claimed in claim 4, is characterized in that the weight function design that described boundary layer reconstructs specifically comprises the following steps:

Step S21. extracts flowing instantaneous parameters from recovery section , it is averaged and obtains mean parameter , and mean parameter is decomposed into interior layer parameter in boundary layer with outer layer parameter ;

Layer parameter in step S22. obtains according to step S21 with outer layer parameter and the law of similitude in boundary layer, calculate the interior layer parameter at entrance section place with outer layer parameter ;

Step S23. reconstructs mean parameter , , wherein wfor weight function;

Step S24. optimizes weight function w, make the parameter reconstructed with given parameter reach unanimity, namely by optimizing weight function w,make minimum.

6. turbulent flow entry data generation method as claimed in claim 5, is characterized in that the fluctuating parameter of entrance in described step 2 computing method be specially: first extract flowing fluctuating parameter from recovery section , then POD resolution process is carried out to this pulsation information, ignores the high order mode of little energy, obtain new fluctuating parameter ; Then by this fluctuating parameter resolve into interior layer parameter with outer layer parameter , and the internal layer fluctuating parameter of porch is calculated by the law of similitude with outer fluctuating parameter , then the weight function will obtained with optimization wreconstruct fluctuating parameter , using the new pulsation information that the obtains fluctuating parameter as aided solving porch .