CN110848065B - Method for automatically recognizing diesel oil spray crushing process and automatically realizing spray continuous calculation - Google Patents
Method for automatically recognizing diesel oil spray crushing process and automatically realizing spray continuous calculation Download PDFInfo
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
- F02M65/00—Testing fuel-injection apparatus, e.g. testing injection timing ; Cleaning of fuel-injection apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
- F02M61/00—Fuel-injectors not provided for in groups F02M39/00 - F02M57/00 or F02M67/00
- F02M61/16—Details not provided for in, or of interest apart from, the apparatus of groups F02M61/02 - F02M61/14
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Abstract
The invention discloses a method for automatically identifying the diesel oil spray crushing process and automatically realizing continuous spray calculation, thereby automatically judging the process that a liquid film is crushed into liquid drops in the diesel oil spraying process and realizing the SD-ELSA algorithm of continuous spray calculation. The SD-ELSA algorithm takes the sphericity and the average particle diameter of a liquid phase in a calculation grid as judgment basis, uses a Lagrange method to calculate particles in a flow field, uses an Euler model to calculate the grid belonging to a continuous liquid phase in grid node information in a full flow field, and converts Euler agglomerates meeting two criteria into particles and applies the Lagrange method to calculate again. The method realizes dynamic conversion coupling of the Euler-Lagrange model, can automatically obtain complete information of a flow field discrete phase and a continuous phase, performs iterative calculation, obtains three stages of liquid column, primary crushing and secondary crushing of diesel jet, and completely expresses a diesel spraying process.
Description
Technical Field
The invention belongs to the field of diesel engine spraying characteristic research, and relates to a simulation calculation method of spraying characteristics.
Background
High-pressure diesel oil enters a cylinder of the diesel engine through jet flow of the jet hole, the diesel oil can firstly form a liquid film on the periphery of a liquid column gradually from a continuous liquid column state of an outlet in the jet flow process, and further along with the development of the jet flow, the liquid film is broken to generate liquid drops which are further broken and developed to finally form atomization. This is a process where there are regions of continuous liquid phase, transition regions where continuous and discrete phases are mixed, and a region of full droplets where all are discrete phases, along the jet direction. The existing optical test method has higher cost, and simulation calculation simulation is a main means for realizing the visual research of the diesel jet process.
In the whole diesel oil spraying process, the first spraying is in a liquid column state from the outlet of the spray hole, and the flow state is a solid cylinder at the moment; when the liquid column is sprayed out in a continuous liquid form, a liquid film can be formed at the head of the liquid column under the disturbance of external gas, and the head of the liquid column is in a mushroom shape; along with the injection of diesel oil, the edge of the liquid film generates liquid film breakage due to the unbalance of surface tension and air resistance, and the formed liquid drop is in a liquid film breakage form; meanwhile, as the amplitude of the surface wave formed on the surface of the liquid column is gradually enlarged, the broken liquid film is split into a liquid sheet and large liquid drops, primary atomization is performed at the moment, the diameter of the liquid column is narrowed, and the mushroom-shaped head is deformed; when the diameter of the large droplets exceeds a critical value, the large droplets are further broken into small droplets, the process is secondary atomization, and the length of the droplets becomes the broken length and is stably present in a spray field.
There are two ways to describe the motion of a fluid: euler (Euler) and Lagrange (Lagrange) methods. The Eulerian method focuses on determining the spatial point of a position, and the basic idea is to examine the distribution of various variables in a flow field at the same position at different moments, so that the Eulerian method is suitable for calculating a liquid column and a liquid film of a continuous phase. The Lagrange method is a discrete phase model, and the basic idea is to track the motion process of each fluid particle in the flow process, so that the method is suitable for discrete droplet calculation.
The main calculation method at present is to adopt more Lagrange (Lagrange) method, and focus on the characteristics of liquid drops in jet flow, such as DDM (distributed data modeling). When the DDM model is applied, the discrete phase of the liquid drop exists at the outlet of the jet orifice, and the equivalent diameter, the particle diameter and the average speed of the outlet of the jet orifice are required to be determined. The method is that the initial condition needs to be repeatedly iterated and tried, and the calculation method simplifies the liquid column area and the mixing area and is not in accordance with the actual atomization process. Research has begun to combine the euler and lagrange methods to assume that the region is a mixed region of a continuous phase and a discrete phase by defining a certain spatial position in the direction of injection in advance, the euler method is used from the region to the injection hole, and the lagrange method, namely the ELSA method, is used after the region, but this method is one in which the accuracy of determining the mixed space greatly affects the calculation accuracy, and the interval position cannot be changed dynamically, and is not suitable for a changing operating state when conditions such as injection pressure change.
In order to automatically realize the calculation of the spraying process when the boundary condition is changed and also automatically and continuously realize, the method dynamically identifies the process from the continuous phase of a liquid film to the discrete phase of liquid drops in the jet flow process, and takes the sphericity and the average particle diameter as judgment indexes, thereby realizing the automatic coupling of the Euler method and the Lagrange method.
Disclosure of Invention
The application of this method is to satisfy two assumptions: the liquid phase always exists in the flow field and particles can be generated in each area at any time; the particles will become gas phase but not liquid phase, i.e. the lagrange method never returns to the euler method.
In simulation calculation, only one calculation system can be applied under one grid system, so the method takes the Eulerian method as a basic system to calculate a complete flow field, takes the primary particles which accord with the criteria of sphericity and average particle diameter out of the original grid space, and covers another Lagrange calculation system on the original Eulerian method to realize the dynamic identification of the particle characteristics of the flow field, and the specific steps are as follows:
initializing a flow field to start calculation, knowing information of a continuous phase grid and discrete particles through grid node parameters, firstly judging whether particles exist in the flow field, if so, calculating the particles in the flow field by using a Lagrange method and obtaining a new state of the original particles after calculation of a KH-RT model; whether particles exist in the flow field or not, the continuous phase in the flow field is calculated and solved by an Euler method, the sphericity and the average particle diameter of the continuous liquid phase in the grid are calculated, whether particles are nascent in the flow field or not is judged by using a criterion, the fluid meeting the criterion is considered to be in a particle state, and the complete discrete phase information in the flow field is obtained by summing the fluid and the original particle phase in the flow field.
If the continuous phase fluid after the calculation by the Eulerian method does not accord with the criterion of converting into particles, no new particles are considered to be generated in the flow field, and Eulerian method calculation data, namely complete flow field continuous phase information, is output.
And integrating the continuous phase information and the discrete phase information of the flow field together to obtain and output complete flow field information, judging whether the calculation is finished or not according to whether the calculation result is converged or not, finishing the calculation if the convergence condition is met, and returning to continue iterative calculation if the convergence condition is not met.
When calculating the flow field, particles in the flow field may include three parts at most: and the continuous phase generates primary particles meeting the criterion, original particles in the flow field and new particles generated by crushing and colliding the original particles in the flow field after passing through a KH-RT model, the three particles are uniformly calculated by applying a Lagrange method, and crushing and collision polymerization are performed by applying the KH-RT model. It is clear that two lines are always calculated in each calculation, namely the Eulerian method is always used for calculating a continuous liquid phase, and newly generated particles are continuously calculated by the Lagrange method.
Two criteria for determining particle initiation, sphericity and mean particle diameter, are specified below:
the sphericity is used for judging the sphericity of fluid in the grid, the conversion into discrete phase particles in the agglomerates close to the sphericity is higher in precision, and the selection of the agglomerates based on the shape and the non-sphericity mainly follows the following equation:
wherein Sphericity is Sphericity, VpIs the volume of the particles, SpThe particle surface area is adopted, the sphericity value range is 0-1, the sphericity is 1 and represents perfect sphericity, the sphericity range of a particle phase is 0.5-1, the calculation result of Euler agglomerates in a grid is in the range, the grid is considered to be possible discrete phase particles, otherwise, a continuous liquid phase exists; taking the minimum value of 0.5 as a criterion in the method, and when the sphericity calculation result is more than 0.5, considering that the Euler agglomerate can meet the requirement of converting into particles at present, and needing to be judged by the next step of average particle diameter; for liquid lumps that do not meet the criterion for sphericity, they are considered to be present as a liquid phase.
The average particle range of the discrete particle phase is considered to be 0.01-0.05 mm, the calculation result of Euler agglomerates in the grid is considered to be the discrete phase particles in the grid in the range, otherwise, the discrete phase particles exist in a continuous liquid phase; taking the maximum value of 0.05mm as a criterion in the method, and when the diameter calculation result of the average particle diameter is less than 0.05mm, considering that the current Euler agglomerate can meet the requirement of converting into particles, and deducing the calculation formula of the average particle diameter as follows:
the liquid break-up should begin with a break-up of the liquid film, and therefore, on a time scale, the large droplets produced first result from destabilization of the liquid film break-up, mainly due to the air resistance greater than the surface tension maintaining its inner cloth, i.e.:
in the formula: p is a radical oflAnd pgjRespectively, liquid and gas pressure, v, caused by turbulencelIs the velocity component, mu, of the liquid in the transverse direction of the liquid film jetlIs the hydrodynamic viscosity coefficient, x is the displacement of the liquid film in the direction of the spray, y is the direction perpendicular to the spray of the liquid film, σlIs the surface tension of the liquid, xijIs the gas surface wave amplitude; the amplitude of the surface wave increases with time and the extension of the liquid film, and the relation between the amplitude is as follows:
ξ＝ξ0exp(ωt)
omega is angular velocity, t is time; under the action of gravity, the diameter of the liquid drop formed by the static liquid film is as follows:
σlis the surface tension of a liquid, plIs the liquid density, g is the acceleration of gravity; when the interaction between surface tension and air resistance and gravity is considered after the liquid film breaks, the formula is:
Dm1i.e. the average particle diameter, D the orifice diameter, v the liquid film velocity, σlIs the liquid surface tension, rho is the mixing density, g is the acceleration of gravity;
judging Euler agglomerates which simultaneously meet two criteria of sphericity and average particle diameter as discrete particles suitable for a Lagrange method, deleting node information belonging to a continuous liquid phase on a grid of the Euler agglomerates, covering a layer of particle information, stripping the particles meeting the criteria into a Lagrange computing system covered on the Euler computing system for recalculation, and performing next step crushing polymerization calculation on the particles by using a KH-RT model; if either of the two is not satisfied, the fluid in the grid at the moment is considered to exist as a continuous phase, and the calculation result of the Euler calculation system is reserved. This achieves a dynamic transformation of the particle generation based eulerian method to the lagrange method.
Drawings
FIG. 1 is a flow chart of the present SD-ELSA method;
fig. 2 is a schematic view of a method incorporating an atomization process.
Detailed Description
Entering the whole flow field calculation domain from the outlet of the nozzle, calculating a flow field grid in the first step, adopting a large vortex simulation method for the atomization flow field, adopting an RANS equation for near-wall processing in order to simplify the calculated amount, adopting LES simulation for a free shear layer, calculating a sub-model of the large vortex equation by using WNLES-Omega in order to reduce the calculated amount on the premise of ensuring the calculation accuracy, calculating a VOF model of a near field by using an Explicit method, and calculating a DDM model of a far field by using a KH-RT fragmentation model.
The boundary conditions and the calculation model parameters of the simulation are as follows: the inlet pressure is 100Mpa, the back pressure is 1Mpa, the diameter of the nozzle is 0.3mm, the length-diameter ratio is 5, the fluid is diesel oil, the wall temperature is 298.15K, the fluid density is 850kg/m3, the surface tension coefficient is 0.031N/m, the air is compressible gas, the air temperature is 298.15K, the sphericity is 0.5, and the average particle diameter is 0.05mm as a criterion.
Judging whether particles exist in the flow field or not, and if the particles exist, calculating the existing particles by applying a Lagrange model; when an Euler multiphase flow model is used for calculating an Euler continuous phase of the whole flow field, judging the continuous liquid phase by taking the sphericity and the average particle diameter as criteria, considering that Euler agglomerates with the sphericity larger than 0.5 and the average particle diameter smaller than 0.05mm can be converted into particles, and calculating and solving the particles and the original particles under a Lagrange system and storing particle information;
if the transformation criterion is not met, the Euler continuous phase is determined, and the calculation result under the Euler system is reserved, so that the complete calculation result of the continuous phase and the discrete phase in the flow field is obtained.
Claims (1)
1. A method for automatically recognizing diesel oil spray crushing process and automatically realizing spray continuous calculation is characterized in that:
1.1 calculating a continuous phase in the whole flow field by an Euler method, and calculating particles in the flow field by a Lagrange method;
1.2, judging whether particles are nascent or not on the Euler continuous phase, converting Euler agglomerates which meet the criterion into Lagrange particles, and recalculating by using a Lagrange method to realize dynamic conversion and coupling from the Euler method to the Lagrange method;
the criterion for judging whether the particles are nascent in the flow field is as follows:
2.1 sphericity
And (3) calculating the sphericity of the Euler agglomerates in the grid according to (1):
wherein Sphericity is Sphericity, VpIs the volume of the particles, SpIs the particle surface area;
the sphericity value range is 0-1, the sphericity is 1 and represents perfect sphericity, and when the sphericity calculation result is greater than 0.5, the current Euler agglomerate can meet the requirement of being converted into particles;
2.2 average particle diameter
For euler agglomerates within the grid, the average particle diameter was calculated according to (2):
Dm1i.e. the average particle diameter, D the orifice diameter, v the liquid film velocity, σlIs the surface tension of the liquid, ρ is the mixing density, g is the acceleration of gravity
The average particle diameter range of the discrete particle phase is considered to be 0.01-0.05 mm, and when the average particle diameter calculation result is less than 0.05mm, the Euler agglomerate at present is considered to be capable of meeting the requirement of converting into particles;
regarding Euler agglomerates which simultaneously meet two criteria of sphericity and average particle diameter as particles, deleting node information belonging to a continuous liquid phase on grids of the Euler agglomerates to generate new particle information, and stripping the particles meeting the criteria into a Lagrange computing system covered on the Euler computing system for recalculation; if either of the two is not satisfied, the fluid in the grid at the moment is considered to exist as a continuous phase, and the calculation result of the Euler calculation system is reserved.
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| CN115186570B (en) * | 2022-07-11 | 2023-07-04 | 中国人民解放军国防科技大学 | Low-cost supersonic liquid jet injection atomization numerical simulation method |
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| CN117252128B (en) * | 2023-11-17 | 2024-01-26 | 中国空气动力研究与发展中心计算空气动力研究所 | Swirl nozzle atomization process simulation method, device, equipment and storage medium |
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