CN-115544905-B - Mixed layer thickness identification method based on satellite coordinate system

Abstract

The invention discloses a mixed layer thickness identification method based on a satellite coordinate system, which comprises the steps of introducing flow field data, homogenizing the flow field data, marking a fluid domain and a non-fluid domain, identifying active flow and passive flow, respectively tracking characteristic streamline of the active flow and the passive flow, determining the boundary of a mixed region, establishing the satellite coordinate system, determining an integral path set of the mixed region, integrating all integral paths to obtain the thickness of a mixed layer of each integral path, namely obtaining the thickness of a mixed layer of the mixed region along the way, screening discrete points of the integral paths for increasing or decreasing the thickness of the mixed layer forwards and backwards, removing, drawing a graph of the thickness of the mixed layer along the flow direction, and completing the identification of the thickness of the mixed layer. The method is applied to the field of flow field mixing, can meet the calculation requirement of the thickness of the mixed layer under the condition of more general flow field, and provides more accurate data for flow field analysis, mixed supercharging evaluation and other applications.

Inventors

• XU WANWU
• ZHOU LETIAN
• YE WEI
• LI ZHIYAN
• ZHANG ZHENKANG
• JING QI

Assignees

• 中国人民解放军国防科技大学

Dates

Publication Date

20260512

Application Date

20220825

Claims (5)

1. 1. The mixed layer thickness identification method based on the satellite coordinate system is characterized by comprising the following steps of: Step 1, importing stream field data, boundary data and entry data; step 2, homogenizing the flow field data, and marking a fluid domain and a non-fluid domain in the flow field data based on boundary data, wherein the method specifically comprises the following steps: firstly, converting boundary data into a two-dimensional full 1 array with the same specification as new flow field data after interpolation, and sealing the flow field boundary by adopting a path searching mode, wherein the process comprises the following steps: setting an initial search Point ; Calculating minimum index distance between two points in boundary data And maximum index distance Obtaining the search radius of the search point as ; The search radius of the search points is overlapped in sequence from small to large each time in the search process until the position of the next point is searched, and a direction angle between the two points is obtained; then proceeding according to the current search line, carrying out data filling marking on the passing grid, namely converting the value on the search point from 1 to 0, namely converting the fluid domain into the non-fluid domain until finishing updating the boundary data, and obtaining a continuous closed non-fluid domain boundary in the array; Secondly, marking the fluid domain and the non-fluid domain by taking the non-fluid domain boundary as a limit, and correcting the flow field data subjected to homogenization treatment by taking the generated marked non-fluid domain as a constraint, so that the flow field is smoother; Step3, identifying an active flow and a passive flow in the flow field data based on the inlet data, respectively tracking characteristic streamline of the active flow and the passive flow, and determining the boundary of the mixing area; step 4, a satellite coordinate system is established based on the streamline, and an integral path set of the mixing area is determined according to the satellite coordinate system; And 5, mapping flow field data of each integral path on the integral path set to a data space, and integrating all the integral paths to obtain the thickness of a mixed layer of each integral path, namely the thickness of an along-path mixed layer of a mixed region, wherein the thickness of the mixed layer of each integral path is obtained by integrating all the integral paths, specifically: The thickness of the mixed layer is as follows in Cartesian coordinates: In the formula, For the mixed layer thickness, C is the integral coordinate independent term, Is a subject item; Mapping the thickness of the mixed layer from Cartesian coordinates to a q 1 oq 2 coordinate system is: In the formula, Representing Mapping from Cartesian coordinates to A coordinate system; Performing discrete processing on the above materials, wherein the discrete processing comprises the following steps: Where point (k) represents the kth discrete point on the corresponding integration path, num represents the number of discrete points included in the corresponding integration path, dr represents the spacing between the discrete points on the corresponding integration path; step 6, screening out discrete points of an integral path for increasing or reducing the thickness of the mixed layer forwards and backwards or abnormality according to the consistency of the thickness calculation result of the mixed layer in the same mixed region and removing the discrete points; and 7, drawing a graph of the thickness of the mixed layer along the flow direction, and completing the identification of the thickness of the mixed layer.
2. 2. The method for identifying thickness of mixed layer based on satellite coordinate system according to claim 1, wherein in step 2, the homogenization treatment is performed on the flow field data, specifically: uniformly distributing flow field data on data nodes under the same uniform grid set through an interpolation method.
3. 3. The method for identifying thickness of mixed layer based on random body coordinate system according to claim 1, wherein in step 3, the identifying active flow and passive flow in the flow field data based on the inlet data specifically comprises: and identifying active and passive flows according to the total pressure of each inlet of the flow field, wherein the total pressure is high and is active, and the passive flow is reverse.
4. 4. A method for identifying thickness of a mixed layer based on a satellite coordinate system according to claim 1,2 or 3, wherein in step 3, the characteristic streamline of the active flow and the passive flow is tracked, and the boundary of the mixed region is determined, specifically: according to the identified active flow and passive flow, finding the standard point of the data group center corresponding to each jet flow, and tracking the streamline emitted by the standard point: According to the flow line direction, the flow field direction of the flow field is always the flow field direction, for a uniform and discrete flow field data-two-dimensional array, the flow field data and the speed angle of the kth discrete point (k) on the standard point along-path development flow line are obtained by interpolation according to the adjacent grid node data, and the flow field data of the kth (k+1) discrete point (k+1) can be calculated until the characteristic flow line mark of the standard point is completed; The region between the characteristic streamline of the active flow and the passive flow standard point is the mixing region, and the characteristic streamline of the active flow and the passive flow standard point is the upper and lower boundary of the corresponding mixing region.
5. 5. The method for identifying thickness of a hybrid layer based on a satellite coordinate system according to claim 4, wherein step 4 specifically comprises: Establishing a satellite coordinate system q 1 oq 2 , wherein the q 1 direction is a streamline direction, and the q 2 direction is the orthogonality of the q 1 direction, and determining the direction according to a right-hand rule; Taking the q 2 direction or the reverse q 2 direction as a direction integral path of the integral path, and interpolating by utilizing grid node data of the flow field to obtain flow field data and direction angles of each discrete point on the current integral path; iterating forward according to the direction angle of each discrete point on the current integral path And cycling the process until the acquisition of all integral paths of the mixed area is completed, namely determining an integral path set for identifying the thickness of the mixed layer.

Description

Mixed layer thickness identification method based on satellite coordinate system Technical Field The invention relates to the technical field of flow field mixing in fluid mechanics, in particular to a mixed layer thickness identification method based on a satellite coordinate system. Background The thickness of the mixing layer of the ejector, the combined engine and the like is a typical assessment index of the mixing effect, so that the identification of the thickness of the mixing layer plays an important role in the evaluation of the mixing efficiency, and the mixing process is a typical jet mixing process under the conditions of unparallel speed and unmatched static pressure. At present, the mixing process is studied, and most of them are in a pressure-matched state. Mixed layer thickness is typically described in terms of speed mixed layer, momentum mixed layer, vorticity mixed layer, and pressure mixed layer definitions. Because the speed type mixed layer depends on the similarity of the along-path speed profiles of the mixed layer, when the mixed layer is in a pressure matching state, an active flow (primary flow or high-speed flow) and a passive flow (secondary flow or low-speed flow) are in parallel flow when being initially mixed, no speed dip angle exists, and the along-path development of the speed type profile of the mixed layer under a Cartesian coordinate system can be well ensured to be similar to each other, so that the thickness of the mixed layer can be well defined by describing the thickness of the mixed layer based on the Cartesian coordinate system by using the traditional method, and a good result can be obtained. The method for defining the thickness of the mixed layer mainly comprises the following steps: 1. Average velocity thickness δ b —considering the velocities of the high velocity layer and the low velocity layer as U 1 and U 2, respectively, the velocity difference is Δu=u 1-U2, the velocity thickness may be defined as δ b＝yU0.9-yU0.1, where y U0.9 and y U0.1 are the lateral positions at the corresponding velocities, here U 0.9＝U1-0.1ΔU,U0.1＝U1 +0.1Δu. 2. Brown & Roshko proposed in 1974 a vortex thickness δ ω of: the normal momentum conservation equation is integrated to obtain: Wherein, the Y max is corresponding toIs a position of (2); bringing formula (2) into formula (1) yields: 3. The momentum thickness δ θ as shown in fig. 1 is: The three speed type hybrid layer thickness definitions described above are basically based on the speed type hybrid layer definition. The thickness of the various definition mixed layers based on the speed is described by using a traditional Cartesian coordinate system, and when the pressure matching mixing of the active flow and the passive flow is described, namely, the parallel flow mixing is performed, the speed profile development is similar to each other along the path, so that a good result can be obtained. However, when the mixed layer thickness is calculated by using the definition in Cartesian coordinates, particularly based on the velocity type, the mixed layer thickness is not suitable, and as shown in FIG. 2, the typical active and passive flows have significant velocity angles for mixing. At the same time, coupling effects such as expansion and compression exist in the mixing process, so that the speed profile of the mixing area is not full like the speed profile shown in fig. 1, but is cluttered without specific speed, and therefore the speed profile in the non-parallel mixing area does not have self-similar characteristics along the change of coordinates. Whereas the conventional hybrid layer thickness identification was initially assumed to control the in vivo velocity parallelism, the along-the-path velocity profiles were similar to each other, it was found in fig. 2 that the along-the-path hybrid layer velocity profiles were irregular and dissimilar to each other, and that there was a non-negligible velocity component along the normal of the coordinates, thus resulting in a very inaccurate description of the velocity-type defined hybrid layer thickness under the coordinate system. In particular, for a complex flow structure such as a vortex structure, as shown in fig. 3, the velocity profile of the complex flow structure has no similarity along the path, and the hybrid layer definition based on the velocity is more difficult to adapt under the cartesian coordinate system, so that the reliability of the calculation result cannot be guaranteed. In view of this, the reliability of the results of the speed type hybrid layer identification based on the cartesian coordinate system is not high in the mixing in the non-matching state, the mixing in the limited space, the mixing in the coupled state with shock expansion, and the like. Referring to fig. 4-6, the thickness development curve of three speed type mixed layers of the mixing area of the four-support plate ejector in a Cartesian coordinate system is shown, and the pressur