Angular momentum transfer-based rotational flow state analysis method

Abstract

The invention belongs to the technical field of aero-engines, and particularly relates to a rotational flow state analysis method based on angular momentum transfer, which comprises the following steps: acquiring structural parameters of a hydrocyclone and a contraction channel, comprise a ring surface inner radius of a blade channel outlet section, a ring surface outer radius of the blade channel outlet section, a ring surface inner radius of a throat section, a ring surface outer radius of the throat section, a blade angle theta and a pitch angle of the throat section; based on a mass conservation equation and an angular momentum conservation equation, the rotational flow state of the blade channel outlet section serves as an initial value, and the rotational flow number SN2 and the airflow deflection angle beta of the throat section are calculated. The influence of structural parameters of the swirler and the contraction channel on flowing is integrated; the rotational flow state at the outlet of the head is represented and is closer to the top dead center of the flame root / backflow area, and more information influencing the combustion structure can be disclosed.

Description

Technical Field

[0001] This application belongs to the field of aero-engine technology, and specifically relates to a swirling state analysis method based on angular momentum transfer. Background Technology

[0002] The combination of a swirler (using fixed blades to deflect airflow, causing it to rotate axially) and a contraction channel is a mature and widely used combustion head structure in the field of main combustion chambers. It uses a swirling-contraction-expansion flow to create a recirculation and flame-stabilizing structure in the main combustion zone, forming a stable flame root. Designers typically use swirling numbers... This dimensionless parameter characterizes the swirling intensity at the outlet section of the cyclone blade channel to guide cyclone design. However, the design of the contraction channel structure is often studied separately, focusing on its contraction section length and contraction area ratio, which is relatively isolated from the cyclone design and lacks an effective correlation. A method is needed to integrate and predict the influence of these two structures on flow, thereby improving the efficiency of the initial one-dimensional design of the main combustion chamber head structure and reducing the number of iterations.

[0003] The traditional method for calculating the downstream swirl number is to calculate the swirl number at the blade passage exit section based on structural parameters such as the swirler blade angle and inner / outer diameter. This method only reflects the influence of swirler structural parameters on the flow; it can only characterize the swirl state at the swirler exit and is difficult to directly correlate with combustion organization, so it can only be used as one of the influencing factors for qualitative analysis. It is relatively accurate in predicting the swirl number for simple structures, but the accuracy decreases as the subsequent flow structure of the swirler becomes more complex.

[0004] The traditional method for calculating the downstream airflow deflection angle is to directly use the cyclone blade angle as the airflow deflection angle. This only reflects the influence of the cyclone blade angle on the flow, and its reference value is limited. Furthermore, its prediction of the airflow deflection angle is inaccurate. Summary of the Invention

[0005] To address the aforementioned problems, this application provides a swirling flow state analysis method based on angular momentum transfer, comprising:

[0006] Obtain the structural parameters of the hydrocyclone and the contraction channel, including the inner radius of the torus of the blade channel outlet section. Outer radius of the torus of the blade passage exit section Inner radius of the throat section Outer radius of the throat section Blade angle θ and throat section pitch angle ;

[0007] Based on the mass conservation equation and the angular momentum conservation equation, using the swirl state at the blade passage exit section as the initial value, the swirl number S at the throat section is calculated.N2 Airflow deflection angle β.

[0008] Preferably, the mass conservation equation is:

[0009] ;

[0010] Let be the axial velocity at the blade passage exit section. denoted as axial velocity of the throat section.

[0011] Preferably, the equation for the conservation of angular momentum is:

[0012] ;

[0013] The tangential velocity at the blade passage exit section is... The tangential velocity is the velocity of the throat cross section.

[0014] Preferably, the swirl number S of the throat cross section is... N2 The calculation formula is:

[0015] .

[0016] Preferably, the number of swirls at the channel outlet cross-section is [missing information]. The calculation formula is:

[0017] .

[0018] Preferably, the formula for calculating the airflow deflection angle at the throat section is:

[0019] .

[0020] Preferably, the swirling state analysis method based on angular momentum transfer is based on simplified assumptions, including: the fluid is incompressible and the density ρ is constant; the velocity distribution is two-dimensional, considering only the axial and tangential components and ignoring the radial velocity; the velocity is uniform on the same cross section; and the airflow deflection angle at the blade passage outlet is consistent with the blade angle.

[0021] For calculating the downstream swirl number at the head, this invention uses the swirl state at the blade passage exit section as an initial value, based on mass conservation, to calculate the swirl number at the throat section. It integrates the influence of the structural parameters of the swirler and the converging channel on the flow; it characterizes the swirl state at the head exit, is closer to the top dead center at the flame root / recirculation zone, and can reveal more information affecting combustion organization. Regarding prediction accuracy, compared to traditional methods that are only applicable to simple structures, this invention can accurately predict the downstream swirl number for various complex head structures.

[0022] For calculating the downstream airflow deflection angle at the head, this invention uses the swirling state at the blade channel exit section as an initial value, based on the conservation of mass and angular momentum, to calculate the airflow deflection angle at the throat section. It integrates the influence of the structural parameters of the swirler and the converging channel on the flow; characterizing the swirling state at the head outlet, it is closer to the top dead center of the flame root / recirculation zone, enabling a quantitative assessment of the radial expansion caused by the centrifugal force of the swirling airflow there, and thus relating it to key physical processes such as large-scale eddies, oil-gas coupling, and root flame ignition. In terms of prediction accuracy, compared to traditional methods that only qualitatively characterize the airflow deflection angle through the swirler blade angle, this invention provides a more accurate prediction of the airflow deflection angle and can be used for quantitative analysis. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the geometric parameters of the tri-swirl head. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are only some, not all, of the embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings. Figure 1 As shown, 1. Structural parameters:

[0025] The geometric parameters of the three-swirl head involved in the calculation are shown in the figure below. The thick green solid line represents the exit section of each blade channel (section 1), and the thick red solid line represents the throat section of each stage (section 2). Taking the first-stage channel as an example, the inner and outer radii of the torus of section 1 are... , The inner and outer radii of the torus of section 2 , And the pitch angle of the throat section The diagram illustrates this. The structural parameters for the second and third level channels are defined in the same way as those for the first level throat.

[0026] 2. Description of physical quantities:

[0027] a) Mass flow rate:

[0028] (1)

[0029] b) Axial momentum flux:

[0030] (2)

[0031] c) Axial flux of angular momentum:

[0032] (3)

[0033] d) Swirl number:

[0034] (4)

[0035] 3. Simplify assumptions:

[0036] Incompressibility:

[0037] That is, the air density under study It does not change with spatial location.

[0038] a) The two-dimensionality of velocity:

[0039] This means that the velocity is assumed to have only two directional components: axial (absolute axial or custom direction) and tangential (circumferential tangential direction), without considering the radial velocity component.

[0040] b) One-dimensionality of velocity distribution:

[0041] This means that the spatial distribution of axial and tangential velocities is considered to depend only on the axial position (different cross-sections upstream and downstream), and is independent of the radial position (distance r from the central axis on the same cross-section) and the circumferential position (i.e., positions corresponding to different central angles). In other words, the axial and tangential velocities are uniformly distributed on each research cross-section.

[0042] c) Assume that the actual deflection angle of the airflow at the outlet of the cyclone separator blade passage is the same as the blade angle, that is:

[0043] (5)

[0044] d) Based on the above simplified assumptions, the axial momentum flux Axial flux of angular momentum It can be transformed into:

[0045] (6)

[0046] (7)

[0047] e) It is assumed that the axial and tangential velocities at the blade passage exit are the same as those inside the blade passage, i.e., the influence of blade thickness is ignored (if this influence needs to be considered, then U in the following text should be multiplied by a coefficient). )

[0048] 4. Governing equations:

[0049] a) Continuity equation (mass conservation equation):

[0050] (9)

[0051] b) Equation for conservation of angular momentum:

[0052] (10)

[0053] Note: The axial velocity of the throat section in the above formula... The absolute axial velocity should be used, not the normal of the custom throat section. If a custom axial velocity is used, then... Multiplied by a coefficient .

[0054] 5. Calculation of throat swirl number and airflow deflection angle:

[0055] Based on the above governing equations and simplifying assumptions, the swirl number and airflow deflection angle at the throat cross-section can be calculated.

[0056] a) Swirl number (geometric swirl number) at the blade passage exit section:

[0057] (11)

[0058] b) Swirl number at throat cross section:

[0059] (12)

[0060] c) Airflow deflection angle at the throat section:

[0061] (13);

[0062] This application calculates the downstream swirl number at the head by using the swirl state at the blade passage exit section as an initial value based on mass conservation. This yields the swirl number at the throat section. It integrates the influence of the structural parameters of the swirler and converging channel on the flow; it characterizes the swirl state at the head exit, more closely approximating the top dead center at the flame root / recirculation zone, and can reveal more information affecting combustion organization. Regarding prediction accuracy, compared to traditional methods that are only applicable to simple structures, this invention can accurately predict the downstream swirl number for various complex head structures.

[0063] For calculating the downstream airflow deflection angle at the head, this invention uses the swirling state at the blade channel exit section as an initial value, based on the conservation of mass and angular momentum, to calculate the airflow deflection angle at the throat section. It integrates the influence of the structural parameters of the swirler and the converging channel on the flow; characterizing the swirling state at the head outlet, it is closer to the top dead center of the flame root / recirculation zone, enabling a quantitative assessment of the radial expansion caused by the centrifugal force of the swirling airflow there, and thus relating it to key physical processes such as large-scale eddies, oil-gas coupling, and root flame ignition. In terms of prediction accuracy, compared to traditional methods that only qualitatively characterize the airflow deflection angle through the swirler blade angle, this invention provides a more accurate prediction of the airflow deflection angle and can be used for quantitative analysis.

[0064] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for analyzing the swirling state based on angular momentum transfer, characterized in that, include: Obtain the structural parameters of the hydrocyclone and the contraction channel, including the inner radius of the torus of the blade channel outlet section. Outer radius of the torus of the blade passage exit section Inner radius of the throat section Outer radius of the throat section Blade angle θ and throat section pitch angle ; Based on the mass conservation equation and the angular momentum conservation equation, using the swirl state at the blade passage exit section as the initial value, the swirl number S at the throat section is calculated. N2 Airflow deflection angle β.

2. The swirling state analysis method based on angular momentum transfer as described in claim 1, characterized in that, The mass conservation equation is: ； Let be the axial velocity at the blade passage exit section. denoted as axial velocity of the throat section.

3. The swirling state analysis method based on angular momentum transfer as described in claim 2, characterized in that, The equation for the conservation of angular momentum is: ； The tangential velocity at the blade passage exit section is... The tangential velocity is the velocity of the throat cross section.

4. The swirling state analysis method based on angular momentum transfer as described in claim 3, characterized in that, Swirl number S at the throat cross section N2 The calculation formula is: 。 5. The swirling state analysis method based on angular momentum transfer as described in claim 3, characterized in that, Channel outlet cross-section swirl number The calculation formula is: 。 6. The swirling state analysis method based on angular momentum transfer as described in claim 3, characterized in that, The formula for calculating the airflow deflection angle at the throat section is: 。 7. The swirling state analysis method based on angular momentum transfer as described in claim 3, characterized in that, The swirling state analysis method based on angular momentum transfer is based on simplified assumptions, including: the fluid is incompressible and the density ρ is constant; the velocity distribution is two-dimensional, considering only the axial and tangential components and ignoring the radial velocity; the velocity is uniform on the same cross section; and the airflow deflection angle at the blade passage outlet is consistent with the blade angle.

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