Method for evaluating uniformity of outlet flow field of integrated composite flow channel of combustion chamber and turbine guider

Abstract

The invention discloses a combustion chamber and turbine guider integrated composite flow channel outlet flow field uniformity evaluation method, and belongs to the technical field of gas turbine pneumatic design. The method comprises the steps that a geometric model of a combustion chamber and turbine guider integrated composite flow channel is built, a combustion chamber function section and a guider pneumatic section are fused through integral pneumatic modeling to form a continuous flow channel, a front section adopts a diffusion structure to form a low-speed combustion area, and a rear section adopts a gradually-shrinking channel to achieve gas accelerated expansion; performing three-dimensional cold-state flow field numerical simulation by adopting a structured grid division and delay separation vortex simulation technology; flow parameters including total pressure, Mach number, airflow angle and vorticity are extracted from the cross section of a flow channel outlet, conversion from a Cartesian coordinate system to a polar coordinate system is carried out, and a uniformly distributed aerodynamic parameter field is reconstructed by using an interpolation algorithm; the directional coupling degree is calculated based on the spatial correlation of the pressure gradient vector and the vorticity vector, and the vortex-pressure coupling entropy production index representing the overall aerodynamic loss of the flow channel is established in combination with the pressure pulsation intensity and the vorticity concentration ratio. According to the method, a three-dimensional evaluation system is constructed by integrating circumferential and radial non-uniformity and entropy production parameters, and accurate quantitative evaluation of flow characteristics and uniformity of the combustion chamber and turbine integrated structure is realized.

Description

Technical Field

[0001] This invention belongs to the field of ground-based heavy-duty gas turbine technology. Specifically, it is a method for evaluating the uniformity of the flow field at the outlet of an integrated composite flow channel combining a combustion chamber and a turbine guide. Background Technology

[0002] Traditional gas turbine combustors and turbine guide vanes are designed as separate units, connected structurally and aerodynamically by a transition section. This transition section, as an independent functional component, simultaneously undertakes the tasks of guiding high-temperature gas flow, maintaining pressure, and providing structural support. It can improve the uniformity of the flow field at the combustor outlet to some extent and optimize the flow conditions to the guide vane by controlling the pressure gradient, reducing angle-of-attack deviation and unsteady effects. However, the geometric discontinuity of the separate design leads to complex secondary flow effects. Combined with horseshoe vortices and corner separation in the end-face region, this generates additional entropy increase, exacerbating circumferential temperature distortion in the flow field and thus affecting the isentropic efficiency of the turbine stage. While this structure offers advantages in modular maintenance, it has inherent defects in aerodynamic and thermodynamic performance. Computational fluid dynamics (CFD) analysis shows that flow separation at the connection between the transition section and the guide vane can lead to a total pressure loss of up to 3-5%, and this loss increases non-linearly as the operating conditions deviate from the design point. In addition, when the high-temperature gas at the combustion chamber outlet passes through the transition section, due to the local flow stagnation effect, periodic hot spots will form at the leading edge of the guide vane, causing the turbine blades to be subjected to asymmetric thermal loads and affecting their fatigue life.

[0003] From an aerodynamic perspective, the interaction between the secondary flow and the mainstream in a split-type structure creates a localized high-temperature disturbance layer, significantly altering the boundary layer thermodynamic state and exacerbating mixing losses. More significantly, the split structure causes the combustor outlet flow field characteristics and the guide vane profile to couple only under specific operating conditions. When deviating from the design point, this easily generates a reverse pressure gradient, inducing boundary layer separation and dynamic flow instability. These characteristics essentially reflect the inherent contradiction between local flow field control and system-level flow quality in split-type designs. Furthermore, the mechanical connection gap between the transition section and the guide vane can lead to high-temperature gas leakage, forming a localized jet that interferes with the mainstream flow. Although this leakage flow accounts for less than 0.2% of the mass flow rate, its temperature is 100-150K higher than the mainstream, creating a significant temperature gradient at the guide vane inlet and further deteriorating the flow field quality. Eliminating the transition section and constructing an integrated device that combines the combustor and turbine guide vane can achieve a seamless transition from the combustor outlet to the guide vane inlet in terms of flow channel morphology. This integrated configuration will become a key technological path for improving gas turbine efficiency.

[0004] The evaluation of gas turbine combustor outlet airflow uniformity is primarily based on the temperature field, with the overall temperature distribution factor (OTDF) as the core indicator, quantifying the degree to which the highest total temperature point deviates from the average temperature rise. Radial and circumferential temperature distribution factors (RTDF and CTDF) respectively analyze the downstream blade root-to-tip temperature gradient and the periodicity of circumferential thermal load, and are further combined with velocity distribution factors to characterize aerodynamic mismatch and quantify the degree of non-uniformity of the outlet velocity field. The turbine guide vane outlet flow field directly affects the aerodynamic performance, thermal load, and lifespan of the downstream turbine blades. The uniformity of the outlet flow field is typically evaluated using parameters such as the total pressure loss coefficient, outlet airflow angle distribution, outlet Mach number, or velocity distribution. However, these traditional evaluation systems have significant limitations: OTDF only reflects extreme temperature deviations and cannot characterize the overall field distribution characteristics; while RTDF and CTDF can analyze radial and circumferential gradients, they neglect the coupling effect between the temperature and velocity fields. More importantly, the integrated combustion chamber and turbine guide vane unit utilizes continuous profile curvature reconstruction technology to smoothly enclose the blade profile, forming a continuous flow channel encompassing both the combustion chamber functional section and the guide vane aerodynamic section. The front section forms a low-speed combustion zone to enhance the enthalpy energy of the combustion gas, while the rear section forms an expansion acceleration zone to convert this energy into mechanical energy, achieving integrated fusion of the combustion chamber and turbine guide vane. This unique integral, continuous flow channel completely eliminates the physical interface of traditional split designs, allowing the conversion of thermal and kinetic energy to occur continuously in space. This renders traditional indicators for evaluating the uniformity of the combustion chamber outlet and guide vane outlet inapplicable. Therefore, it is necessary to construct an evaluation index system that reflects the uniformity of the outlet flow field throughout the entire process from combustion to expansion acceleration in the integrated configuration, providing a basis for the aerodynamic optimization design of the integrated combustion chamber and turbine guide vane composite flow channel. Summary of the Invention

[0005] To address the above problems, this invention proposes a method for evaluating the uniformity of the outlet flow field in an integrated combustor and turbine guide vane flow channel. The core features of this evaluation method include: cold-state DDES (Delayed Separated Vortex Simulation) numerical simulation of the integrated combustor and turbine guide vane flow channel; reconstruction of key parameters of the outlet cross-section flow field; and vortex-pressure coupling entropy production index.

[0006] The objective of this invention is achieved as follows:

[0007] A geometric model of an integrated composite flow channel for the combustion chamber and turbine guide vane was constructed. Using a method of integral molding and local refinement, the hub profile, casing profile, and the pressure and suction profiles of the guide vane (excluding the leading edge) were smoothly enclosed to form a continuous flow channel containing the functional section of the combustion chamber and the aerodynamic section of the guide vane. The front section forms a low-speed combustion zone to increase the enthalpy energy of the combustion gas, while the rear section forms an expansion acceleration zone to convert it into mechanical energy, achieving the integrated fusion of the turbine guide vane and the combustion chamber. A structured mesh and the high-fidelity analytical model DDES were used to conduct cold-state flow field numerical simulations of the main flow channel of this integrated device.

[0008] The airflow parameters at the outlet section of the integrated combustion chamber and turbine guide vane are derived in the form of "spatial points + physical quantities," namely, "spatial Cartesian coordinates (x, y, z) + physical quantities (total pressure at the outlet section, Mach number, etc.)," ​​where the x, y, and z coordinates are the spatial coordinates of the grid nodes on the outlet control surface. In the z-plane (i.e., the outlet section), the xy rectangular coordinates are transformed into r-θ polar coordinates, and the airflow uniformity is evaluated by the radial (r direction) and circumferential (θ direction) distribution of physical quantities. The structured grid characteristics indicate that the data points are uniformly distributed in the circumferential direction (i.e., the θ direction), while the radial (r direction) distribution is non-uniform due to the refinement of the boundary layer grid. Therefore, interpolation is performed along the radial height to obtain uniformly distributed data points. The number of interpolated data points is the same as the number of grid topology nodes, ensuring that the data resolution is comparable to the original data, realizing the outlet section Mach number Ma(x, y, z), airflow angle β2(x, y, z), and total temperature T. t The flow field is reconstructed using three aerodynamic parameters (x, y, z), and the uniformity and dispersion of the outlet flow field are obtained by mass-weighted averaging and standard deviation.

[0009] Total pressure p at the outlet section t Given (x, y, z) and vorticity ω(x, y, z), calculate the vortex-pressure coupling entropy production index:

[0010]

[0011] The vortex-pressure coupling entropy production index comprehensively reflects the directional coupling degree C. d Pressure pulsation intensity σ p and vorticity concentration Ω c This method quantifies the spatial correlation between pressure gradient and vortex vector, total pressure fluctuation energy, and local high vortex intensity regions. This parameter identifies high-loss regions through vortex-pressure coupling, introduces pressure pulsation intensity to quantify dynamic distortion, and can predict hot-state risks based on cold-state simulation. It can serve as an evaluation index for the uniformity of the outlet flow field in integrated combustor and turbine guide vane flow channels.

[0012] The beneficial effects of this invention are:

[0013] The proposed method for evaluating the uniformity of the outlet flow field in an integrated combustion chamber and turbine guide vane configuration, through a comprehensive evaluation of Mach number distribution uniformity and airflow angle distribution uniformity, reflects the aerodynamic efficiency of the entire continuous expansion and acceleration process, ultimately providing inlet flow field quality for the downstream turbine rotor blades. Employing a vortex-pressure coupled entropy production index, combined with three-dimensional vorticity field analysis, it can accurately quantify the overall aerodynamic loss characteristics of the flow channel. This index comprehensively considers secondary flow losses, endwall losses, and mainstream losses, providing more comprehensive data support for the aerodynamic optimization design of the integrated combustion chamber and turbine guide vane configuration. Attached Figure Description

[0014] Figure 1 This is a process for evaluating the uniformity of the outlet flow field of an integrated composite flow channel for combustion chamber and turbine guide vane based on flow field information reconstruction and vortex-pressure coupling entropy production index. Detailed Implementation

[0015] This invention achieves flow field characteristic analysis and uniformity evaluation of an integrated composite flow channel combining the combustion chamber and turbine guide vane through the following technical process: The specific implementation steps are as follows:

[0016] 1. Geometric modeling of the integrated composite flow channel for combustion chamber and turbine guide vane

[0017] A continuous flow channel structure is constructed using a modeling method that combines integral molding with local fine-tuning. The axial curvature of the hub and casing surfaces is defined based on NURBS curves. A curvature radius is set in the combustion chamber functional section (front section) to create a low-speed combustion zone and enhance the accumulation of internal enthalpy in the combustion gases. A tapered profile design is used in the guide vane aerodynamic section (rear section) to reduce the flow channel cross-sectional area and promote expansion acceleration. The guide vane pressure and suction surfaces, with their leading edge structures omitted, are seamlessly connected to the combustion chamber wall through the principle of curvature continuity, satisfying first-order derivative continuity at the interface. This ultimately forms a continuous flow channel that integrates combustion and aerodynamic expansion.

[0018] 2. Numerical simulation methods

[0019] Three-dimensional cold-state flow field analysis was conducted using structured meshing and delayed separated eddy simulation (DDES). An H-shaped topological structured mesh was used in the main flow channel region, with 15 prismatic mesh layers near the wall boundary layer, ensuring the first mesh layer height y+ ≤ 1 and expansion ratio 1.2. The DDES method based on the SST k-ω model was employed, with the time step determined by a CFL number ≤ 1.0. The inlet boundary conditions for the integrated combustion chamber and turbine guide vane flow channel were set as total temperature and total pressure, while the outlet boundary condition was static pressure.

[0020] 3. Flow field reconstruction and uniformity quantitative evaluation at the outlet section

[0021] Aerodynamic parameters of the grid nodes are extracted at the outlet section (z = constant). The coordinates of each node are recorded in Cartesian coordinates (x, y, z), and the physical quantities of total pressure pt, Mach number Ma, airflow angle β2, total temperature Tt, and vorticity ω are output simultaneously. The xy-plane rectangular coordinates are converted to polar coordinates (r, θ). Based on the radial node distribution characteristics, cubic spline interpolation is used along the radius r to recompile the non-uniformly distributed original data, ensuring that the radial interpolation point density is consistent with the circumferential θ distribution. Original data points at 1° intervals in the circumferential direction are retained to maintain their periodic distribution characteristics. Finally, the homogenized data field of the outlet section is reconstructed, with the total number of nodes consistent with the original grid topology. The arithmetic mean and standard deviation are calculated to obtain the uniformity and dispersion of the outlet Mach number and airflow angle.

[0022] 4. Entropy production index η of eddy-pressure coupling vp calculate

[0023] Quantitative evaluation of flow field uniformity and energy loss characteristics based on derived data. Calculation of directional coupling degree C. d Pressure pulsation intensity σ p and vorticity concentration Ω c These three parameters are used to quantify the spatial correlation between pressure gradient and vortex vector, total pressure fluctuation energy, and to identify local high vortex intensity regions. A vortex-pressure coupling entropy production index is constructed using these three parameters to comprehensively reflect dynamic distortion energy, vortex intensity concentration, and pressure-vortex coupling effect. A larger index value indicates higher flow loss.

[0024] Directional coupling C d for:

[0025]

[0026] Pressure pulsation intensity σ p for:

[0027]

[0028] vorticity concentration Ω c for:

[0029]

[0030] vortex-pressure coupling entropy production index η vp for:

[0031]

[0032] This implementation method uses a closed-loop technical solution encompassing geometric modeling, numerical simulation, data processing, and comprehensive evaluation to scientifically verify the aerodynamic performance of the integrated composite flow channel of the combustion chamber and turbine guide vane, providing a reliable quantitative basis for gas turbine design.

Claims

1. A method for evaluating the uniformity of the outlet flow field in an integrated composite flow channel combining a combustion chamber and a turbine guide vane, characterized in that, Includes the following steps: (a) Construct a geometric model of an integrated composite flow channel for the combustion chamber and turbine guide vane. Through integral molding and local fine finishing, smoothly enclose the hub profile, casing profile, and guide vane pressure and suction surfaces without leading edge to form a continuous flow channel containing the combustion chamber functional section and the guide vane aerodynamic section. The front section forms a low-speed combustion zone, and the rear section forms an expansion acceleration zone. (b) The flow channel is divided using a structured grid, and a three-dimensional cold flow field numerical simulation is performed based on Delayed Separated Eddy Simulation (DDES). (c) Extract the Cartesian coordinates (x,y,z) of the spatial nodes and the physical quantities of total pressure, Mach number, airflow angle and vorticity from the outlet control surface. Convert the xy plane of the Cartesian coordinate system to the r-θ polar coordinate system. Generate uniformly distributed data points through radial interpolation and reconstruct the homogenized flow field parameters of Mach number, airflow angle and total temperature. (d) Based on the total pressure field p t Given (x,y,z) and the vorticity field ω(x,y,z), calculate the vortex-pressure coupling entropy production index η. vp This index comprehensively measures the directional coupling degree C. d Pressure pulsation intensity σ p and vorticity concentration Ω c .

2. The method according to claim 1, characterized in that: In step (a), the axial curvature of the hub profile and the casing profile is defined by the NURBS curve; The combustion chamber functional section is designed with a diffuser curvature to form a low-speed combustion zone, while the guide aerodynamic section adopts a tapering profile to form an expansion acceleration zone. The pressure surface and suction surface of the guide vane and the combustion chamber wall satisfy the continuity of the first derivative at the interface.

3. The method according to claim 1, characterized in that: In step (b), the structured mesh has at least 15 prism layers in the near-wall boundary layer, and the height of the first layer satisfies y. + ≤1, mesh expansion ratio is 1.2; The DDES method is based on the SST k-ω model, and the time step is determined with the number of CFLs ≤ 1.

0.

4. The method according to claim 1, characterized in that: In step (c), the radial interpolation uses cubic spline interpolation, while the original data points are retained at 1° intervals in the circumferential direction. The reconstructed homogenized flow field parameters include Mach number Ma, airflow angle β2, and total temperature T. t The uniformity and dispersion are quantified by the quality-weighted average and standard deviation.

5. The method according to claim 1, characterized in that: In step (d), the directional coupling degree C d The calculation formula is: Pressure pulsation intensity σ p The calculation formula is: vorticity concentration Ω c The calculation formula is: vortex-pressure coupling entropy production index η vp The calculation formula is:

6. The method according to claim 1, characterized in that: Directional coupling C d The calculation employs a normalized form of the dot product of vorticity and pressure gradient vector, reflecting the spatiotemporal correlation between secondary flow vortices and pressure distortion. The vortex-pressure coupling entropy production index η... vp It is used to quantify the dynamic distortion energy of the flow field, the concentration of vorticity, and the pressure-vorticity coupling effect. The larger the index value, the higher the flow loss.

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