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The circumferentially averaged equation of the inlet flow radial equilibrium in axial compressor was deduced. It indicates that the blade inlet radial pressure gradient is closely related to the radial component of the circumferential fluctuation (CF) source item. Several simplified cascades with/without aerodynamic loading were numerically studied...
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... requiring the evaluation of the primitive variables and the first derivatives of them at the middle of the cell edge. An explicit Runge-Kutta method was employed for the time discretization as it is straightforward to implement. The 2D meshes were created using bilinear interpolation method and the grid was densified near the LE, as shown in Fig. 4. The details of the circumferentially averaged method can be found in Ref. ...
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... In present study, a well-developed CDA, called MAN GHH 1-S1 (Steinert et al. 1991), is employed to be the basic research airfoil (for convenience, present study abbreviates this airfoil to MAN airfoil hereafter). This airfoil has well-documented performance data of design and off-design conditions and has been widely used in compressor blade research Chang et al. 2015;Xu et al. 2017). The cascade parameters are shown in Fig. 5 and the profile coordinate data can be found in Steinert et al. (1991). ...
To improve the optimization accuracy and efficiency, state variable and optimization potential-based multi-objective optimization (MOP) method is introduced. State variable records whether the simulation failed, which caused by ill geometry and mismatched predetermined boundary condition, and is consequently incorporated into objective function through weighted average method to improve the accuracy of surrogate model and optimization. Optimization potential, which represents the difference between present performance and ideal optimal objective, can be used to direct MOP and avoids the manual selection of weight vectors. Four optimization cases, including traditional weighted optimization, state variable based optimization, optimization potential based optimization, and the optimization combined presented two methods, are applied to optimize a typical compressor blade airfoil and demonstrate the proposed optimization method. Results show that the combination of these two methods produces the best optimization result. In which the state variable method generates most of improvement in optimal performance and the optimization potential method notably improves optimal performance under large incidences. The introduction of state variable excludes the invalid objective values at one sample point rather than directly removing or keeping, so that the accuracy of surrogate model is significantly improved and obtains better optimal results. The distribution of optimization potential among each incidence is similar to that of weight vector. Using its summation to construct objective function can be deemed as automatically assigning a preferable weight vector and the optimal result consequently presents slight preferable performance.
... Due to considerable potential uses in a number of areas, such as flow separation control, boundary layer transition, mixing enhancement, drag and noise reduction, etc. [1][2][3][4][5] , Active Flow Control (AFC) methods have been one of the hotspots in fluid mechanics. Plasma actuators are an attractive type of active flow control technique [6][7][8][9] . ...
Plasma Synthetic Jet (PSJ) actuators have shown wide and promising application prospects in high-speed flow control, due to their advantages including high exhaust speed, wide frequency band, rapid response, and non-moving components. Although previous studies on PSJ actuators are abundant, most of them have focused on the performance of a single actuator. However, in practice, an actuator array is very necessary for large-scale aerodynamic actuation on account of the small affected area of a single PSJ. In this paper, the characteristics of a two-electrode plasma synthetic jet actuator array in serial are investigated experimentally. Compared to a parallel actuator array, the serial actuator array requires simpler power supply design and is much easier to realize. High-speed photography of the discharge evolution, voltage-current measurement, and shadowgraphy visualization are used in the investigation. Experimental results show that, for the serial actuator array, weak discharges happen firstly between energized and suspending electrodes, and then a strong pulse arc discharge is triggered. The breakdown voltage in serial is irrelevant to such factors as the number of actuators, the maximum or minimum gap in serial, the connection sequence, etc. It is mainly determined by the sum of gaps. For serial actuators with the same anode-to-cathode spacing, the energy deposition is the same, and the jet is synchronous and similar. Because of the entrainment and merging of adjacent jet vortices, the jet front speed of an aligned synchronous jet array increases as the orifice distance decreases. To achieve the highest jet front velocity, the orifice of the actuator has an optimal diameter.
Current research on engine transient performance primarily focuses on the variation of key aerothermodynamic parameters in specific sections, neglecting the comprehensive understanding of the engine's inner flow field during transient operations. To address this gap, this paper proposes a 2D transient simulation method that effectively captures the evolution of the flow field in the meridional plane. The approach involves deriving circumferential averaging equations in a rotating coordinate system with variable angular velocity, considering angular acceleration source terms. The engine components, including the compressor, combustion chamber, turbine, and rotating shaft, are individually modeled. The newly derived governing equations are solved using a dual-time step approach, where an inner-iteration ensures mass flow conservation, and an outer-iteration updates the rotational speed. Using a real turbojet engine as a case study, transient examinations comprising acceleration and deceleration are performed. A comparative analysis of experimental and simulation results is conducted, revealing an average error of 0.9% in shaft speed, 7.8% in engine thrust, 1.7% in engine exhaust temperature, and 5.1% in compressor outlet pressure. Additionally, the study analyzes and compares the internal flow fields during the transient process, contributing to a deeper understanding of the engine's dynamic behavior. The research effort establishes a practical methodology and technology for conducting comprehensive two-dimensional engine transient cycle analyses within reasonable computational resources and timeframes.
In the current state-of-the-art, high-loss flow in the endwall significantly influences compressor performance. Therefore, the control of endwall corner separation in compressor blade rows is important to consider. Based on the previous research of the Blended Blade and EndWall (BBEW) technique, which can significantly reduce corner separation, in combination with a non-axisymmetric endwall, the full-BBEW technique is proposed in this study to further reduce the separation in endwall region. The principle of the unchanged axial passage area is considered to derive the geometric method for this technique. Three models are further classified based on different geometric characteristics of this technique: the BBEW model, Inclining-Only EndWall (IOEW) model, and full-BBEW model. The most effective design of each model is then found by performing several optimizations at the design point and related numerical investigations over the entire operational conditions. Compared with the prototype, the total pressure loss coefficient decreases by 7%–9% in the optimized full-BBEW at the design point. Moreover, the aerodynamic blockage coefficient over the entire operational range decreases more than the other models, which shows its positive effect for diffusion. This approach has a larger decrease at negative incidence angles where the intersection of the boundary layer plays an important role in corner separation. The analysis shows that the blended blade profile enlarges the dihedral angle and creates a span-wise pressure gradient to move low momentum fluid towards the mainstream. Furthermore, the inclining hub geometry accelerates the accumulated flow in the corner downstream by increasing the pressure gradient. Overall, though losses in the mainstream grow, especially for large incidences, the full-BBEW technique effectively reduces the separation in corners.
