Propulsion and Power Research最新文献

For advanced aero-engine design and research, modeling and simulation in a digital environment is indispensable, especially for engines of complicated configurations, such as variable cycle engines (VCE) and adaptive cycle engines (ACE). Also, in the research of future smart engines, reliable real-time digital twins are paramount. However, the 2 dominant methods that used in solving the simulation models, Newton-Raphson (N-R) method and volume-based method, are not fully qualified for the study requirements, because neither of them reaches the satisfactory balance of convergence rate and calculating efficiency. In this study, by deeply analyzing the mathematical principle of these 2 methods, a novel modeling and solving method for aero-engine simulation, which integrates the advantages of both N-R and volume-based methods, is established. It has distributed architecture and local quadratic convergence rate. And a novel modeling method for variable area bypass injectors (VABI) is put forward. These facilitate simulation of various configurations of aero-engines. The modeling cases, including a high bypass-ratio (BPR) turbofan and an ACE, illustrate that the novel technique decreases the iterations by about two-thirds comparing with volume-based method, while the success rate of convergence remains over 99%. This proves its superiority in both convergence and calculating efficiency over the conventional ones. This technique can be used in advanced gas turbine engine design and control strategy optimization, and study of digital twins.

The interaction of cowl shock wave and boundary layer has a crucial effect on the stability, operability and performance of hypersonic inlets. Many studies on inhibiting the separation and managing the strength of the interaction of the shock wave and boundary layer with expansion corner have been conducted. However, the expansion waves near the circular arc shoulder to effectively control the interaction and cowl shock arrangement is little investigated. Therefore, the interaction of the cowl shock wave and boundary layer under the fluence of the expansion waves is studied by inviscid and viscous numerical simulations. The results reveal that the expansion waves have an important impact on the interaction between the cowl shock wave and boundary layer and the strength of shock wave, and that there are four types of interaction processes with the change of the relative impingement positions of cowl shock wave. The expansion waves have a different influence on the shock wave and boundary layer interaction at different incident points. When the incident point of the cowl shock wave goes far downstream from the end of the circular arc shoulder, the influence of expansion waves is weakened, and the magnitude of separation zone increases. However, when the expansion waves are applied to the interaction of the cowl shock wave and boundary layer on the circular arc shoulder, the separation can be effectively controlled. In particular, while the expansion waves interact with the shock wave and boundary layer in the back half of the circular arc shoulder, the separation is best inhibited. Compared with the upstream and downstream incident points, the scale of separation area in the optimal control region is reduced by 65.3% at most. Furthermore, the total pressure recovery coefficient first increases and then decreases when the cowl moves from upstream to downstream, and the total pressure recovery coefficient reaches the maximum value of 68.36% at the incident position of cowl shock wave d = 8.09δ₀.

In this study, we have analyzed fluid mobility and thermal transport of the SiO₂/kerosene nanofluid within two rotating stretchable disks. The top disk is simulated to be oscillating with a periodic velocity and squeezing continuously the nanofluid within a porous medium and making the fluid to flow perpendicularly to the situated magnetic field. Thermal radiation effects are considered in the heat transfer model. The non-linear (NL) PDEs that describe the nanofluid mobility structure and thermal transport are transformed into system of NL-ODEs by introducing adequately suitable non-dimensional variables after which the NL-ODEs were numerically solved via spectral quasi-linearization method (SQLM) on overlapping grids. The consequences of several pertinent parameters of the model on pressure, temperature, velocity, skin drag coefficient and thermal transport rate are examined and elucidated in detail with the aid of figures and tables. It was found that the flow structure with prescribing conditions develops negative pressure situation which has vast applications in modern day medical engineering, especially in the construction of air pressure stabilizers used in medical isolation and wound therapy physiology.

As the transport sector is responsible for the consumption of a vast proportion of the oil produced, it is mandatory to research feasible solutions to tackle this issue. The application of aerodynamic attachments for passive flow control and reducing resisting aerodynamic forces such as drag and lift is one of the most practicable ways to minimize vehicle energy consumption. The flaps are one of the most innovative aerodynamic attachments that can enhance the flow motion in the boundary layer at the trailing edge of the wings. In the present paper, the flap is designed and modeled for controlling the airflow at the roof-end of a 2D Ahmed body model, inspired by the schematic of the flap at the trailing edge of the wing. As a result, the flap's geometry and position from the roof-end of the car model are parameterized, which leads to having four design variables. The objective functions of the present study are the vehicle's drag coefficient and lift coefficient. 25 Design of Experiment (DOE) points are considered enabling the Box-Behnken method. Then, each DOE point is modeled in the computational domain, and the flow-field around the model is simulated using Ansys Fluent software. The results obtained for the DOE points are employed by different regressors, and the relation between design variables and objective functions is extracted using GMDH-ANN. The GMDH-ANN is then coupled with three types of optimization algorithms, among which the Genetic algorithm proves to have the most ideal coupling process for optimization. Finally, after analyzing the variations in the geometry and position of the roof flap from the car roof-end, the roof-flap with specifications of L = 0.1726 m, α = 5.0875°, H = 0.0188 m, and d = 0.241 m can optimize the car drag and lift coefficients by 21.27% and 19.91%, respectively. The present research discusses the opportunities and challenges of optimal design roof-flap geometry and its influence on car aerodynamic performance.

The present study investigates the axisymmetric stagnation point radiative flow of a Cu-Al₂O₃/water hybrid nanofluid over a radially stretched/shrunk disk. In this paper, a new mathematical model has been developed by taking into consideration the concept of different nanoparticles concentration in a hybrid nanofluid, which are Brownian motion and thermophoresis of nanoparticles. A new model for entropy generation has also been provided in the present study. The non-dimensional governing equations of the developed mathematical model are solved using newly developed and efficient overlapping grid spectral collocation method. Numerical stability and residual error test are provided here to show the accuracy of the numerical method in this mathematical model. The outcomes of fluid flow, temperature, and two different types of concentration profiles are depicted, and described in graphical and tabular forms. For the limiting instances, comparison shows excellent agreement among current and results established in the literature. Increasing the strength of magnetic field is seen to increase the radial component of fluid velocity as well as the entropy generated within the system. Two different nanofluid concentration profiles are increasing and decreasing with rising thermophoresis and Brownian motion parameters, respectively, from a particular height above the disk because of the revised nanofluid boundary condition. Temperature profile increases here with increasing Biot number, and increasing Brinkman number causes higher entropy generation number for both stretching and shrinking disks. The enhanced thermal characteristics of the hybrid nanofluid over the single particle nanofluid has been observed.

Variable cycle engine (VCE) is one of the most promising technologies for the next-generation aircraft, the matching of different components in the compression system is a key difficulty VCE faced. To investigate the component matching mechanisms in the VCE compression system, an advanced throughflow program is employed to calculate the characteristic lines of each component, and a zero-dimensional method is developed to capture the component performance deviation during the coupling working process. By setting the compressor stall and choke conditions as the boundary, the operation range of the compression system is first clarified, and the aerodynamic performance in the operation zone is discussed, thus providing a theoretical basis for optimization of the engine operating control scheme. Results show that the efficiency of the core flow is optimum at the left-bottom corner of the operation region, while the total pressure ratio peaks at the right-top area, hence a balance is needed when deciding the matching point. Regulations of component control parameters will change the position of the operation zone, as well as the corresponding aerodynamic performance. Decreasing the core driven fan stage rotating speed can improve the total bypass ratio, yet the total pressure ratio of the core flow will be decreased. Closing the core driven fan stage inlet guide vane can increase the total bypass ratio without changing the core flow aerodynamic performance significantly. The bypass ratio of the compression system can also be increased by increasing the fan stall margin or decreasing its rotating speed, both ways will decrease the total pressure ratio of the core flow. Results of the study will benefit the variable cycle engine design process in operation point evaluation and thermodynamic cycle optimization.