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In response to the problem of poor lubrication effect and unstable bearing operation leading to bearing failure in traditional bearings, the solution of installing a jet device on the bearing has been proposed. Using numerical calculation software, analyze the impact of installing a semi-circular or 1/4 circular jet device on the temperature field and leakage rate of the bearing. The results show that after installing a jet control device, the temperature of the flow field around the bearing decreases significantly at the same inlet pressure, while the leakage rate decreases. Keeping the speed and oil temperature constant, as the pressure at the lubricating oil inlet increases, the leakage rate decreases by 51.87% -59.80%; Keeping the rotational speed and oil inlet pressure unchanged, as the temperature of the lubricating oil at the inlet increases, the leakage decreases by 45.94% -50.74%; Keeping the inlet pressure and oil temperature unchanged, when the speed increases, the leakage decreases by 12.58% -18.31%. Install a jet device on the end face of the bearing to achieve collaborative design of low leakage and low temperature rise at the bearing, thus providing a theoretical basis for the long-term design of the bearing.

Gas turbine is a promising device for power generation and propulsion either using traditional or renewable energy fuels. One of its key problems is the flow instability of compressors especially with the increase in blade load and changeable working environment. To intelligently and efficiently inhibit flow separation and enhance the pressure rise ability of highly loaded compressors under variable operating conditions, a novel flow control technique termed as adaptive Coanda jet control (ACJC) is proposed in this paper for a compressor stator cascade with a high diffusion factor of 0.66. To realize the ACJC strategy, an incidence angle (IA) prediction model and an optimal injection mass flow rate (OIMFR) prediction model are established by adopting single factor analysis of variance, principal component analysis and Back Propagation Neural Network (BPNN) methods. Two inlet Mach numbers including 0.1 and 0.4 are considered to represent incompressible and compressible flow conditions, and different inlet incidence angles are involved to model various off-design working situations of the real compressor. Effectiveness of the ACJC system is evaluated using numerical simulations are performed to understand the effects of the injection mass flow ratio on the flow field and aerodynamic performance of the blade cascade. Results indicate that the ACJC system can accurately predict the optimal injection mass flow ratio that can achieve the minimum flow loss at each incidence angle. Compared to the cascade without ACJC under the incidence angel of 5°, the optimal injection mass flow ratio being 1.27% and 1.20% can reduce the total pressure loss coefficient by 18.88% and 21.56% for incoming Mach number being 0.1 and 0.4, respectively.

In this paper, computational fluid dynamic (CFD) analysis and experiments have been carried out to study the effect of nozzle pressure ratio, i.e. the ratio of inlet pressure to atmospheric pressure, and the pitch circle diameter of the control jets to regulate the base pressure. The variables considered for the analysis as well as the experiments are the nozzle pressure ratio (NPR), the Mach number (M) and the pitch circle diameter (PCD) of the control jets. The area ratio considered for the study is kept constant at 4.84 while the length to diameter (L/D) ratio of an enlarged duct is set constant at 5. The inertia parameter considered for the study is Mach number. The Mach numbers considered for study are 1.5, 2.0, and 2.5. The nozzle pressure ratio considered for study are 2, 5 and 8. Three different pitch circle diameters of control jets considered for study are 13.1 mm, 16.2 mm and 19.3 mm. From the numerical simulations and the results of the experimental tests, it is found that the control jets are very beneficial to increase the base pressure at higher NPR when the jets issuing from the nozzles are under-expanded. The control jets were able to increase the base pressure value from 160% to 400% at nozzle pressure ratio 8. It is concluded that the parameter D3 is the most effective pitch circle diameter of the control jets to increase the base pressure.

At present, there is no publicly published research on the unsteady interference effect in the start-up process of the lateral jet control of the spinning missile. The variation of aerodynamic characteristics during the jet start-up process of the spinning missile is still unclear. Therefore, the unsteady numerical method based on the three-dimensional unsteady compressible Navier–Stokes equations and the sliding mesh method is used to study the unsteady jet interference characteristics of the spinning missile during the starting process of the lateral jet. Based on the verification of the numerical simulation method in this paper, the jet interference flow field under the conditions of non-rotation and rotation is simulated, and the variation of the aerodynamic characteristics of the missile under the two conditions is given. The influence of rotation on the unsteady aerodynamic characteristics of the lateral-jet-controlled spinning missile is analyzed. The flow mechanism resulting in the change of the jet control characteristics and the lateral aerodynamic characteristics of the missile is analyzed through the interference flow field structure at different moments after the jet starts. The results indicate that in the start-up process of pulse jet control, the jet interference characteristics on the fins have a delay effect compared with the projectile body. The duration of the unsteady effect caused by the high-pressure region upstream of the nozzle is shorter than that caused by the low-pressure region downstream of the nozzle. The flow separation and reattachment near the nozzle have strong unsteady characteristics. The jet wake has the most obvious interference effect on Fin1. The pressure on the side of the rotation direction of Fin1 increases, while the opposite side is in contrast.

A data-driven framework using snapshots of an uncontrolled flow is proposed to identify, and subsequently demonstrate, effective control strategies for different objectives in supersonic impinging jets. The open-loop, feed-forward control approach, based on a dynamic mode decomposition reduced-order model (DMD-ROM), computes forcing receptivity in an economical manner by projecting flow and actuator-specific forcing snapshots onto a reduced subspace and then evolving the dynamics forwards in time. Since it effectively determines a linear response around the unsteady flow in the time domain, the method differs materially from typical techniques that use steady basic states, such as stability or input–output approaches that employ linearized Navier–Stokes operators in the frequency domain. The method presented naturally accounts for factors inherent to the snapshot basis, including configuration complexity and flow parameters such as Reynolds number. Furthermore, gain metrics calculated in the reduced subspace facilitate rapid assessments of flow sensitivities to a wide range of forcing parameters, from which optimal actuator inputs may be selected and results confirmed in scale-resolved simulations or experiments. The DMD-ROM approach is demonstrated from two different perspectives. The first concerns asymptotic feedback resonance, where the effects of harmonic pressure forcing are estimated and verified with nonlinear simulations using a blowing–suction actuator. The second examines time-local behaviour within critical feedback events, where the phase of actuation becomes important. For this, a conditional space–time mode is used to identify the optimal forcing phase that minimizes convective instability growth within the resonance cycle.

In response to the need to enhance the aerodynamic characteristics of a bi-directional flying wing with bilateral symmetric airfoil during the takeoff and landing phases, this study investigates the effects of variable camber technology combined with active flow control using blow-jet on such symmetric airfoils. A Computational Fluid Dynamics (CFD) method was developed for this research. The study examines the effects of jet intensity on the aerodynamic performance and flow field characteristics, as well as the underlying mechanisms of these bilateral symmetric airfoils. The results demonstrate that blow-jet control increases circulation and maintains attached flow on the airfoil surface by elevating the fluid velocity over the airfoil. This effectively suppresses flow separation, enhances lift, reduces drag, and improves the lift-to-drag ratio, thereby significantly improving the aerodynamic performance of the symmetric airfoils. As the jet intensity parameter C μ-j increases, the lift coefficient rises, the drag coefficient decreases, and the power consumption coefficient increases, while the Equivalent lift-to-drag ratio initially increases and subsequently decreases. The findings of this study provide valuable insights for improving the short-distance takeoff and landing performance of bi-directional flying wing aircraft.

This article discusses the research progress of flow control technology in reducing road vehicle drag in the context of energy scarcity and climate crisis. Flow control can effectively reduce the aerodynamic resistance encountered by vehicles during operation, providing new solutions for improving vehicle power and fuel efficiency. This review provides an overview of the literature on how flow control changes the aerodynamic characteristics of road vehicles (such as squareback, fastback, and notchback). Firstly, this article compares the drag reduction effects of different flow control devices installed at different vehicle positions. Among them, active flow control and synthetic jet control of ordinary blowing/suction flow can usually reduce the resistance of road vehicles by about 10%, while micro-jet and plasma jets can only show significant drag reduction characteristics under high-speed conditions. Passive flow control devices such as deflectors, tail fins, and vortex generators can achieve a maximum drag reduction rate of nearly 30%, or increase lift at the cost of increasing some drag. Combination flow control can achieve higher drag reduction effects than a single control method. Secondly, this article provides an overview of the integration of closed-loop control and flow control, and delves into how advances in computing power and machine reinforcement learning will greatly enhance the future achievements of road vehicle drag reduction research. Finally, the development prospects and future directions of different types of flow control technologies were discussed.

The jet can be applied to the yaw control of a projectile, however, the complex interaction of the jet with the supersonic mainstream makes the flow field complex and yaw force unpredictable. To reveal the evolution of flow structures under different pressure ratios (PRs), or momentum flux ratios, a transverse sonic jet injected into a supersonic laminar crossflow has been studied numerically. Large-eddy simulations are employed to simulate the flow fields and evolution tendency of flow structures under different PRs of 10, 50, 100, 300, and 500. Our results show clearly the shock and flow structures of the jet interaction with crossflow under different PRs. Moreover, we find that, with the increase of PR, a larger upstream recirculation zone (RZ) and jet shock core appear, which accelerates the transformation of the bow shock (BoS) and the instability of the jet shear layer due to its stronger interaction with the crossflow. In addition, a high PR also accelerates RZ instability and produces a strong compressing effect on the major counter-rotating vortex pair in the jet flow, which makes the streamwise vortex tube stronger in the wake. These findings provide important information for applications of jet control of projectiles.

A parametric study is conducted for the control of a turbulent jet using a single unsteady minijet. A number of control parameters that influence the decay rate $K$ of the jet centreline mean velocity are investigated, including the mass flow rate ratio $C_{m}$ , excitation frequency ratio $f_{e}/f_{0}$ and exit diameter ratio $d/D$ of the minijet to main jet, along with the duty cycle ( $\\unicode[STIX]{x1D6FC}$ ) of the minijet injection. Extensive hot-wire, particle image velocimetry and flow visualization measurements were performed in the manipulated jet. Various flow structures have been identified, such as the flapping flow, non-flapping flow and that showing a manipulable thrust vector, depending on $C_{m}$ , $f_{e}/f_{0}$ and $\\unicode[STIX]{x1D6FC}$ . Empirical scaling analysis unveils that, prior to the minijet impingement upon the wall of the nozzle and the generation of turbulence, the relationship $K=g_{1}$ ( $C_{m}$ , $f_{e}/f_{0}$ , $d/D$ , $\\unicode[STIX]{x1D6FC}$ ) may be reduced to $K=g_{2}$ ( $\\unicode[STIX]{x1D709}$ ), where $g_{1}$ and $g_{2}$ are different functions and the scaling factor $\\unicode[STIX]{x1D709}=(\\sqrt{MR}/\\unicode[STIX]{x1D6FC})(d/D)^{n}$ ( $\\sqrt{MR}\\equiv C_{m}(D/d)$ is the momentum ratio and $n$ is a constant that depends on $\\unicode[STIX]{x1D6FC}$ ) is physically the effective momentum ratio per pulse or effective penetration depth. Discussion is conducted based on $K=g_{2}$ ( $\\unicode[STIX]{x1D709}$ ), which provides important insight into the jet control physics.

With the capability of high speed flying, a more reliable and cost efficient way to access space is provided by hypersonic flight vehicles. Controller design, as key technology to make hypersonic flight feasible and efficient, has numerous challenges stemming from large flight envelope with extreme range of operation conditions, strong interactions between elastic airframe, the propulsion system and the structural dynamics. This paper briefly presents several commonly studied hypersonic flight dynamics such as winged-cone model, truth model, curve-fitted model, control oriented model and re-entry motion. In view of different schemes such as linearizing at the trim state, input-output linearization, characteristic modeling, and back-stepping, the recent research on hypersonic flight control is reviewed and the comparison is presented. To show the challenges for hypersonic flight control, some specific characteristics of hypersonic flight are discussed and the potential future research is addressed with dealing with actuator dynamics, aerodynamic/reaction-jet control, flexible effects, non-minimum phase problem and dynamics interaction.