Influences of milling and grinding on machined surface roughness and fatigue behavior of GH4169 superalloy workpieces

Surface topography of superalloy GH4169 workpieces machined by milling and grinding is different significantly. Meanwhile, surface roughness, as one of the main indicators of machined surface integrity, has a great influence on the fatigue behavior of workpieces. Based on analyzing the formation mechanism and characteristics of surface roughness utilizing different machining processes and parameters, the machined surface roughness curve can be decoupled into two parts utilizing frequency spectrum analysis, which are kinematic surface roughness curve and stochastic surface roughness curve. The kinematic surface roughness curve is influenced by machining process,parameters, geometry of the cutting tool or wheel, the maximum height of which is expressed as R'_z.By subtracting the kinematic part from the measurement curve, the stochastic surface roughness curve and its maximum height R'_zcan be obtained, which is influenced by the defects of cutting tool edge or abrasive grains, built-up edges(BUE), cracks, high frequency vibration and so on. On the other hand, the results of decoupling analysis of surface roughness curves indicate that Raand Rz values of milling GH4169 are 2–5 times and 1–3 times as high as those of grinding, while R'_zvalue of milling is 13.85%–37.7% as high as that of grinding. According to the results of fatigue life tests of specimens machined by milling and grinding, it can be concluded that fatigue behavior of GH4169 decreases with the increase of R'_zmonotonically, even utilizing different machining processes.     

Frictional behavior during cold ring compression process of aluminum alloy 5052

The friction is the considerable boundary condition in bulk metal forming. In this paper, the ring compression test was used to evaluate the friction coefficient and factor in Coulomb friction model and Tresca friction model for the plastic deformation of aluminum alloy AA5052. The micro-macro analysis method combining surface morphology and micro-texture was used to explore the friction behaviors in AA5052 cold forming process. In general, the magnitude (μ or m) of friction changes before and after a deformation threshold during ring compression. The maximum change rate of the magnitude (μ or m) before and after the deformation threshold is close to 18.5% under the present experimental conditions, and the change rate decreases with increasing loading speed. The lubrication using MoS₂ is better than that using oil at lower speeds (0.15 mm/s, 1.5 mm/s), but the lubrications for MoS₂ and oil are similar at higher speeds (15 mm/s). The surface roughness, three-dimensional topography, and surface texture of compressed ring have a sudden change around the deformation threshold, which deviate from the previous evolution trend. The increased friction after deformation threshold also promotes the formation of sufficient shear strain layer in the subsurface plane of the compressed ring, and then it hinders the formation of the typical deformation textures with β-oriented line and promotes the appearance of shear textures such as $\left\{\text{001}\right\}〈\text{110}〉$, $\left\{\text{111}\right\}〈\mathit{uvw}〉$ and $\left\{\mathit{hkl}\right\}〈110〉$ textures.     

Time delay compensation in lateral-directional flight control systems at high angles of attack

The previous studies of time delay compensation in flight control systems are all based on the conventional aerodynamic derivative model and conducted in longitudinal motions at low angles of attack. In this investigation, the effects of time delay on the lateral-directional stability augmentation system in high-α regime are discussed based on the $\dot{\beta }$ model, which is proposed in our previous work and proved as a more accurate aerodynamic model to reveal the lateral-directional unsteady aerodynamic characteristics at high angles of attack. Both the $\dot{\beta }$ model and the quasi-steady model are used for simulating the effects of time delay on the flying qualities in high-α maneuvers. The comparison between the simulation results shows that the flying qualities are much more sensitive to the mismatch of feedback gains than the state errors caused by time delay. Then a typical adaptive controller based on the conventional dynamic derivative model and a gain-prediction compensator based on $\dot{\beta }$ model are designed to address the time delay in different maneuvers. The simulation results show that the gain-prediction compensator is much simpler and more efficient at high angles of attack. Finally, the gain-prediction compensator is combined with a linearized $\dot{\beta }$ model reference adaptive controller to compensate the adverse effects of very large time delay, which exhibits excellent performance when addressing the extreme conditions at high angles of attack.     

Intrinsic component filtering for fault diagnosis of rotating machinery

Fault diagnosis of rotating machinery has always drawn wide attention. In this paper, Intrinsic Component Filtering (ICF), which achieves population sparsity and lifetime consistency using two constraints: $l_{1/2}$ norm of column features and $l_{3/2}$ -norm of row features, is proposed for the machinery fault diagnosis. ICF can be used as a feature learning algorithm, and the learned features can be fed into the classification to achieve the automatic fault classification. ICF can also be used as a filter training method to extract and separate weak fault components from the noise signals without any prior experience. Simulated and experimental signals of bearing fault are used to validate the performance of ICF. The results confirm that ICF performs superior in three fault diagnosis fields including intelligent fault diagnosis, weak signature detection and compound fault separation.     

A spanwise loss model for axial compressor stator based on machine learning

In the early stage of aircraft engine design, the through-flow method is an important tool for designers. The accuracy of the through-flow method depends heavily on the accuracy of the loss model. However, most existing models cannot(or cannot well) provide the spanwise loss distribution. To construct an effective spanwise loss model, both turbomachinery knowledge and machine learning skills were used in this paper. A large number of numerical simulations were carried out to build a database con...     

Effect of rotor-mounted protrusion on sealing performance and flow structure in rotor-stator cavity

This paper presents an experimental investigation on the effect of protrusion radial position and height on the sealing performance and flow structure in the rotor-stator cavity. The rotor-mounted protrusions are assembled at three radial positions and are set to three heights. The cavity is equipped with three rim seals: a radial seal, an axial seal and a seal with double fins on the stator. The annulus Reynolds number is set at $4.39\times {10}^5$ and the rotational Reynolds number ranges from $7.51\times {10}^5$ to $1.20\times {10}^6$. Heat and mass transfer analogy is applied. Pressure and ${\mathrm{C}\mathrm{O}}_2$ concentration are measured. The experimental results show that in cavities with different rim seals, radial distributions of the sealing efficiency, pressure and swirl ratio are basically the same. The sealing performance is improved by protrusions compared with the cavity without protrusion and improves with the increase of protrusion radial position and height. The effect of protrusion increases with the increase of the rotational Reynolds number. The windage loss and the flow resistance introduced by protrusions are investigated. It is found that induced windage loss and flow resistance decrease with the increase of protrusion radial position but increase with the protrusion height.     

Validation of the RANS-simulation of laminar separation bubbles on airfoils

This paper presents RANS simulations of the low-Reynolds-number flow past an SD7003 airfoil at $\mathit{Re}=6\times {10}^4$, where transition takes place across a laminar separation bubble. The transition prediction procedure using an approximate envelope method as well as a linear stability solver is discussed. The numerical results are validated against PIV- and force measurements obtained in several wind- and watertunnels and are also compared to XFOIL results. Good agreement is found within the operational range of the airfoil.     

Capturing transition and non-transition flows with a new shear stress transport model

A new Shear Stress Transport(SST) k-ω model is devised to integrate salient features of both the non-transitional SST k-ω model and correlation-based γ-Reθtransition model. An exceptionally simplified approach is applied to extend the New SST(NSST) model capabilities toward transition/non-transition predictions. Bradshaw’s stress-intensity factor ■ can be parameterized with the wall-distance dependent Reynolds number ■; however, as the Reyis replaced by a ‘‘flow-structure-adaptive” parameter Rμ=...     

一种基于动模态分解的翼型流动转捩预测新方法

考虑自由转捩的定常/非定常流动Navier-Stokes方程数值求解,对于翼型流动细节的精确模拟和气动力的精确预测均具有十分重要的意义。采用动模态分解(DMD)方法进行流动稳定性分析,再结合e N方法,提出了一套适用于翼型绕流的转捩预测新方法,称为DMD/e N方法。相比于传统的线性稳定性分析方法,DMD方法不需要求解附面层方程和线性稳定性方程,也没有引入平行流假设,具有更好的理论适用性和算法鲁棒性。开展了NLF0416、S809和SD7003等翼型的转捩预测数值验证研究,通过与实验结果以及与传统的基于线性稳定性分析的e N方法的比较,验证了本文所发展的转捩预测新方法在预测翼型的定常流动和非定常流动转捩方面的正确性,也表明了该方法具有解决含层流分离泡的翼型绕流转捩预测的能力。     

Artificial equilibrium points and bi-impulsive maneuvers to observe 243 Ida

In the restricted three-body problem, the traditional Lagrange points L₁ and L₂ are the only equilibrium points near the asteroid 243 Ida. The thrust generated by a solar sail over a spacecraft enables the existence of new artificial equilibrium points, which depend on the position of the spacecraft with respect to the asteroid and the attitude of the solar sail. Such equilibrium points generate new spots to observe the body from above or below the plane of motion. Such points are very good observational locations due to their stationary condition. This work provides a preliminary analysis to observe Ida through the use of artificial equilibrium points as spots combined with transfer maneuvers between them. Such combination can be used to observe the asteroid from more different points of view in comparison to fixed ones. The analyses are made for a spacecraft equipped with a solar sail and capable of performing bi-impulsive maneuvers. The solar radiation pressure is used both to maintain the equilibrium condition and to reduce the costs of the transfers and/or to create transfers with longer duration. This is a new aspect of the present research, because it combines the continuous thrust with initial and final small impulses, which are feasible for most of the spacecraft, because the magnitudes of the impulses are very low. These combined maneuvers may reduce the transfer times of the maneuvers in most of the cases, compared with the maneuvers based only on continuous thrust. Several options involved in these transfers are shown, like to minimize the fuel spent ($\mathrm{\Delta }\mathit{v}$) as a function of the transfer time or to extend the duration of the travel between the points. Extended transfer times can be useful when observations are required during the transfers.