The rapid development of high-speed railways necessitates the development of new materials for switch slide baseplates. In this study, a Cu–Ni–graphite composite, containing 1 wt% to 6 wt% graphite and prepared by powder metallurgy, was used as a potential material. Pin-on-disk wear tests were conducted to measure the sliding friction of the Cu–Ni–graphite composite against U75 V steel. The results showed that the friction coefficients gradually decreased when the graphite content in the composite ranged from 1 wt% to 4 wt% in the composite. When the graphite content was 4 wt%, the friction coefficient reached the minimum value (0.153). When the graphite content was low (1 wt% to 4 wt%), the primary wear mechanism was microcutting. An increased graphite content facilitated the generation of lubricating films and decreased the wear damage. As the graphite content increased from 4 wt% to 6 wt%, the friction coefficients also increased. The variation in the wear volume rate had the same tendency as the friction coefficient. When the graphite content exceeded 4 wt%, the primary wear mechanism was delamination and fatigue wear. Due to the tendency to form cracks on the subsurface and the plentiful generation of the spalled pits, the graphite fragments could not completely form lubricating films but separated as wear debris. The lubricating films existing on the U75 V steel were in proportion to the graphite content in the composite. The wear weight loss of the U75 V steel exhibited a reduction with increasing graphite content.

Phase separation has been proven to be beneficial to air-cooled parallel flow microchannel condensers for air conditioning systems. The inlet to the condenser with phase separation is at the middle of the condenser height. After the first pass, in the vertical second header of the condenser, refrigerant vapor separates from liquid mainly due to gravitational effects. In ideal case, vapor should go to the top exit and liquid to the bottom exit, resulting in increased heat transfer. Due to interaction between vapor and liquid, separation is not perfect, expressed through the separation efficiency. This paper presents a parametric study of phase separation efficiency in the intermediate headers, with the target to improve separation efficiency. Header prototypes which have two exits are made with transparent polyvinyl chloride (PVC) to simulate the real header and provide visual access. Using R-134a as a baseline, the measurement of separation efficiency and its general trend will be shown first. The experimental results are compared to the simulation of a mechanistic model based on flow regime and force balance analysis. Inlet mass flux in simulation is controlled at 87–311 kg · m −2 · s −1 and inlet quality at 0.05–0.25. The observed flow patterns in header are compared with the modeling results. Then, the header diameter is increased, which effectively improves the separation efficiency due to reduction of vapor velocity in header. Finally, R245fa and R32 are modeled in comparison with R-134a to discuss the effect of fluid properties on separation efficiency.

Phase separation has been proven to increase performance of condensers of energy conversion systems (in vapor compression systems). Instead of conventional design, the inlet to a microchannel condenser prototype is in the middle of the height. After the first pass, in the vertical second header of the condenser, vapor phase separates from liquid phase due to gravity, and sometimes other effects. In ideal case vapor should go to the top and liquid to the bottom, resulting in increased heat transfer. Due to interaction between vapor and liquid, separation is not perfect, expressed through the separation efficiency. A mechanistic model presented in the paper is built to predict the phase separation efficiency based on force balance analysis for the liquid phase and correlations for the two-phase pressure drop. For the force balance criteria, liquid phase is divided into droplets and film and treated separately. Initial agreement with experiment is achieved to be within ±15%. For a second header at one inlet condition of the flow, the liquid separation efficiency is a function of the vapor separation efficiency. Liquid separation efficiency decreases with increasing inlet mass flux.

Systems with hidden attractors have been the hot research topic of recent years because of their striking features. Fractional-order systems with hidden attractors are newly introduced and barely investigated. In this paper, a new 4D fractional-order chaotic system with hidden attractors is proposed. The abundant and complex hidden dynamical behaviors are studied by nonlinear theory, numerical simulation, and circuit realization. As the main mode of electrical behavior in many neuroendocrine cells, bursting oscillations (BOs) exist in this system. This complicated phenomenon is seldom found in the chaotic systems, especially in the fractional-order chaotic systems without equilibrium points. With the view of practical application, the spectral entropy (SE) algorithm is chosen to estimate the complexity of this fractional-order system for selecting more appropriate parameters. Interestingly, there is a state variable correlated with offset boosting that can adjust the amplitude of the variable conveniently. In addition, the circuit of this fractional-order chaotic system is designed and verified by analog as well as hardware circuit. All the results are very consistent with those of numerical simulation.

This paper presents a numerical investigation on the sealing effectiveness and unsteady flow field of a 1.5-stage turbine with the front and aft wheel-space cavities. The sealing effectiveness and flow structure are studied by solving three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) equations and shear stress transfer (SST) turbulence model. The numerical pressure and swirl ratio distributions in cavities with two computational models are compared with experimental data to determine the position of stationary/rotating domain interface. The time-averaged mainstream pressure distribution and sealing effectiveness of the rim seal at the front and aft cavities are studied by the steady and unsteady calculations. The unsteady results agree well with experimental data by comparison of the steady calculations. The effects of coolant flow rates on the sealing effectiveness and the flow field of the rim seal at the front and aft cavities are investigated. The obtained results show that the sealing effectiveness of the rim seal at the aft cavity is much larger than that of the rim seal at the front cavity at the same coolant flow rate. The less mainstream pressure fluctuation near the aft rim seal clearance and the clockwise vortex due to the pumping effect in the aft rim seal leads to this result. The mainstream pressure fluctuation downstream of the blade and the sealing effectiveness of the rim seal at the aft cavity under five operating conditions are computed. It shows that the square root of the mainstream pressure fluctuation amplitude downstream of the blade is proportional to the mainstream flow rate. The increase of the mainstream flow results in gradual decrease of the sealing effectiveness of the rim seal at the aft cavity.

In order to further study the effects of the target channel shape on the cooling performance of the double swirl cooling (DSC), five double swirl channels formed by two overlapping elliptic cylinders with different length ratio between the vertical semi-axis and the horizontal semi-axis are applied. Numerical studies are carried out under three Reynolds numbers. The flow characteristics and heat transfer performance of five DSC cases are compared with the benchmark impingement cooling case. The flow losses, cross-flow development, generated vortices, and velocity distributions inside target channels are illustrated, analyzed, and compared. The spanwise averaged Nusselt number, Nusselt number distributions, and thermal performance are discussed and compared. Results indicate that the largest length ratio between the vertical semi-axis and the horizontal semi-axis of the target channel yields the lowest flow loss, largest overall averaged Nusselt number, and best thermal performance. With the decrease in the length ratio, the heat transfer distribution on the target surface becomes more uniform. The maximum enhancement of overall averaged Nusselt number and thermal performance in DSC is about 30% and 33%, respectively.

This paper presents a detailed experimental and numerical study on the effects of upstream step geometry on the endwall secondary flow and heat transfer in a transonic linear turbine vane passage with axisymmetric converging endwalls. The upstream step geometry represents the misalignment between the combustor exit and the nozzle guide vane endwall. The experimental measurements were performed in a blowdown wind tunnel with an exit Mach number of 0.85 and an exit Re of 1.5 × 10 6 . A high freestream turbulence level of 16% was set at the inlet, which represents the typical turbulence conditions in a gas turbine engine. Two upstream step geometries were tested for the same vane profile: a baseline configuration with a gap located 0.88C x (43.8 mm) upstream of the vane leading edge (upstream step height = 0 mm) and a misaligned configuration with a backward-facing step located just before the gap at 0.88C x (43.8 mm) upstream of the vane leading edge (step height = 4.45% span). The endwall temperature history was measured using transient infrared thermography, from which the endwall thermal load distribution, namely, Nusselt number, was derived. This paper also presents a comparison with computational fluid dynamics (CFD) predictions performed by solving the steady-state Reynolds-averaged Navier–Stokes with Reynolds stress model using the commercial CFD solver ansys fluent v.15. The CFD simulations were conducted at a range of different upstream step geometries: three forward-facing (upstream step geometries with step heights from −5.25% to 0% span), and five backward-facing, upstream step geometries (step heights from 0% to 6.56% span). These CFD results were used to highlight the link between heat transfer patterns and the secondary flow structures and explain the effects of upstream step geometry. Experimental and numerical results indicate that the backward-facing upstream step geometry will significantly enlarge the high thermal load region and result in an obvious increase (up to 140%) in the heat transfer coefficient (HTC) level, especially for arched regions around the vane leading edge. However, the forward-facing upstream geometry will modestly shrink the high thermal load region and reduce the HTC (by ∼10% to 40% decrease), especially for the suction side regions near the vane leading edge. The aerodynamic loss appears to have a slight increase (0.3–1.3%) because of the forward-facing upstream step geometry but is slightly reduced (by 0.1–0.3%) by the presence of the backward upstream step geometry.

The modern compressor operation is challenged by the liquid presence in wet gas operating conditions. The liquid phase may affect the compressor stability by partially flooding the internal annular gas seals and inducing subsynchronous vibration (SSV). To improve the annular seal behavior and increase the rotor stability, high-precision results of leakage flow rates and rotordynamic force coefficients are needed for annular gas seals in wet gas conditions. In order to better understand the leakage and rotordynamic characteristics of the annular gas seal in wet gas conditions, a 3D transient CFD-based perturbation method was proposed for computations of leakage flow rates and rotordynamic force coefficients of annular gas seals with liquid phase in main gas phase, based on inhomogeneous Eulerian-Eulerian multiphase flow model, mesh deformation technique, and the multifrequency rotor whirling orbit model. Numerical results of frequency-dependent rotordynamic force coefficients and leakage flow rates were presented and compared for three types of noncontact annular gas seals, which include a smooth plain annular seal (SPAS), a labyrinth (LABY) seal, and a fully partitioned pocket damper seal (FPDS). These three seals were designed to have the identical rotor diameter, sealing clearance, and axial length. The accuracy and the availability of the present transient CFD numerical method were demonstrated with the experiment data of leakage flow rates and frequency-dependent rotordynamic force coefficients of the smooth plain seal with four inlet liquid volume fractions (LVFs) of 0%, 2%, 5%, and 8%. Steady and transient numerical simulations were conducted at inlet air pressure of 62.1 bar, pressure ratio of 0.5, rotational speed of 15,000 rpm, and inlet preswirl ratio of 0.3 for four inlet LVFs varying from 0% to 8% and 14 subsynchronous and synchronous whirling frequencies up to 280 Hz. The numerical results show that the inlet liquid phase has a significant influence on the leakage and rotordynamic coefficients for all three types of annular gas seals. The mixture leakage flow rate increases with the increasing inlet LVF, combining the decreasing gas-phase and linearly increasing liquid-phase leakage flow rates. The smooth plain seal leaks the most gas phase and liquid phase, followed by the pocket damper seal (PDS) and then the labyrinth seal. Increasing inlet LVF significantly decreases the direct stiffness and slightly increases the effective damping of the smooth plain seal. The labyrinth seal possesses evident negative direct stiffness and shows a noticeable decreasing effective damping with the increasing inlet LVF at the subsynchronous frequency range. Increasing inlet LVF obviously increases all the force coefficients of the pocket damper seal including the positive effective damping. From a rotordynamic viewpoint, the FPDS possesses a better liquid tolerant capability and so is a better sealing scheme for the balance piston seals and center seals of the centrifugal compressor in wet gas operating condition.