High-speed Flow Conditions Research Articles

Performance and Formula Optimization of Graphene-Modified Tungsten Carbide Coating to Improve Adaptability to High-Speed Fluid Flow in Wellbore

In order to improve the erosion resistance of steel PDC (Polycrystalline Diamond Compact) bit under high-speed fluid flow conditions underground, it is necessary to develop a high-performance erosion-resistant coating. In this paper, laser cladding was used to prepare the new coating by modifying tungsten carbide with graphene. And the effects of tungsten carbide content and graphene content on the coating performance have been thoroughly studied and analyzed to obtain the optimal covering layer. The research results indicate that, for new coatings, 60% tungsten carbide and 0.3% graphene are the optimal ratios. After adding tungsten carbide, the hardness has significantly improved. However, when the tungsten carbide content further increases more than 30%, the increase in hardness is limited. In addition, when the content of graphene is more than 0.3%, the branched structure becomes thicker. In detail, this is a phenomenon where the segregation of Cr, Si, and W becomes very obvious again, and the segregation of Fe occurs at the Ni enrichment site. The research results contribute to the development and optimization of high-quality erosion-resistant coatings under the high-speed flow conditions in wellbore. These are of great significance for improving the efficiency of oil and gas exploration and development.

Suppression of hydrofoil unsteady cavitation by periodic jets based on fish gill respiration

Cavitation is a phase change phenomenon that occurs between the liquid and vapour phases inside a homogeneous liquid or at the interface between a solid and a liquid, and the generation, collapse and shedding of cavitation are the sources of undesirable characteristics of fluid machinery. A periodic jet scheme based on the principle of bionics is designed and applied to a Clark-Y hydrofoil with a chord length of 70 mm to suppress the cavitation of fluid machinery under high-speed flow conditions. Different schemes are numerically simulated using large eddy simulation combined with the Zwart–Gerber–Belamri cavitation model to numerically simulate the different schemes. The results show that adding periodic jet to the hydrofoil can reduce the cavitation of the hydrofoil without losing the lift resistance of the hydrofoil, and the cavitation volume is 47%–52% of the original hydrofoil.

Explosive dispersal of particles in high speed environments

In this paper, we present the results of the explosive dispersal of particles in high-speed environments. We carry out Euler–Lagrange numerical simulations of a source at quiescent ambient conditions as well as moving at Mach numbers of 3 and 6. Particle volume fractions of 0%, 1%, and 4.5% are presented. The detonation profile is computed with the Jones–Wilkins–Lee equation of state using a reactive burn model. Non-static cases provide a framework to consider the effect of a bow shock and pre-existing high-speed flow conditions on the dispersal process. We also compute averages of both static and dynamic pressures, as well as impulse density histories on virtual probe planes to characterize the momentum of the flow and particles that would deposit on a target. Results suggest that the presence of the particles can have a substantial effect on the pressure average of the virtual target planes.

Aerodynamic Analysis of a Supersonic Transport Aircraft at Low and High Speed Flow Conditions

The recent improvement of technology readiness level in aeronautics and the renewed demand for faster transportation are driving the rebirth of supersonic flight for commercial aviation. However, the design of a future supersonic aircraft is still very challenging due to the complexity of several problems, such as static stability performance during the acceleration phase from subsonic speeds to supersonic speeds. Additionally, the interest of scientific community in open source numerical platform as a valid tool for a reliable and affordable aerodynamic design is considerably growing. In this framework, the present work addresses the aerodynamic performance of a Concorde-like aeroshape developed within the preliminary design of a high-speed civil transportation aircraft. Several flight conditions, ranging from subsonic to supersonic speeds, were investigated in detail by using Computational Fluid Dynamics. The aerodynamic force and moment coefficients are computed with fully three-dimensional and steady state Reynolds Average Navier-Stokes simulations, carried out in turbulent flow conditions. The effect of the Mach number variation on the shift of the aircraft aerodynamic center is detailed, by focusing on the aircraft pitching static stability. Flowfield numerical simulations are performed with both commercial (Ansys-Fluent) tool and open-source (SU2) code, which is also used extensively in multidisciplinary design procedures, for further comparisons. Particular attention is focused on the shift of the aeroshape aerodynamic center to verify that the provided wing design allows the aircraft static margin to be within 5% of the reference length, both at low-speed and high-speed flight conditions. The computed positions of the aerodynamic center are in agreement with the aeroshape surface pressure distributions and confirmed the literature results available for the Concorde aircraft. Therefore, in the view of future simulation campaigns for supersonic transportation aircraft, the present work aims to bridge the gap between previous aerodynamic design experiences, for instance matured on Concorde, and those carried out with modern CFD tools on full-scale aircraft, and on time-scales compatible with conceptual design practice. Finally, as the difference between the computed aerodynamic coefficients reflected mainly on drag computation performed with SU2, a special focus on numerical diffusion effect of the solver is also given and compared with a commercial certified CFD tool. This adds a unique further contribution to the SU2 community for aeronautics application.

Spiral instability modes on rotating cones in high-Reynolds number axial flow

This work shows the behavior of an unstable boundary-layer on rotating cones in high-speed flow conditions: high Reynolds number Rel>106, low rotational speed ratio S<1–1.5, and inflow Mach number M = 0.5. These conditions are most-commonly encountered on rotating aeroengine nose cones of transonic cruise aircraft. Although it has been addressed in several past studies, the boundary-layer instability on rotating cones remains to be explored in high-speed inflow regimes. This work uses infrared-thermography with a proper orthogonal decomposition approach to detect instability-induced flow structures by measuring their thermal footprints on rotating cones in high-speed inflow. The observed surface temperature patterns show that the boundary-layer instability induces spiral modes on rotating cones, which closely resemble the thermal footprints of the spiral vortices observed in past studies at low-speed flow conditions: Rel<105, S > 1, and M≈0. Three cones with half-cone angles ψ=15°, 30°, and 40° are tested. For a given cone, the Reynolds number relating to the maximum amplification of the spiral vortices is found to follow an exponential relation with the rotational speed ratio S, extending from the low- to high-speed regime. At a given rotational speed ratio S, the spiral vortex angle appears to be as expected from the low-speed studies, irrespective of the half-cone angle.

A Comparison of Turbulence Levels From Particle Image Velocimetry and Constant Temperature Anemometry Downstream of a Low-Pressure Turbine Cascade at High-Speed Flow Conditions

AbstractThe development and verification of new turbulence models for Reynolds-averaged Navier–Stokes (RANS) equation-based numerical methods require reliable experimental data with a deep understanding of the underlying turbulence mechanisms. High accurate turbulence measurements are normally limited to simplified test cases under optimal experimental conditions. This work presents comprehensive three-dimensional data of turbulent flow quantities, comparing advanced constant temperature anemometry (CTA) and stereoscopic particle image velocimetry (PIV) methods under realistic test conditions. The experiments are conducted downstream of a linear, low-pressure turbine cascade at engine relevant high-speed operating conditions. The special combination of high subsonic Mach and low Reynolds number results in a low density test environment, challenging for all applied measurement techniques. Detailed discussions about influences affecting the measured result for each specific measuring technique are given. The presented time mean fields as well as total turbulence data demonstrate with an average deviation of ΔTu<0.4% and ΔC/Cref<0.9% an extraordinary good agreement between the results from the triple sensor hot-wire probe and the 2D3C-PIV setup. Most differences between PIV and CTA can be explained by the finite probe size and individual geometry.

Enhanced water collection of bio-inspired functional surfaces in high-speed flow for high performance demister

Performance enhancement of thermal desalination processes requires the excellent water separation capabilities in demisters. However, in high-speed gas flow, the re-entrainment of captured water from the surfaces to the gas flow can considerably decrease the water collection capabilities and the corresponding separation efficiency. Herein, we report fabrication of micro-structured polymer surfaces with excellent water capturing properties in low- and high-speed gas flow conditions by using a facile molding process. Inspired by the surfaces of bio-species, the fabricated surfaces possess vertically-aligned micro-scale cone arrays and sets of microchannels to significantly enhance the capillary pressure. As a result, those hybrid-structured surfaces exhibit up to 2.4 and 4.7 times higher excellent water collection capabilities than control planar at low- and high-speed flow conditions, respectively. In addition, the mist eliminator with the hybrid surfaces performs 1.8 times higher water collection behavior than the control mist eliminator with bare surfaces. The results show the promise of developing the surfaces with engineered structures for significantly enhancing water collection without changing the shapes of flow passages in target objects.

Photo-responsive materials with strong cell trapping ability for light-guided manipulation of nonadherent cells.

We report a photo-cleavable material for tight trapping of nonadherent cells to substrate surfaces. Model immunocytes were selectively trapped in a non-irradiated area as single cells after the projection of a light pattern and withstood high-speed laminar flow, achieving light-guided cell release from the substrates.

Ignition enhancement by dual-pulse laser-induced spark ignition in a lean premixed methane-air flow

Ignition of fuel-lean premixed methane-air flow was investigated using single-pulse laser-induced spark (SPLIS) and dual-pulse laser-induced spark (DPLIS). Ignition enhancement was quantified with ignition probability in flow speeds and equivalence ratios of 3.75 m/s–12.5 m/s and 0.53–0.57, respectively. The range of total laser pulse energy per ignition event was 20–30 mJ. For DPLIS, the energy per pulse was half of the total energy and the time interval between pulses varied from 10 ns to 100 ns where pulse-to-pulse coupling increased the spark surface area. Broadband chemiluminescence within the visible wavelength region was used to determine ignition of the combustible mixture. The ignition probability increased with velocity for both SPLIS and DPLIS as more fuel-oxidizer mixture was exposed to the ignition source. For a fixed total energy, ignition probability was higher for DPLIS than SPLIS particularly as the equivalence ratio was increased. Depending on the flow velocity, a change in the total energy determined whether SPLIS or DPLIS had a higher ignition probability at a given flow velocity. The study showed that using DPLIS to ignite fuel-lean combustible mixtures can enhance ignition compared to SPLIS particularly at low total laser energy and high-speed flow conditions.

High-Speed Rarefied Flow Past a Rotating Cylinder: The Inverse Magnus Effect

In the present study, we investigate flow past a rotating cylinder over a wide range of flow rarefaction from the early slip through to the free-molecular regime using the direct simulation Monte Carlo method. We focus specifically on high-speed flow conditions and consider a wide range of Mach numbers near the high subsonic, transonic, and supersonic regimes. Various flow parameters such as the coefficients of lift and drag as well as the coefficients of pressure, skin friction, and wall heat transfer have been investigated as a function of both the Mach number and the Knudsen number to gain insight into the flow physics in the different regimes. The flow characteristics in the transonic regime have been found to be substantially different from those in the supersonic regime. In particular, an inverse Magnus effect involving a change in the direction of the lift force occurs in the supersonic regime. In contrast, subsonic flows in the early slip-flow regime experience the conventional direction for the Magnus lift force. This paper demonstrates that there is a subtle interplay between the Mach number and Knudsen number for the occurrence of the inverse Magnus effect.

Bubble Collapsing Behavior of Vortex Cavitation Ralative to Erosion Especially in the Near Wake behind a Triangular Cylinder.

It is known that erosion of fluid machinery can be caused by collapes of a cavitation bubble under high speed flow conditions. To solve this cavitation erosion problem, we performed some experiments on the cavitation process from a subcavitation to a supercavitation stage with a measurement system combining a high-speed video camera and an impulsive pressure sensor. This study focuses in particular on a vortex cavitation bubble in the near wake of a triangular body at the partially cavitating stage which is well known as a highly erosive pattern. Erosion tests were conducted regarding the mechanism of highly impulsive force generation, and bubbl collapsing behaviors were observed. The results show that three characteristic patterns of bubble collapse and erosion occur within the near-wake region.

Evidence for a structure-free state at high solar wind speeds

The variability of the basic solar wind flow parameters in highand low-speed flows is submitted to a statistical analysis. Particular attention is given to the uniformity of solar wind high-speed flow conditions by comparing them with those of the low-speed so-called quiet solar wind. With the exception of the solar wind bulk velocity, the average fractional variation of each of a selected sample of basic solar wind parameters is found to be substantially larger during low-speed flow conditions than during high-speed flow conditions at 1 AU. As a statistical ensemble of events, the only thing steady and uniform about low-speed conditions is the bulk velocity. In all other respects, high-speed flows form a much more uniform ensemble of solar wind conditions than do the low-speed flows. It is concluded that the use of average high-speed flow parameters for comparison with steady-state spherically symmetric models of the coronal expansion is meaningful.

Oxidation behavior of TD-NiCr in a dynamic high temperature environment

The oxidation behavior of TD-NiCr has been studied in static and high-speed flowing air environments at 1100 and 1200°C. The surface oxide topographies and microstructures formed in both types of environments have been characterized and compared to explain some of the observed differences in the oxidation behavior for the two types of tests. It has been found that the stable oxide morphologies formed on the specimens exposed to the static and dynamic environments were markedly different. The faceted crystal morphology characteristic of static oxidation was found to be unstable under high-temperature, highspeed flow conditions and was quickly replaced by a porous NiO “mushroom” type structure. Also, it was found that the rate of formation of CrO3(v) from Cr2O3(s) was greatly enhanced by high gas velocity conditions. The stability of Cr2O3 was found to be greatly improved by the presence of an outer NiO layer, even though the NiO layer was very porous. An oxidation model is proposed to explain the observed microstructures and overall oxidation behavior of TD-NiCr alloys.