The evolution of surface profiles during erosion caused by the continuous impact of a liquid jet was studied using a water-jet apparatus. In this study, we focused on the erosion transition from the ...incubation stage to the accumulation stage during liquid impingement erosion, which is important for water-jet cleaning and aging management for nuclear power plants. By computing the local erosion rate distribution and surface roughness parameters, the formations of isolated pits and asperities were investigated. The structure of erosion caused by liquid impingement was extracted by using a dynamic mode decomposition technique. The surface profile changes were primarily caused by the formation of isolated pits and asperities during the incubation stage. The roughness parameters remained unchanged during the incubation stage, with barely measurable erosion depth, whereas the skewness of the surface profile began to increase during this stage. The initial erosion with a small-scale roughness gradually evolved into a large-scale crater. Dynamic mode decomposition analysis showed the presence of a short-wavelength (mode A) surface depression during the incubation stage, followed by a long-wavelength (mode B) erosion crater caused by the merging of mode A surface depressions during the accumulation stage.
•Erosion stage transition in liquid impingement erosion was experimentally studied.•Dynamic mode decomposition method was employed to analyze the erosion stage transition.•Erosion stage transitions were highly correlated with the roughness parameters and modes.
•High-speed liquid droplet impact on a planar rigid wall was numerically studied.•Time-dependent force and droplet pressures were computed and analyzed.•Oscillatory behavior of the time-dependent ...force was caused the reverberation inside the droplet.•Increased time-dependent force was observed with increasing droplet impact velocity.
In this study, the effect of the impact velocity of a droplet on the time-dependent force exerted on the droplet and droplet pressure during high-speed O (100 m/s) liquid droplet impingement (LDI) on a planar rigid wall is numerically investigated. The force exerted on the droplet and droplet pressures are computed as a function of time, and its frequency spectrum is analyzed to explain the physical mechanisms that occur during high-speed LDI. The results show that high-speed LDI involves the formation of a water hammer shock and its reflection on the free surface of the droplet and wall, resulting in sustained reverberation inside the droplet. Therefore, the force curve shows oscillatory behavior and is quite different from that of the low-speed O (1 m/s) impact case. Finally, the force and the droplet pressure are computed for various impact velocities of the droplet.
•Numerical simulations of the high-speed droplet impact on a wet wall were carried out.•Mechanism of force generation in droplet and liquid film were investigated.•Force exerted on droplet decreases ...with increasing liquid film thickness.•Force exerted on liquid film increases with increasing liquid film thickness.
Recent research (Fujisawa, 2022a) has shown that the time-dependent force exerted on a droplet during high-speed O (100 m/s) impact on a planar rigid wall is quite different from that of low-speed O (1 m/s) impact case owing to the compressibility of the droplet. Here, we consider a more general case of a high-speed liquid droplet impacting a wall where a liquid film is present on the wall surface. Three-component Euler simulations were performed to determine the characteristics of the time-dependent force exerted on the droplet during high-speed liquid droplet impact on a planar rigid wet wall. Several initial liquid film thicknesses were considered. The strength of the force exerted on the droplet decreases in magnitude as the liquid film thickness increases, whereas the total force increases with increasing liquid film thickness owing to the presence of a water hammer shock that is reflected inside the liquid film.
We study the piston problem for the compressible fluid flow of generalized Chaplygin gas, for both cases that the piston rushes into or recedes from the uniform still gas at a constant speed. The ...global existence of a solution to the piston problem is established. For the proceeding piston problem, we find that the front shock can be detached or adhered to the surface of the piston depending on the range of Mach numbers. Then, a Radon measure solution, with density containing a Dirac measure supported on the piston is rigorously defined and proved to be a reasonable solution to deal with the concentration of mass on the piston. When the piston recedes from the gas, we show strictly that only a first-family rarefaction wave exists in front of the piston and that concentration will never occur. Moreover, we also analyzed the occurrence of the vacuum state and the degeneration of the compressible fluid flow in the receding case as the Mach number tends to infinity.
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•Singularity formation of compressible flow is observed as the piston pushes forward.•A reasonable Radon measure solution is defined to describe the singular phenomenon.•For receding piston problem, global existence of one rarefaction wave is proved.
•Compressible multicomponent flow simulations of high-speed LDI are conducted for various impact Mach numbers.•A self-similar structure for the pressure field is observed.•A data-driven approach for ...realistic and quick simulations of high-speed LDI is presented.
Accurate prediction of the force exerted on a droplet during high-speed liquid droplet impingement (LDI) is challenging yet important for the safety management of nuclear/fossil power plants. This paper describes compressible multicomponent flow simulations and data-driven modeling of high-speed LDI. The compressible multicomponent flow simulations are conducted for various impact Mach numbers ranging from Ma = 0.045 to 0.077. Whereas the peak force associated with the water hammer shock exhibits dependency on the impact Mach number, a self-similar structure for the pressure field within the small region about the impact plane is observed during high-speed LDI. An important observation is that the nondimensional mass-averaged droplet velocity does not vary with the impact Mach number. Finally, a data-driven LPP approach is presented to obtain fast and highly realistic simulations of high-speed LDI.
The objective of the study is realizing the effect of fuel mass flow rate and flight speed on combustion in scramjet engine. DLR conical strut based scramjet combustor configuration was chosen and ...simulated the chemical reaction between the air and hydrogen fuel. A slot of size 40 mm × 0.295 mm provided at the center of the strut to injected hydrogen fuel from the rare side in to the downstream flow. ICEM CFD software is used for the generation of structured elements in computational domain for three dimensional flow analyses. Standard k-epsilon turbulence model and species transport equation is used in ANSYS fluent solver. The predicted temperature, velocity distribution along the axial length was compared with the experimental results and validated. The temperature distribution at different Mach numbers and mass flow rate reveals that the peak temperature increased with the flight speed and inlet fuel mass flow rate. The peak temperature noticed at the center of the combustor is around 3500 K at a flight speed of Mach 4. The predicted variation of temperature, pressure, velocity in the combustor and the flow structure for reacting flow facilitate good understanding of the combustion process in scramjet combustor.
This paper introduces a virtual boundary method for compressible viscous fluid flow that is capable of accurately representing moving bodies in flow and aeroacoustic simulations. The method is the ...compressible extension of the boundary data immersion method (BDIM, Maertens & Weymouth (2015), 18). The BDIM equations for the compressible Navier–Stokes equations are derived and the accuracy of the method for the hydrodynamic representation of solid bodies is demonstrated with challenging test cases, including a fully turbulent boundary layer flow and a supersonic instability wave. In addition we show that the compressible BDIM is able to accurately represent noise radiation from moving bodies and flow induced noise generation without any penalty in allowable time step.
In this paper, we study the limiting behavior of Riemann solutions to the Euler equations of one-dimensional compressible fluid flow as γ tends to one. We show that the limit solution forms the delta ...wave to the pressureless Euler system of one-dimensional compressible fluid flow in the distribution sense. Some numerical results exhibiting the phenomena of concentration are also presented.
Abstract
The objective of the study is realizing the effect of fuel mass flow rate and flight speed on combustion in scramjet engine. DLR conical strut based scramjet combustor configuration was ...chosen and simulated the chemical reaction between the air and hydrogen fuel. A slot of size 40 mm × 0.295 mm provided at the center of the strut to injected hydrogen fuel from the rare side in to the downstream flow. ICEM CFD software is used for the generation of structured elements in computational domain for three dimensional flow analyses. Standard k-epsilon turbulence model and species transport equation is used in ANSYS fluent solver. The predicted temperature, velocity distribution along the axial length was compared with the experimental results and validated. The temperature distribution at different Mach numbers and mass flow rate reveals that the peak temperature increased with the flight speed and inlet fuel mass flow rate. The peak temperature noticed at the center of the combustor is around 3500 K at a flight speed of Mach 4. The predicted variation of temperature, pressure, velocity in the combustor and the flow structure for reacting flow facilitate good understanding of the combustion process in scramjet combustor.
•We propose a dimensionless numerical mesh-free model.•The formulation os the Navier-Stokes equations is a dimensionless form.•The performance of the presented model is tested on the standard ...benchmark lid-driven cavity problem.
In this paper, we propose a dimensionless numerical mesh-free model for the simulation of the compressible isothermal viscous flows. The novelty of this work consists to formulate the Navier-Stokes equations under a dimensionless form and to solve them by a high order mesh-free algorithm to simulate the compressible fluid flows. This algorithm combines a classical implicit Euler scheme, a high order continuation with the Moving Least Squares (MLS) and a homotopy transformation. The MLS approximation and implicit Euler scheme are used respectively for the spatial and temporal discretizations of dimensionless Navier-Stokes equations. The homotopy transformation serves to introduce in dimensionless Navier Stokes equations an arbitrary operator and a parameter without physical dimension. The obtained equations are solved by a high order continuation. The performance of the presented model is tested on the standard benchmark lid-driven cavity problem. Then, the Mach and Reynolds numbers effect is discussed. The obtained results are compared with those of the Finite Difference Method (FDM) coupled with an explicit Runge-Kutta (R-K) scheme and those of literature. This comparison reveals that the results of the dimensionless model are obtained with a less expensive CPU time compared to that of the other algorithms.
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