A finite-volume method is developed for simulating the mixing of turbulent flows at transcritical conditions. Spurious pressure oscillations associated with fully conservative formulations are ...addressed by extending a double-flux model to real-fluid equations of state. An entropy-stable formulation that combines high-order non-dissipative and low-order dissipative finite-volume schemes is proposed to preserve the physical realizability of numerical solutions across large density gradients. Convexity conditions and constraints on the application of the cubic state equation to transcritical flows are investigated, and conservation properties relevant to the double-flux model are examined. The resulting method is applied to a series of test cases to demonstrate the capability in simulations of problems that are relevant for multi-species transcritical real-fluid flows.
•The internal pressure curves all present two typical pressure peaks.•The methane concentration and PV have the effect on the venting flow velocity.•The pressure oscillation is noticed in the ...internal pressure curves when methane concentration is from 9 vol% to 13 vol%.•The internal temperature curves, the change of methane concentration and venting flow velocities are analyzed.
This paper presents the experiments and numerical simulation of vented methane-air explosion. The influence of methane concentration and vent burst pressure on the internal pressure dynamic and venting characteristic is investigated. The pressure oscillation is hardly noticed in the internal pressure curve as the case of concentration is 7 vol%. But for the case of concentration is from 9 vol% to 13 vol%, the pressure oscillation is obvious in the internal pressure curves. Two internal temperature peaks are found in the three simulated temperature curves. The duration of internal temperature curve will increase with the increase of methane concentration. The methane concentration and vent burst pressure have the influence on the variation curve of the internal fuel concentration. When the methane concentration is 7 vol%, it is worth noting that the internal fuel concentration drops rapidly to zero after vent opening. And when the methane concentration is 9 vol% or 11 vol%, the internal fuel concentration has a dramatic decrease and then maintains a slow descent after vent opening. The internal pressure curves with different concentrations all present two typical pressure peaks. The first pressure peak is more noteworthy than anther one under higher vent burst pressure conditions; the second pressure peak is more important under lower vent burst pressure conditions.
A liquid droplet dispensed over a sufficiently hot surface does not make contact but instead hovers on a cushion of its own self-generated vapor. Since its discovery in 1756, this so-called ...Leidenfrost effect has been intensively studied. Here we report a remarkable self-propulsion mechanism of Leidenfrost droplets against gravity, that we term Leidenfrost droplet trampolining. Leidenfrost droplets gently deposited on fully rigid surfaces experience self-induced spontaneous oscillations and start to gradually bounce from an initial resting altitude to increasing heights, thereby violating the traditionally accepted Leidenfrost equilibrium. We found that the continuously draining vapor cushion initiates and fuels Leidenfrost trampolining by inducing ripples on the droplet bottom surface, which translate into pressure oscillations and induce self-sustained periodic vertical droplet bouncing over a broad range of experimental conditions.
Rotating detonation engines (RDEs) have received significant attention from industry and academia alike, owing to their numerous advantages, such as pressure gain combustion, high operation ...frequency, and near-constant thrust output. Furthermore, there is considerable interest in combining RDEs with gas-turbine engines to further improve their overall system performance. This study examines the propagation characteristics of continuous rotating detonation waves (CRDWs) with a turbine guide vane (TGV). We develop an experimental model of a hydrogen–air rotating detonation combustor integrated with a TGV section and record the high-frequency pressure oscillations and static pressure upstream and downstream of the TGV section. The experimental results indicate that: the interactions between CRDW and the turbine blade cause the reflected shock propagating backwards to the combustor. Both pressure oscillation amplitude and static pressure decline at downstream of TGV. Notably, the pressure oscillation attenuation by the TGV is influenced by the direction of CRDW propagation. When the CRDW propagation direction and the flow path direction of the guide vane are opposite to each other, the pressure oscillation attenuation increases. The findings obtained herein provide benchmark data that help improve the fundamental understanding of CRDW and TGV interaction, and can be used to develop detonation-based propulsion technology.
•Rotating detonation combustor integrated with a turbine model to improve performance.•Verification of rotating detonation combustor operation characteristics.•Detailed discussion of interactions between the rotating detonation wave and turbine blade.•Quantitative analysis of pressure oscillation across the turbine under various conditions.•Relationship between pressure amplitude attenuation and detonation propagation direction.
•Condensation induced water hammer (CIWH) regime maps under different pipe lengths were obtained.•Transition criterion of periodic CIWH considering pipe length was developed.•Frequency correlation of ...periodic CIWH considering pipe length was developed.•Correlation of the occurrence position of periodic CIWH was developed.
Condensation induced water hammer (hereafter, CIWH) phenomenon is widely observed in various industrial operations, causing severe damage to related equipment and personal safety. This study investigated the CIWH regime map and the oscillation characteristics of periodic CIWH under different pipe lengths when the steam was discharged into a water tank through a horizontal pipe. First, the CIWH regime maps were obtained under different pipe lengths, with distinct regimes of periodic CIWH and non-periodic CIWH. A criterion was proposed to predict the transitions from periodic to non-periodic CIWH. It was found that the occurrence frequency of periodic CIWH decreased with the increase in the pipe length. An empirical correlation of Strouhal number, non-dimensionalized occurrence frequency, was developed to predict the occurrence frequency. The correlation could reproduce more than 95 % of the experimental data with the error of -20.2 % to 23.7 %. The pressure oscillation intensity of periodic CIWH was analyzed. The oscillation intensity increased when the pipe length and steam mass flux increased, whereas it increased first and then decreased when pool temperature increased. Finally, the occurrence position of periodic CIWH was found to be nearly constant under the same test condition. The position moved downstream of the steam when the pipe length and Froude number increased, and Jakob number decreased. The average occurrence position was correlated with the error of -17.1 % to 18.4 %.
•The initial volume of entrapped bubble for periodic CIWH was analyzed.•The change laws of volume change rate of entrapped bubble were obtained.•A theoretical correlation of pressure oscillation ...intensity of CIWH was proposed.
Steam condensation-induced water hammer (CIWH) can cause great pressure oscillation, and the knowledge of CIWH is important to pipes and relevant equipment. In this work, an experiment was conducted to investigate the condensation process of entrapped bubbles for periodic CIWH and its pressure oscillation in a horizontal pipe. Results indicated that CIWH was caused by the condensation of entrapped bubbles, and the initial volume of entrapped bubbles of the periodic CIWH kept nearly unchanged when the test conditions were constant. The initial bubble volume increased with the increases in steam mass flux and water temperature. The pressure oscillation intensity of the CIWH increased with the increase in initial bubble volume but decreased with the increase in water temperature. Furthermore, the change rate of bubble volume gradually increased with the condensation of the entrapped bubbles. The final change rate of bubble volume increased with the increase in initial bubble volume but decreased with the increase in water temperature. Finally, a theoretical correlation, that is, a linear relationship between the pressure oscillation intensity and the final change rate of bubble volume, was proposed to calculate the pressure oscillation intensity of the CIWH. The predicted deviation ranged from −44% to 64%.
An experimental study has been conducted to investigate the characteristics of subsonic steam jet condensation pressure oscillations in the ranges of steam mass flux 50–90 kg/m2s, water temperature ...20–90 °C and vessel pressure 0.1–0.4 MPa. High-frequency dynamic pressure and high-speed images of the steam bubble condensation process are recorded and analyzed. It is found that the steam bubble necking frequency increases with steam mass flux and decreases with water temperature. The vessel pressure also has an effect on the steam bubble necking frequency. The pressure oscillation intensity in the pipe increases with the steam mass flux in the condensation oscillation region, but the trend in the chugging region is opposite. The vessel pressure can strengthen the internal pipe pressure oscillation in the chugging region. The pressure oscillation intensity in the pool increases initially, but then decreases rapidly with the water temperature. The water temperature where the pressure oscillation intensity becomes maximum shifts lower with increasing vessel pressure. An equation correlating the Strouhal number, Reynolds number and Jakob number is developed and can predict the experimental data obtained under 0.1 MPa vessel pressure with a deviation within ± 10%. A dimensionless pressure term is added in the correlation to be applied for 0.2–0.4 MPa conditions and the maximum discrepancy between the predicted values and experimental results is within ± 15%.
•Experiments for pure steam and air-steam mixture gas jets are performed.•The effect of different parameters on pressure oscillation characteristics is discussed.•New correlations for pressure ...oscillation dominant frequency are developed.•New correlations for pressure oscillation intensity are developed.
The pressure oscillation is an important characteristic of direct contact condensation of steam in subcooled water. Many experimental works have been performed on pure steam submerged jet condensation. However, the effect of non-condensable gas content on the characteristics of the pressure oscillation is not yet fully understood. So, present paper aims to investigate the effect of air mass fraction on the characteristics of the pressure oscillation. Experimental results show that: for pure steam jets, the pressure oscillation dominant frequency decreases with the rise of water temperature and nozzle diameter. While it increases with the rise of steam mass velocity, which is consistent with the most of previous research results. The pressure oscillation intensity increases with the rise of water temperature, steam mass velocity and nozzle diameter. For air-steam mixture gas jets, the effect of water temperature and steam mass velocity on pressure oscillation characteristics is the same as pure steam jets. The pressure oscillation dominant frequency rapidly decreases with the rise of air mass fraction. However, air mass fraction has a complex effect on pressure oscillation intensity. As the air mass fraction increases, the pressure oscillation intensity rapidly increases at first, then slowly decreases and then slowly increases. In addition, new correlations for pressure oscillation dominant frequency and intensity are developed. The predicted results agree well with the experimental results.
•Importance of an appropriate crack tip advancement/time stepping algorithm.•Possible pitfalls with inappropriate algorithms.•Crack forerunning as an additional source of stepwise crack tip ...advancement.•Continuum models can indeed capture stepwise crack tip advancement.
•Bubble resonance with 35 Hz is observed, which could intensify pressure oscillation intensity.•Air is present in dispersive small bubbles or a toroid after condensation.•The onset of chugging is ...given by correlations.•A new frequency correlation modified with probability is developed.
An experimental study is conducted on the condensation behavior, onset of chugging, fluid oscillation, and pressure oscillation when a steam–air mixture is injected vertically into subcooled water at a low mass flux. Air is present in the form of dispersive small bubbles after condensation at a low water temperature and in the shape of a toroid at a high water temperature. Bubble resonance is first observed experimentally; a large bubble is almost stationary below the pipe outlet and air is sustainably released by small bubbles from the upper surface. The upper air mass fraction of chugging is obtained and compared with a transient conduction–diffusion model and momentum balance model. The dependence of different parameters on the amplitude, frequency, and probability of fluid oscillation is analyzed. A new frequency correlation modified with probability is developed and shows good agreement with the experimental data. During bubble resonance, the wave shape of pressure oscillation is harmonic with the frequency at about 35 Hz, and the intensity is larger than that under pure steam conditions. When bubble resonance does not occur, the presence of air can reduce the pressure oscillation intensity.
PDF
