Wave Rotor Research Articles

Experimental Research of the Entire Wave System Inside a Wave Rotor Refrigerator and the Impact of Pressure Ratios on the Equipment Performance

Abstract The wave rotor refrigerator (WRR) is an efficient refrigeration technology. For the purpose of investigating the gas wave characteristics inside the rotor channels of WRR device, the performance and pressure monitoring experiments were conducted at various pressure ratios in this study, and the main findings are as follows: the computation method can produce an accurate design of pressure ports though the post-wave gas pressure of numerical computation has a certain difference with the experiment because of the actual gap leakage and friction loss. The deviation of working pressure ratio from the design values results in the reversed/reflected compression waves or worsens gas leakage, which lowers the equipment performance. When the expansion ratio α is constant, the efficiency reduction ratio does not exceed 11.9% as the relative variation rate of the compression ratio is less than 150%; When the compression ratio β is constant, the efficiency is relatively lowered by a proportion less than 16.4% as the relative increasing ratio of α is less than 63%. This study improves the mechanism of WRR and demonstrates the strong ability of WRR to resist fluctuations in working conditions.

The role of pulse timing in cardiac defibrillation.

Life-threatening cardiac arrhythmias require immediate defibrillation. For state-of-the-art shock treatments, a high field strength is required to achieve a sufficient success rate for terminating the complex spiral wave (rotor) dynamics underlying cardiac fibrillation. However, such high energy shocks have many adverse side effects due to the large electric currents applied. In this study, we show, using 2D simulations based on the Fenton-Karma model, that also pulses of relatively low energy may terminate the chaotic activity if applied at the right moment in time. In our simplified model for defibrillation, complex spiral waves are terminated by local perturbations corresponding to conductance heterogeneities acting as virtual electrodes in the presence of an external electric field. We demonstrate that time series of the success rate for low energy shocks exhibit pronounced peaks which correspond to short intervals in time during which perturbations aiming at terminating the chaotic fibrillation state are (much) more successful. Thus, the low energy shock regime, although yielding very low temporal average success rates, exhibits moments in time for which success rates are significantly higher than the average value shown in dose-response curves. This feature might be exploited in future defibrillation protocols for achieving high termination success rates with low or medium pulse energies.

Flow and Combustion Characteristics of Wave Rotor–Trapped Vortex Combustor System

Breaking through the limit of conventional compression and combustion, wave rotor and trapped vortex combustors are able to improve the thermal efficiency of gas turbines. Detailed two-dimensional numerical simulations based on Ansys Fluent were performed to study the flow and combustion characteristics of the wave rotor–trapped vortex combustor system. The calculated pressure characteristics agree with the experimental results giving a relative error for average pressure of 0.189% at Port 2 and of 0.672% at Port 4. The flow stratification characteristics and the periodic fluctuations were found to benefit the zonal organized combustion in the trapped vortex combustor. For the six cases of different rotor speeds, as the rotor speed increased, the oxygen mass fraction at the combustor inlet rose and then fell. The proportion of exhaust gas recirculation fell at first and then rose, and the combustion mode became unstable with the dominant frequencies of the fluctuations increasing.

Wave rotor as a pressure exchanger for lower rotational speed and lower shaft work in a supercritical carbon dioxide Brayton cycle

Supercritical carbon dioxide Brayton cycle is emerging as a solution to effective and clean power resources, and the pressure exchanger is a critical part of such cycle. While turbomachinery is the conventional technology of such pressure exchangers, it sustains high shaft work and suffers from especially high rotational speed, which is a key challenge. This work proposed a wave rotor for supercritical carbon dioxide pressure exchanger as an alternative technology of the turbomachinery. Numerical simulation results demonstrate that a wave rotor compresses and expands supercritical carbon dioxide with unsteady pressure waves, so it does not take a high rim speed to do the compression or expansion work like turbomachinery, and a low rotational speed and a low shaft work are available then. According to the design results for a practical compression ratio at 1.93 and a massflow rate at 2.30 kg/s, the wave rotor reduces the rotational speed to 8 % and the shaft work to 4 % of equivalent turbomachines, and the wave rotor has comparable efficiency and size to equivalent turbomachines. This work provides the special advantage and suitability of the wave rotor as a pressure exchanger of the supercritical carbon dioxide Brayton cycle.

Effect of Stagger Angle of Rotor Channels on the Wave Rotor

A wave rotor optimizes the use of energy resources by enhancing thermodynamic cycles, and further optimization of wave rotor geometry is emerging as an attractive research area. Among the geometric features, the stagger angle of channels lacks sufficient study in spite of its important effects. To address this question, this work developed and applied the velocity triangle models to modify the basic geometry of wave rotors for different stagger angles, and investigated the flow fields with two-dimensional numerical methods. Results showed that: (1) different stagger angles worked out similar unsteady pressure wave systems and kept nearly constant compression and expansion ratios of the wave rotor; (2) increased stagger angle made the inlet and outlet flows turn toward the axial direction, which was beneficial to compact and light-weighted integration of the wave rotor to a gas turbine; (3) increased stagger angle made the wave rotor consume more shaft power, but even the maximum shaft power was small. This work revealed a critical mechanism how the velocity variation across an unsteady pressure wave produced rim work in a staggered channel, and made a recommendation to comprehensive optimization of wave rotor geometry for better integration in a gas turbine and acceptable shaft power consumption.

An internal model control method for wave rotor refrigeration process based on Harris hawks optimization

A novel internal model control (IMC) method for wave rotor refrigeration process (WRRP) based on Harris hawks optimization (HHO) is presented in this paper. Firstly, an identification model is established by the test data of the WRRP. In order to reduce the complexity of the model, the Routh order reduction method was used to reduce the order of the identification model. This procedure yields an approximate second order model with time delay for the WRRP. Secondly, an IMC method based on HHO is proposed after analyzing the time delay characteristics of the WRRP model. This method improves the traditional IMC structure, and introduces a three degree of freedom IMC structure. The parameters of the controller are optimized by HHO to make the comprehensive performance index of the system reach the best. Simulation results demonstrate that the proposed method can achieve a good performance of tracking and disturbance rejection.

Experimental and Numerical Research on Strengthening the Performance of Wave Rotor Equipment with Curved Passages

Experimental and Numerical Research on Strengthening the Performance of Wave Rotor Equipment with Curved Passages

Rubbing vibration characteristics of double-rotor system under wave load

Structural characteristics of a certain type of gas turbine double rotor and its hull are analyzed. The wave of a regular form is considered, and the wave load is simplified to the form of sinusoidal force. The rubbing force and nonlinear supporting force of the bearing are deduced as per the Hertz contact theory and Coulomb friction law. The mechanical model of the double rotor system under the combined action of the wave load and rotor friction impact is established, which is solved by the fourth-order Runge-Kutta method. The bifurcation diagram, phase diagram, Poincare section diagram, axis trajectory diagrams, effects of rotor eccentricity, and friction coefficient on the nonlinear dynamic characteristics of the system under rub impact fault are studied. The obtained results show that with an increase in eccentricity, the system enters into a chaotic state through the period doubling and paroxysmal bifurcations, and successively experiences nonlinear behaviors such as periodic 2 bifurcation, periodic 4 bifurcation, and quasi periodic and chaos. In the double rotor system, the nonlinear dynamic behavior of the single period and semi Nermark-Sacker bifurcation occurs with increasing friction coefficient. The present findings can provide a theoretical basis for condition monitoring, fault diagnosis, and design optimization of this type of gas turbine double rotor system.

Heterotypic Cx43/Cx45 gap junction channel conductance depends on pulse rate and could rescue from arrhythmogenic activity in cardiac tissue

Abstract Introduction Gap junction (GJ) channels, formed of connexin (Cx) proteins, conduit electrical excitation in the heart. It is well established that GJ conductance (gj) depends on transjunctional voltage (Vj), but little is still known about its dynamics during the spread of cardiac excitation. Transitional tissue of atrioventricular (AV) node expresses Cx43 and Cx45, which could form heterotypic GJs, which are highly sensitive to Vj. Purpose Evaluation of heterotypic gj dynamics of Cx43/Cx45 channels during the propagation of excitation in cardiac tissue. Methods The CE-4SM model of cardiac tissue, consisting of discrete cells connected through dynamic GJs, was developed by combining Fenton-Karma equations, which define cardiac excitability (CE), and a 4-state model (4SM) of GJ channel gating, which describes the dependence of gj on Vj and its kinetics. Global optimization methods were applied for 4SM parameter evaluation to fit gj timecourses obtained from electrophysiological recordings. Experiments were performed using dual-whole-cell patch clamp in Novikoff cells, endogenously expressing Cx43, and Hela cells transfected with Cx45. Results We developed a combined cardiac excitability model (CE-4SM), that allowed us to study an interaction between the spread of cardiac excitation and GJ channel voltage. Modeling results shows that during propagation of excitation, the phase difference between each action potential (AP) in adjacent cells, generates two subsequent Vj spikes. First spike causes small decrease of gj, while the second one, a minor increase. These impulses can accumulate into a large overall decay until the impulse rate-dependent steady-state is reached. This phenomenon is caused by variation of delays between APs and consequentially, different durations and amplitudes of Vj spikes developed across GJ channels. Interestingly, such gj decrease was capable of causing drift of spiral wave rotor or termination of fibrillation-like arrhythmia during our modeling experiments. Also, we performed in-vitro experiments to evaluate 4SM model parameters and validate simulation results that showed gj decay at a high pulse rate, which could occur during reentry-like tachycardia. Conclusions Voltage gating of Cx43/Cx45 GJ channels could act as a control circuit, that lowers gj between the transitional cells of AV node at high impulse rate. Presumably, this could help to reduce the conduction or even act as a block of high-rate impulses passing through AV node. Also, such gj decrease could cause a drift of spiral waves and disruption of fibrillation-like processes. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): Lithuanian University of Health Sciences, Institute of Cardiology

Research on rotational speed affecting the expansion performance of wave rotor

Research on rotational speed affecting the expansion performance of wave rotor

Numerical Study on the Effect of Nozzle Incident Angle on the Overall Performance of Gas Wave Refrigerator

Gas wave refrigerator (GWR) is a new type of refrigeration machinery that uses pressure waves to transfer energy between gases. In this paper, the flow characteristics and refrigeration mechanism in the wave rotor are numerically simulated. The nozzle angle is introduced to improve the overall refrigeration performance and expand the efficient operating range of the equipment. After verifying the model and method, the potential mechanism of refrigeration loss in the oscillating tube and the effect of loss on refrigeration efficiency are discussed in detail. Then the influence of incident angle on flow loss, refrigeration temperature drop, and power consumption are discussed. The association model of velocity development pattern and the maintenance of pressure performance at the inlet position of the oscillating tube is established during the high-pressure gas incident. The obtained numerical results show that flow loss and shock intensity loss are the main energy loss factors in the wave rotor. The incident angle determines the loss of the refrigeration process. The optimal incident angle of the device at the working point is obtained. The "balance" of velocity distribution in the oscillating tube can effectively reduce vortex loss. Arranging nozzles in the same rotation direction as the wave rotor can reduce work consumption, and the variation law is approximately negative linear correlation. Furthermore, based on the current simulation results, a set of nozzle design methods are obtained. It laid the foundation for the subsequent experimental research and optimization of GWR equipped with adaptive nozzles.

Electrophysiology and Arrhythmogenesis in the Human Right Ventricular Outflow Tract.

Right ventricular outflow tract (RVOT) is a common source of ventricular tachycardia, which often requires ablation. However, the mechanisms underlying the RVOT's unique arrhythmia susceptibility remain poorly understood due to lack of detailed electrophysiological and molecular studies of the human RVOT. We conducted optical mapping studies in 16 nondiseased donor human RVOT preparations subjected to pharmacologically induced adrenergic and cholinergic stimulation to evaluate susceptibility to arrhythmias and characterize arrhythmia dynamics. We found that under control conditions, RVOT has shorter action potential duration at 80% repolarization relative to the right ventricular apical region. Treatment with isoproterenol (100 nM) shortened action potential duration at 80% repolarization and increased incidence of premature ventricular contractions (P=0.003), whereas acetylcholine (100 μM) stimulation alone had no effect on action potential duration at 80% repolarization or premature ventricular contractions. However, acetylcholine treatment after isoproterenol stimulation reduced the incidence of premature ventricular contractions (P=0.034) and partially reversed action potential duration at 80% repolarization shortening (P=0.029). Immunolabeling of RVOT (n=4) confirmed the presence of cholinergic marker VAChT (vesicular acetylcholine transporter) in the region. Rapid pacing revealed RVOT susceptibility to both concordant and discordant alternans. Investigation into transmural arrhythmia dynamics showed that arrhythmia wave fronts and phase singularities (rotors) were relatively more organized in the endocardium than in the epicardium (P=0.006). Moreover, there was a weak but positive spatiotemporal autocorrelation between epicardial and endocardial arrhythmic wave fronts and rotors. Transcriptome analysis (n=10 hearts) suggests a trend that MAPK (mitogen-activated protein kinase) signaling, calcium signaling, and cGMP-PKG (protein kinase G) signaling are among the pathways that may be enriched in the male RVOT, whereas pathways of neurodegeneration may be enriched in the female RVOT. Human RVOT electrophysiology is characterized by shorter action potential duration relative to the right ventricular apical region. Cholinergic right ventricular stimulation attenuates the arrhythmogenic effects of adrenergic stimulation, including increase in frequency of premature ventricular contractions and shortening of wavelength. Right ventricular arrhythmia is characterized by positive spatial-temporal autocorrelation between epicardial-endocardial arrhythmic wave fronts and rotors that are relatively more organized in the endocardium.

Investigation on wave system matching of two-phase pressure oscillation tube

Non-equilibrium phase transition will take place in the pressure oscillation tube if the intake of wave rotor refrigerator (WRR) contains condensable components, which will affect intensity and speed of the wave system in the tube, and further affect the port matching of WRR. In this paper, numerical model of non-equilibrium phase transition is established and the effects on intensity of the wave system and the port matching is studied. The properties of polar gas are described by the cubic-plus-association (CPA) gas state equation, improving the accuracy of computational fluid dynamics (CFD) calculations. By using the model, the design precision of two-phase WRR is improved. Besides, the results of numerical simulation are verified by experiments.

Investigations of pressure field along a channel of a pressure wave supercharger

The aim of the paper is a numerical investigation of the evolution of the pressure field along the wave rotor channels of a pressure wave ICE supercharger. In the present literature, most of the studies are considering the fluids as incompressible and inviscid in a 2D field. The present study is using the compressible and viscous terms in the unsteady Lattice Boltzmann method for fluid in a 3D field. The geometry was drawn in CAD software using measurements made on a real model of the CX-93 pressure wave supercharger. The simulation was conducted using a code for native unsteady LBM approach to reproduce data such as pressures, temperature and mass flows, which are usually hard to be measured in a real pressure wave supercharger. The computational domain was modelled as a moving rotational domain with adaptive refinement. Results such as velocity, pressure and temperature field in the rotor channels were obtained for exhaust gas inlet pressure of 0.292 MPa and 721 K temperature at different rotational speeds. The air inlet state considered was: 0,096 MPa and 313 K. The simulated values obtained are similar to the reported experimental results found in the literature showing a good concordance with the model.

Numerical investigation of a pressure wave supercharger

The paper aims at a numerical investigation of the evolution of velocity, pressure and temperature field along the wave rotor channels for a pressure wave supercharger. Since in literature most of the studies are made considering the working fluid as incompressible and inviscid in a 2D field, the present study is using the compressible and viscous terms in unsteady Navier-Stokes equations for fluid in 3D field. The geometry was drawn in CAD software using measurements made on a real model of the CX-93 pressure wave supercharger. The simulation was conducted using a CFD code for unsteady 3D k-e, k-co model approach to reproduce data such as pressures, temperature and mass flows which are usually measured in real engine pressure wave supercharging. The computational domain for uRANS was modeled as a moving rotational domain with adaptive meshing. Results such as velocity, pressure and temperature field in the rotor channels were obtained for exhaust gas inlet pressure of 0.28 MPa and 1465 K temperature at different rotational speeds. The air inlet state considered was: 0,098 MPa and 293 K. Supercharging by means of a pressure wave supercharger, in order to improve the performance of an internal combustion engine, appears to be a promising solution since the exhaust gas generates a benefice boost of intake air with significant advantages when compared to the conventional turbocharging. The numerical modelling of the complex phenomena occurring within the narrow channels might be a useful tool for improving the pressure exchange between the working fluids, either by modifying the input parameters or by optimizing the geometry of the rotor, ports or pockets.

Numerical study on the interaction characterization of rotating detonation wave and turbine rotor blades

Rotating detonation as a kind of pressure gain combustion is expected to greatly improve efficiency when applied to gas turbine engines. In this paper, the operation of rotating detonation combustor and turbine rotor blade was studied. Firstly, the analysis of the interaction between detonation wave and turbine blade shows that the compression of gas by detonation wave and reflected wave will lead to a sharp increase in the temperature at the wall of blade. When the detonation wave propagates, the oscillation amplitudes of pressure and temperature at the turbine inlet are 70% and 75% respectively, and the detonation oblique shock will change the flow trajectory of the air flow, resulting in the flow direction deviating from the incident angle. Then the comparison between detonation and deflagration shows that the total pressure of detonation is higher and will have greater work potential. The torque generated by the blades under detonation has the characteristics of high-frequency oscillation, which may be detrimental to the operation of the engine.

Feasibility of Boosting Low-Energy-Quality Steam by Using Wave Rotor

Owing to the difficult utilization of the low-pressure level in the process industry, the low-energy-quality steam is often condensed to recover the demineralized water or just discharged directly, causing a huge waste of thermal energy. A novel technology of enhancing the steam’s energy quality by using the wave rotor based on the principle of moving shockwave compression is proposed. The supercharging ability of 3-port wave rotor is studied by meaning of 1-dimension unsteady theory and computational fluid dynamic. A practical thermodynamic flowsheet of boosting the low-pressure steam driven by high-pressure steam is also proposed and analysed in detail. As an example, to boost the saturated steam of pressure 1.0 MPa to 1.953 MPa, a three-stage wave rotor solution is proposed and is verified its feasibility. The high supercharging ratio and entrainment ratio of the wave rotor are much higher than the traditional steam ejector shows the feasibility of enhancing energy-quality of low-pressure steam.

Performance Analysis of Wave Rotor Based on Response Surface Optimization Method

AbstractAn optimized wave rotor refrigerator (WRR) that can convert part of the expansion work into shaft work to improve the refrigeration performance is obtained by the optimization method. Bézier curve is used to establish a two-dimensional simplified model, and response surface method and Non-linear Programming by Quadratic Lagrange (NLPQL) optimization algorithm are used to search for the optimal wave rotor structure. The results show that the optimized wave rotor shape is rear-back bending. Compared with the original rotor, the isentropic expansion efficiency of the optimized rotor is higher under different pressure ratios and relative velocity, and changes more gently under different pressure ratios. Moreover, the expansion power of the optimized rotor is mainly converted into shaft power, while the pressure energy and thermal energy increase at the hot end are relatively small. The pressure fluctuations on the inlet and outlet sides of the optimized rotor are smoother, and the compression waves that are constantly reflected during the low-temperature exhaust stage have a smaller intensity, which helps to improve the performance of WRR. The optimized rotor can significantly reduce the entropy production in the refrigeration process, especially the entropy production by velocity gradients. When the pressure ratio is 2.0 and relative velocity is 23 m/s, the isentropic expansion efficiency increases from 56.8% of the original rotor to 62.08% of the optimized rotor.

Investigation of pressure wave behaviors in the rotational speed effects on a pressure-exchange wave rotor

A wave rotor is suitable for compact and efficient pressure-exchange between gas flows. This work measured the circumferential pressure distribution of the rotor/stator interfaces and utilized a CFD method to simulate the unsteady pressure waves. The experimental and CFD results showed some slopes in the circumferential pressure distributions, and the slopes indicated the traces of specific unsteady pressure waves. Such traces varied regularly if the rotational speed varied within a range from −11% to +11% off the baseline value, but they were seriously disturbed if the rotational speed varied by −45% from the baseline value. It verified that a pressure wave in a wave rotor tended to keep its pressure ratio and propagation velocity unchanged if the rotational speed varied by a small extent, and that the pressure wave could not keep its propagation patterns if the rotational speed varied by a large extent. Because of the pressure wave behaviors, the wave rotor demonstrated specific regulations of the rotational speed effects on its operational states.

Gas turbine performance enhancement for naval ship propulsion using wave rotors

The propulsion demands of high-speed naval vessels often rely on gas turbines, producing significant amount of power achieving thus high performance requirements. Gas turbines can be used either to provide purely mechanical propulsion, or alternatively to generate electricity, which is subsequently used by electric drives to propel the ship. However, the thermal efficiencies of gas turbines are lower than those of Diesel engines of similar power. In the context of improving the performance of existing marine gas turbines, it is proposed to enhance engine’s performance by integrating a pressure wave supercharger (or wave rotor), while keeping the basic components of the baseline engine unchanged. This article is an application of a method developed by the author for marine gas turbines with and without recuperator, [Fatsis 2019]. It is found that important benefits are obtained for the topped engines in comparison to the self-standing baseline engines. The wave rotor integration is more appropriate for engines with low compression ratios and high turbine inlet temperatures. Application of wave rotor technology to recuperated marine gas turbines shows efficiency gain exceeding 19% for all the compression ratio and turbine inlet temperatures examined. Abbreviations: COGAS, Combined gas turbine and steam turbine; COGES, Combined gas turbine electric and steam; GTE, Gas turbine engines