External Characteristic Curve Research Articles

Bifurcation analysis on interaction between ledinegg instability and pressure drop oscillations in a horizontal boiling channel

Abstracts The purpose of this paper is to investigate the instability of pressure drop oscillations and Ledinegg instability associated with considering equipment as a system component. The effect of the pump is taken into account by considering a pressure drop function in terms of mass velocity as the overall head of the system. The system is also modeled with and without the surge tank. The results show that the slope of the external characteristic curve as well as the ratio of the channel length outside the heat section to the length of the heat section and the number of intersections of internal and external characteristic curve, are very effective in the occurrence of Ledinegg instability. Ledinegg instability occurrence depends on the presence of saddle instability in phase portraits of singularities. If there are oscillations, the amplitude of oscillations in this phenomenon is limited. On the other hand, PDO instability results from the interaction of the heated channel with the compressible fluid volume (surge tank). This instability will occur in the negative slope region of the internal characteristic curve provided that the external characteristic curve slope is smaller than the internal one. The amplitude and frequency of the oscillations depend on the deterioration parameter and as it decreases, the oscillations frequency increases. Also the conditions that, both form of Flow excursion instability and limit cycle oscillation will be happen together, has been investigated in this paper.

Performance analysis of single-channel pump with different wrap angles

When a single-channel pump is used to transport living things, the rotating action of the impeller will cause damages to the living things. To improve the survival rate of the single-channel pump for transporting living things and improve the performance, the effect of the impeller wrap angle on the performance of the single-channel pump was studied by numerical simulation. The external characteristic curve is analyzed and the change of the pressure field of the flow field in the flow channel with the wrap angle is grasped. The pressure pulsation at the monitoring points is analyzed, and the influence law of the wrap angle on the performance of the single-channel pump is obtained. This law lays the foundation for subsequent single-channel pump design

Understanding of thermal-hydraulic instabilities and the mutual interactions at supercritical pressure

In the present work, a steady state and a simple transient models are integrated to simulate various thermal-hydraulic (TH) static and dynamic instabilities in a single vertical channel, subjected to time independent power, for supercritical fluid (SCF). The scheme of U.S. supercritical water reactor (SCWR) design is analyzed for different TH instabilities and the mutual interactions of such instabilities. An in-house steady state TH model, which solves a set of nonlinear coupled mass, momentum and energy conservation equations accounting for the pressure and enthalpy dependent thermodynamic equation of state, is implemented to find the solution at the initial equilibrium condition. The steady state model is then validated against the recently available experimental results. Next, the simple transient model is integrated with the steady state model to simulate Ledinegg excursion, pressure drop oscillations (PDOs), density wave oscillations (DWOs), and the mutual interactions of each other in presence as well as in absence of a surge tank at the upstream of the heated section. A number of simulations are carried out considering various typical pump (external) characteristic curves. Results provide the understanding what are the different operational criteria on which the Ledinegg excursion, PDOs and DWOs, or the interactions of the aforementioned TH instabilities will depend.

The study on pressure pulsation of cooling circulating channel of magnetic drive pump

In order to study the layout and developments of pressure pulsation of the main flow passage component in magnetic drive pump, the full flow field numerical research of magnetic drive pump was done with CFX software, the pressure pulsation character of cooling circulating channel and external characteristic curve of pump were obtained. The reliability of the numerical calculation method is verified by the external characteristic test, and the pressure pulsation characteristics in the main flow components of the magnetic drive pump are studied. The results show that the main source of pressure pulsation in magnetic drive pump is the dynamic and static interference between impeller channel, pressurized water chamber and baffle tongue; the main frequency of cooling circulating channel is blade frequency and the pressure fluctuation amplitude of cooling circulation channel decreases with the increase of flow and the propagation of pressure fluctuation in cooling circulation channel weakens the intensity of pressure fluctuating.

Advanced Angle Field Weakening Control Strategy of Permanent Magnet Synchronous Motor

The conventional field weakening algorithm is more dependent on parameters and computational complexity. Therefore, the concept of advanced angle β is introduced, and the conversion of constant torque operation mode to field weakening operation mode is realized by increasing β . In this paper, the conventional field weakening control and advanced angle field weakening are modeled and simulated showing results that the advanced angle field weakening control can make the motor switch smoothly between the constant torque operation mode and the field weakening mode. The dependence of the parameters of the motor is small and the algorithm is simpler. At the same time, the theory of field weakening control of permanent magnet synchronous motor is fused in the vehicle control and the controller is developed. The external characteristic curve of the motor is calibrated by setting up the back-to-back motor test bench. The function of the controller is verified by hardware-in-the-loop experiment. After vehicle verification, it is confirmed that the data can normally enter the field weakening zone to meet the torque response and high-efficiency range. Under the new European driving cycle (NEDC) operating conditions, the efficiency of the whole controller can reach 81.97%.

Study on hump characteristics of pump turbine with different guide vane exit angles

In order to study the influence of different guide vane outlet angles on the external characteristic hump phenomenon under the pump mode of pump turbine with splitter blades, the pump work condition of a pump turbine model pump of a pumped storage generator unit in China was studied. Three different guide vane outlet angle models of 9.6, 17.5 and 25.6 were selected to discuss the variation law of hump characteristics with the guide vane outlet angle under the pump working condition, and the internal flow pattern of the draft tube, impeller and guide vane region was studied. The results show that the calculated external characteristic curves of the three different guide vane exit angles are in good agreement with the test results under the corresponding working conditions. With the increase of the guide vane exit angle, the hump phenomenon becomes more and more obvious and appears earlier, and the smaller the guide vane exit angle is, the higher the head is. There is no wide high efficiency region under the small guide vane exit angle, and the high efficiency region widens as the guide vane exit angle increases. There are secondary flow and backflow in the vane rotating passage, and a large number of whirlpools exist in the guide vane basin. Due to the existence of these bad flow state, the flow loss is greatly increased and the head is reduced, which eventually leads to the hump phenomenon of the external characteristic curve.

Non-linear stability analysis of pressure drop oscillations in a heated channel

A study of non-linear stability analysis using co-dimension two (i.e., two free parameters being varied) bifurcations related to pressure drop oscillations (PDO) in a heated channel has been carried out in this paper. In the existing literature, in the context of PDO, mostly linear stability analysis is done. A few works on non-linear stability analysis are available; however, only co-dimension one bifurcation studies of PDO have been carried out in these works. However, in practice, since the inlet temperature of the coolant is also an independent operating parameter, both inlet temperature, and inlet mass flow rate need to be considered for stability analysis. It is also noted that the existing plethora of studies on PDO is limited to the prediction of supercritical Hopf bifurcation only. However, in the current study, two types of Hopf bifurcations have been identified namely subcritical and supercritical. A subcritical Hopf bifurcation exhibits unstable limit cycles, which is a signature of the existence of unstable solutions for slightly larger perturbations even in the linearly stable region. The existence of unstable solutions indicates that linear stability analysis is not sufficient to identify the overall stability behavior. Also, a generalized Hopf point on the stability boundary has been identified which denotes a boundary between subcritical and supercritical Hopf bifurcation. Furthermore, numerical simulations are carried out in different regions (both stable and unstable) of the parameter space to understand the non-linear phenomena of the system. Moreover, the bifurcations are explained in terms of the interaction of the external and internal characteristic curves of the system. The large and small amplitude cycles are shown in the characteristic curves of the system.

Research on Travel Control System of Hydrostatic Transmission Chassis

Aiming at the control problem of driving system of hydrostatic transmission chassis, the composition of the control system of hydrostatic transmission chassis is introduced and the control method of dual engine is solved. According to the number of driving axles in driving process, The external characteristic curve of the engine controls the variable hydraulic pump by one parameter, controls the rotational speed of the variable hydraulic motor according to the change of the vehicle speed, and introduces the control flow of the brake system. It provides a reference for the design of driving control system of multi-axis hydrostatic transmission chassis.

Entropy production analysis for hump characteristics of a pump turbine model

The hump characteristic is one of the main problems for the stable operation of pump turbines in pump mode. However, traditional methods cannot reflect directly the energy dissipation in the hump region. In this paper, 3D simulations are carried out using the SST k-ω turbulence model in pump mode under different guide vane openings. The numerical results agree with the experimental data. The entropy production theory is introduced to determine the flow losses in the whole passage, based on the numerical simulation. The variation of entropy production under different guide vane openings is presented. The results show that entropy production appears to be a wave, with peaks under different guide vane openings, which correspond to wave troughs in the external characteristic curves. Entropy production mainly happens in the runner, guide vanes and stay vanes for a pump turbine in pump mode. Finally, entropy production rate distribution in the runner, guide vanes and stay vanes is analyzed for four points under the 18 mm guide vane opening in the hump region. The analysis indicates that the losses of the runner and guide vanes lead to hump characteristics. In addition, the losses mainly occur in the runner inlet near the band and on the suction surface of the blades. In the guide vanes and stay vanes, the losses come from pressure surface of the guide vanes and the wake effects of the vanes. A new insight-entropy production analysis is carried out in this paper in order to find the causes of hump characteristics in a pump turbine, and it could provide some basic theoretical guidance for the loss analysis of hydraulic machinery.

Study on the Design Method of Impeller on Low Specific Speed Centrifugal Pump

In this work, the comparative study has been done for five kinds of design methods of the low specific speed centrifugal pump impeller adopted numerical simulation method by software of Fluent, so that the problems can be solved. Many different design methods exists for the low specific speed centrifugal pump impeller, which caused the design effect difficult to control. The numerical simulation method based on the Reynolds time averaged N-S equations (RANS) and RNG κ-ε turbulence models. Results revealed the inner flow pattern of these impeller, and these results were verified by external characteristic experiment. The research results showed that the design method, which adopted compound impeller with short blades and these short blades turned to the suction surface of long blades. Results proved that its flow distribution is even and external characteristic curve is more ideal.

Research on the Establishing Model Method of Engine Eternal Characteristic Curve Based on F Distribution

The external characteristic curve of engine is the basis of choosing engine, matching and optimizing dynamic performance correctly. At present, most models of the external characteristic curve of engine are carried out by using polynomial regression equation for fitting the external characteristic curve of engine. In this paper, an establishing model method of the external characteristic curve of engine based on F distribution testing is proposed. F test with variance analysis is implemented for obtaining the difference of square sum of return difference between the former equation and the latter equation. If the test doesn’t go through, it can rise one level automatically, until the difference about square sum of return difference of the before-after fitting equation is no significant can it stop. This method provides a theoretical criterion for establishing model of the external characteristic curve of engine. When it is applied to the engineering case, the model will have a higher fitting precision.

Method of Determining Vehicle Powertrain Parameter’s Weighting Coefficient Based on Rough Set Theory

In tracked vehicle powertrain integrated designing, rough set theory is applied to determine the parameter’s weighting coefficient on the vehicle 0-32km/h acceleration time. An example of three factors including the shape of engine external characteristic curve, the front gear ratio and shift schedule is given which shows that the method is simple, objective and effective.