浅谈小型连铸浊环水系统的稳压问题

连铸技术已在我国得到普遍推广应用,而对连铸生产过程起至关重要作用的循环给水系统特别是浊环水系统的给水压力波动严重,给连铸的生产带来诸多不利因素,本文结合长钢小型方坯连铸的设计及生产运行经验,提出了浊环水系统的各种稳压措施。

Stall Characteristics and Tip Clearance Effects in Forward Swept Axial Compressor Rotors

Tilting the blade sections to the flow direction （blade sweep） would increase the operating range of an axial compressor due to modifications in the pressure and velocity fields on the suction surface. On the other hand, blade tip gap, though finite, has great influence on the performance of a turbomachine. The present paper investigates the combined effect of these two factors on various flow characteristics iu＇a low speed axial flow compressor. For this present study, nine computational domains were modeled; three rotor sweep configurations （0°, 20° and 30°）and for three different clearance levels for each rotor. Commercial CFD solver ANSYS CFX 11.0 is used for the simulations. Results indicated that tip chordline sweep is found to improve the stall margin of the compressor by modifying the suction surface boundary layer migration phenomenon. Diffusion Factor （DF） contours showed the severity of stalling with unswept rotor. For the swept rotors, the zones of high probable stall are less severe and they become less in size with increasing sweep. Increment in the tip gap is found to gradually affect the performance of unswept rotor, while the effect is very high for the two swept rotors for the earlier increments. As a minimum clearance is unavoidable, swept rotors suffer relatively higher deviation from the idealistic behavior than the unswept rotor due to tip clearance.

On the stability of contact discontinuity for Cauchy problem of compress Navier-Stokes equations with general initial data

Abstract In this paper, we study the stability of solutions of the Cauchy problem for 1-D compressible Narvier- Stokes equations with general initial data. The asymptotic limit of solution is found, under some conditions. The results in this paper imply the case that the limit function of solution as t → ee is a viscous contact wave in the sense, which approximates the contact discontinuity on any finite-time interval as the heat conduction coefficients toward zero. As a by-product, the decay rates of the solution for the fast diffusion equations are also obtained. The proofs are based on the elementary energy method and the study of asymptotic behavior of the solution to the fast diffusion equation.

Dynamic analysis on pressure fluctuation in vaneless region of a pump turbine

As the pump turbine tends to be operated with high head and high rotational speed, the study of stability problems becomes more important. The pump turbine usually works at operating conditions where the guide vanes experience strong vibrations. However, most traditional studies were carried out based on constant GVO(guide vane opening) simulations. In this work, dynamic analysis on pressure fluctuation in the vaneless region of a pump turbine model was conducted using a dynamic mesh method in turbine mode. 3D unsteady simulations were conducted where GVO was closed and opened by 1° from the initial 18°. Detailed time domain and frequency domain characteristics on pressure fluctuation in the vaneless region under different guide vane rotational states compared with constant GVO simulations were investigated. Results show that, during the guide vanes oscillating process, the low and intermediate frequency components in the vaneless region are significantly different. The amplitudes of pressure fluctuation are higher than those with constant GVO simulations, which agree better with the experimental data. In addition, the pressure fluctuation increases when GVO is opened, and vice versa. It can be concluded that pressure fluctuation in the vaneless region is strongly influenced by the oscillating of the guide vanes.

Investigation of the spike-stall warning method using the blade passing signal

The vaned-diffuser usually brings compressor instability problems under the small flow rate, for instance the spike-type rotating stall phenomenon which restricts the operation range and may cause the trouble of blade fatigue. Since it is difficult to mathematically predict the spike-type stall for its randomness, finding out a practical method to warning this stall precursor appears to be meaningful. The paper explains the relationship between the spike-type precursor and the blade passing irregularity coefficient to analyze whether this coefficient is appropriate for the spike-stall warning inside a centrifugal compressor with the vaned-diffuser. The advanced wireless measurements were conducted on a 1.5 stages test centrifugal compressor to capture the unsteady behavior progressing from the design to stall inception within the region between the impeller trailing edge(TE) and diffuser leading edge(LE). The circumferential distribution of the blade passing irregularity has been quantitatively revealed.The steep increase of the blade passing irregularity at some "special locations", which is responsible for the onset of the spiketype precursor, is highlighted. Also, to further understand the spike precursor inside the diffuser passage corresponding to the circumferential "special location" with maximum irregularity, the high-response transient measurement within this passage is presented. With the help of full-annulus computational fluid dynamics(CFD) simulation and the mathematical model, it is proved that the blade passing irregularity precisely reflects the flow characteristics during the spike precursor, which presents the guidance for this stall warning method.

Global existence and stability of a stationary Mach reflection

We prove the global existence and stability of a wave structure containing a stationary Mach con- figuration, which occurs when an incident shock front hits a wall with a large incident angle. Our result shows that tile data of the upstream flow and the pressure at downstream part jointly determine the whole flow, as well a the wave structure. Particularly, we show that the height of the Mach stem depends not only on the data of upstream flow, but also on the pressure at downstream flow. The flow with the assigned wave structure is governed by a free boundary value problem for the Euler system. In the problem the location of the triple point, the shock fronts and the contact discontinuity are all unknown, they are finally determined together with the solution.

EXISTENCE AND UNIQUENESS OF A SOLUTION TO AN AEROACOUSTIC MODEL

A linear modelling of aeroacoustic waves propagation is discussed. The first point is an existence and uniqueness, theorem. But restrictive assumptions are required on the velocity of the flow. Then a counter example proves that they are necessary.