Papers by Keyword: Pressure Fluctuation

Abstract: Underwater exercise programs are among the nursing programs for which positive effects have been reported with regard to the promotion of good health in diverse subjects, such as patients suffering arthritis, as well as elderly people and middle-aged women. Through many previously conducted studies, subjects participating in underwater exercises have been reported to continuously experience reduced pain, and improvement in muscle strength, flexibility, sense of balance, and muscular endurance. However, few studies have delved into the fundamental phenomena of positive effects of underwater exercises on the human body. In this study, a model of the upper limbs of the human body was used in a simulation of underwater exercises to analyse the resulting pressure fluctuation on the skin of the hands and arms of the model through the methods of computational fluid dynamics. During the simulation of underwater exercises, pressure fluctuation of diverse frequencies, arising from the vortex flow around the articulations of the fingers and hands of the model, were identified and were seen to create varied cutaneous stimulations and massage effects. Such cutaneous stimulations seem to continuously excite capillary vessels situated between hands and finger joints, creating positive effects in blood circulation around pain sites of patients suffering from arthritis.

Abstract: When trains with high speed pass through the tunnel, there is pressure fluctuation in the tunnel which will cause discomfort of the driver and the passengers. Using unsteady one dimensional flow model, the aerodynamic effect caused by the train with speed of 120km/s running through the tunnel was calculated and analyzed. The results show that the routine tunnel size of Ф5.5m for metro lines can not meet the standard for comfort level. Instead, tunnels with inner diameters of 6.8m and 10.36m were recommended.

Abstract: In order to investigate the characteristics of solid attitude control system (SACS) using proportional pintle thrusters, an ACS comprised of dual collaborative thrusters was designed and studied by theory and cold-flow test. Experiments were conducted to ascertain thrust variation at different pintle locations. With the purpose of studying thrust control principle, the thrust, chamber pressure and pintle displacement of two thrusters were measured, which worked differentially in the process. Results show that a nearly linear relationship is found between the thrust and valve pintle position and the two thrusters can work synchronous to produce a resultant force, whose direction and value can vary continuously. Besides, collaborative work mode of dual thrusters is conducive to the stabilization of chamber pressure which is beneficial to the choice of propellant.

Abstract: This paper presents the analysis on the periodic fluctuation of pressure in flue and air system of a 660MW supercritical boiler, firing high sulfur coal. The analysis shows that the fluctuation is resulted from a blockage in its air pre-heater, especially in winter. Just as the temperature of flue gas lower than its acid dew point, corrosion occurs and induces the blockage furthermore. This paper exhibits a typical case in boiler firing high sulfur coal.

Abstract: Human comfort is of great importance to main powerhouse and vibration level should be controlled below the human comfort limit. Comparison of ISO2631/1-1985 and ISO2631/1-1997 was performed firstly in this study. It points out that weighted root-mean-square acceleration is basic variable for vibration evaluation. The reduced comfort boundary of 2 hours (0.260m/s²) in 1985 version is very close to the comfort threshold (0.315m/s²) in 1997 version. Above two values were selected as human comfort standard in this paper. After that, 3D dynamic finite element model of HongPing pumped storage station was established and vibration analysis under pressure fluctuations was conducted using time history method. The calculation results indicated that vibration of generator floor was mainly caused by the multiples of runner blade number frequency. Vibration level of generator floor would not lead to human discomfort.

Abstract: The medium flow of control valve is a typical complex unsteady flow, the internal flow is very unstable which leads to trim or body with vibration of different amplitude, therefore, control valve has been a failure-prone components in the turbine inlet steam system. This paper take the new valve as the research object, by computational fluid dynamics (CFD) software, the numerical simulation of the internal steam steady state flow field of valve normal work a typical opening in the process of opening is made, and obtain the internal flow field visualization distribution and flow characteristics of control valve. Extract unstable place pressure pulsation of the flow field, get the pulse frequency, and provide the basis for the design, optimization and application of low vibration noise control valve.

Abstract: The unsteady pressure fluctuation is one of the major factors affecting the operational stability of a fire turbopump. Based on the experimental operation conditions of the turbopump, the inner unsteady flow field in the turbopump is simulated by computational fluid dynamics (CFD), and the pressure fluctuations at the zones near the turbine suction chamber, the turbine impeller inlet, the turbine outlet and the interface of pump impeller/volute are investigated by time-frequency analysis methods. The results show that high pressure fluctuation can be observed near the interface of turbine impeller-guide vane and the interface of pump impeller–volute caused by rotor-stator interaction (RSI). Moreover, turbine pressure fluctuation frequencies are identified as the 14 times and 26 times of rotating frequency and the fluctuant amplitude depends on the guide vane inlet angle; whereas, pump pressure fluctuation frequencies are observed at the times of the blade passing frequency (BPF), while the frequencies higher than 10 times of BPF have less effect on the pump vibrations. The results of unsteady pressure pulsation could be used to guide the optimum design of the fire turbopump, which is in favor of obtaining more stable performance of the turbopump.

Abstract: Rotor/Stator interaction in axial-flow pump is the main reason for pressure fluctuates, which impacts on operating security of axial flow pump. In order to study Rotor/Stator interaction phenomenon in axial flow pump, TJ04-ZL-02 hydraulic axial flow pump model is investigated under different operating condition by unsteady simulation based on k-ω turbulence model. Numerical results show that: different flow operating conditions will lead to different Rotor/Stator interaction phenomenon, and also different pressure fluctuation. Fluctuation amplitude in design operating condition is smaller than off design operating condition. So the study proves that pump running in the design operating conditions has important beneficial to the pump operational stability.

Abstract: This paper is based on the wavelet transform theory and the Hilbert transform, it aims at researching on the pressure fluctuation characteristics in the bed, through analyzing and comparing the calculated envelope spectrum of pressure signal after transforms. On the basis of self-built cold fluidized bed, we choose to change the air flow and diameter of particle in fluidized bed as the two influencing factors. For researching the pressure fluctuation characteristics of fluidized bed, we collect pressure signal of the large particle fluidized bed which under normal operation conditions. The experimental results reveal that: as the increasing of the air flow, the energy of pressure increases; and with the increase of particle size in fluidized bed, the pressure fluctuation decreases in the bed.

Abstract: Numerical simulation of unsteady flow and flow-induced sound of an airfoil and a wing/plate junction are performed in the paper by large eddy simulation (LES) and FW-H acoustic analogy. The vortical flows around a NACA0015 airfoil at two angles of attack (0°and 8°) are simulated and analyzed by vortex identification. Simultaneously, the wall pressure fluctuations of the airfoil are computed. At two angles of attack, the flow induced sound of the airfoil is predicted. The computed power spectra agree well with experimental measurements. So the capability of large eddy simulation in predicting unsteady flow and flow induced sound is validated. Subsequently, the horse-shoe vortex around a wing/plate junction in water is computed. Furthermore, the calculations of wall pressure fluctuations and flow induced sound of the junction model at three velocities are accomplished. The predicted results are compared favorably with measured data in large circulation water channel. So the numerical approach for flow induced sound of wing/plate junction in water is validated. It shows that the numerical simulation method in the paper is credible.