In this paper, a study of the high-speed gas jet of a rocket nozzle underwater was carried out using commercially available CFD software FLUENT with it’s user-defined-function. The volume of fluid technique based on ...In this paper, a study of the high-speed gas jet of a rocket nozzle underwater was carried out using commercially available CFD software FLUENT with it’s user-defined-function. The volume of fluid technique based on finite volume method was adopted to solve the time-dependent multiphase flow including a compressible phase, and the PISO algorithm was included. The computed results show that this problem was calculated successfully. The gas bubble behind the nozzle, and the wave structure existing in highly compressed gas in water were captured accurately.展开更多
ANSYS FLUENT提供的焦炭燃烧模型中,忽略了碳粒燃烧过程中灰层累积的影响,导致模拟焦炭燃烧速率偏大。为此,基于FLUENT原始模型,结合碳粒燃烧过程中灰层积累对燃烧的抑制原理,利用FLUENT中User Defined Functions(UDF)模块,提出一种基...ANSYS FLUENT提供的焦炭燃烧模型中,忽略了碳粒燃烧过程中灰层累积的影响,导致模拟焦炭燃烧速率偏大。为此,基于FLUENT原始模型,结合碳粒燃烧过程中灰层积累对燃烧的抑制原理,利用FLUENT中User Defined Functions(UDF)模块,提出一种基于灰层累积的焦炭燃烧缩核数学模型,称为"基于灰层累积的动力/扩散控制"燃烧模型。计算结果表明:相比于原始模型,改进模型中炉膛速度与温度分布更符合热力计算值;模拟得到的飞灰含碳量与实际测值基本一致,说明改进模型更加合理,且模拟结果相对准确。展开更多
This research work is focused on simulation of laser assisted turning as a new solution for machining of hard steels. A transient, three-dimensional model was developed to predict the temperature distribution of a rot...This research work is focused on simulation of laser assisted turning as a new solution for machining of hard steels. A transient, three-dimensional model was developed to predict the temperature distribution of a rotated cylindrical steel workpiece subjected to a localized heating using a moving Gaussian laser beam. In this regard, a User-Defined Function was created to overcome the problem of a moving Gaussian heat source’ definition. This User-Defined Function was compiled into a finite volume software package (Fluent), where three-dimensional single precision solver was used for analysis. Based on this model, simulation of the surface temperature of 32 mm diameter workpiece of AISI51 50H steel was performed as a function of time at a specific distance behind the laser beam spot, which is corresponding to 30° angle from the laser beam. The simulation results were compared with other published data of the same steel type where a close agreement was obtained. The verified model was used for simulation of laser assisted turning of 20 mm diameter workpiece of AISI D2 tool steel. The cutting depth, behind the laser beam, was set at a distance corresponding to 60° angle from the laser beam for having sufficient access for handling both laser head and cutting tool. This cutting depth was studied as a function of different lasers and machining parameters. The results indicated that the optimum parameters for successful laser-assisted turning process of the concerned steels are 800 W laser power, 5 mm laser beam spot diameter, 20 sec preheating time, 0.8 mm/sec laser scanning speed, 300 rpm rotational speed and 0.8 mm/sec feed rate. These parameters ensure easy/successful cutting of 1 mm depth in one pass without deteriorating the properties of the remaining bulk material. It can be deduced that the developed model might provide a useful tool for online process control of different steel types regardless of their physical properties and geometries.展开更多
文摘In this paper, a study of the high-speed gas jet of a rocket nozzle underwater was carried out using commercially available CFD software FLUENT with it’s user-defined-function. The volume of fluid technique based on finite volume method was adopted to solve the time-dependent multiphase flow including a compressible phase, and the PISO algorithm was included. The computed results show that this problem was calculated successfully. The gas bubble behind the nozzle, and the wave structure existing in highly compressed gas in water were captured accurately.
文摘ANSYS FLUENT提供的焦炭燃烧模型中,忽略了碳粒燃烧过程中灰层累积的影响,导致模拟焦炭燃烧速率偏大。为此,基于FLUENT原始模型,结合碳粒燃烧过程中灰层积累对燃烧的抑制原理,利用FLUENT中User Defined Functions(UDF)模块,提出一种基于灰层累积的焦炭燃烧缩核数学模型,称为"基于灰层累积的动力/扩散控制"燃烧模型。计算结果表明:相比于原始模型,改进模型中炉膛速度与温度分布更符合热力计算值;模拟得到的飞灰含碳量与实际测值基本一致,说明改进模型更加合理,且模拟结果相对准确。
文摘This research work is focused on simulation of laser assisted turning as a new solution for machining of hard steels. A transient, three-dimensional model was developed to predict the temperature distribution of a rotated cylindrical steel workpiece subjected to a localized heating using a moving Gaussian laser beam. In this regard, a User-Defined Function was created to overcome the problem of a moving Gaussian heat source’ definition. This User-Defined Function was compiled into a finite volume software package (Fluent), where three-dimensional single precision solver was used for analysis. Based on this model, simulation of the surface temperature of 32 mm diameter workpiece of AISI51 50H steel was performed as a function of time at a specific distance behind the laser beam spot, which is corresponding to 30° angle from the laser beam. The simulation results were compared with other published data of the same steel type where a close agreement was obtained. The verified model was used for simulation of laser assisted turning of 20 mm diameter workpiece of AISI D2 tool steel. The cutting depth, behind the laser beam, was set at a distance corresponding to 60° angle from the laser beam for having sufficient access for handling both laser head and cutting tool. This cutting depth was studied as a function of different lasers and machining parameters. The results indicated that the optimum parameters for successful laser-assisted turning process of the concerned steels are 800 W laser power, 5 mm laser beam spot diameter, 20 sec preheating time, 0.8 mm/sec laser scanning speed, 300 rpm rotational speed and 0.8 mm/sec feed rate. These parameters ensure easy/successful cutting of 1 mm depth in one pass without deteriorating the properties of the remaining bulk material. It can be deduced that the developed model might provide a useful tool for online process control of different steel types regardless of their physical properties and geometries.
