Flows In Industrial Applications Research Articles

Optimization of hot-wire thermal flow sensor based on a neural net model

In this paper, we apply an optimization technique that inverts the function of a novel thermal flow sensor. The nominal output of the present sensor is the increase in wire temperature and this output is a function of the time constant of the heated wire and thus also of the velocity of flow. At very low flow velocities, the response is determined almost entirely by the time constant of the wire while at high velocities the device acts almost like a constant current hot-wire anemometer. The present thermal flow sensor, which can be used over a large range of velocities, is well suited for measurements of steady or slowly varying unsteady flows in industrial applications. The calibration data of the sensor consists of a set of curves at different fluid temperatures. Each curve represents the output voltage of the sensor as a function of the flow velocity. An artificial neural net model that approximates the calibration data for the sensor has been trained and it has good accuracy. Based on the neural net model, the optimization algorithm determines the flow velocity of the flowing gas in a pipe if the thermal flow sensor voltage measurement and fluid temperature are known. The problem reduces to minimizing a positive cost function that measures the difference between the neural net approximated voltage and its desired value. The simulation results demonstrate the effectiveness of the algorithm.

Statistical Mechanics of Turbulent Flows

Statistical Mechanics of Turbulent Flows

96/06425 Direct and large-eddy simulation of turbulent fluid flow using the lattice-Boltzmann scheme

Abstract This paper reports on direct and large-eddy simulations (LES) of turbulent flows using the lattice-Boltzmann scheme for the discretization of the Navier-Stokes equations. It is divided into two parts. The first part deals with direct simulation of fully developed turbulent channel flow with heat transfer in order to check the performance of our solver. It is shown that the present numerical results agree well with the numerical results reported by Kim et al. (1987). The second part deals with large-eddy simulation (LES) of the turbulent flow in a baffled stirred tank reactor. This kind of equipment is frequently used in the (petro)chemical industry for mixing applications and is, therefore, of direct practical relevance. Large-eddy simulation is a powerful tool to study such flows, as it accounts in a natural way for the unsteady and quasi-periodic behavior of these flows. The results of our first attempt to simulate this flow by means of modeling the impact of the mechanical impeller on the flow field via a varying force field in space and time, reveal a fair agreement with available experimental data. In accordance with measurements, it is shown that the thickness of the impeller blades plays an important role for the motion of the fluid in the vicinity of the impeller. In conclusion, the present application of LES to this engineering flow problem clearly shows the potential of LES as a tool to investigate turbulent flows in industrial applications of practical importance.

Direct and large-eddy simulation of turbulent fluid flow using the lattice-Boltzmann scheme

This paper reports on direct and large-eddy simulations (LES) of turbulent flows using the lattice-Boltzmann scheme for the discretization of the Navier-Stokes equations. It is divided into two parts. The first part deals with direct simulation of fully developed turbulent channel flow with heat transfer in order to check the performance of our solver. It is shown that the present numerical results agree well with the numerical results reported by Kim et al. (1987). The second part deals with large-eddy simulation (LES) of the turbulent flow in a baffled stirred tank reactor. This kind of equipment is frequently used in the (petro)chemical industry for mixing applications and is, therefore, of direct practical relevance. Large-eddy simulation is a powerful tool to study such flows, as it accounts in a natural way for the unsteady and quasi-periodic behavior of these flows. The results of our first attempt to simulate this flow by means of modeling the impact of the mechanical impeller on the flow field via a varying force field in space and time, reveal a fair agreement with available experimental data. In accordance with measurements, it is shown that the thickness of the impeller blades plays an important role for the motion of the fluid in the vicinity of the impeller. In conclusion, the present application of LES to this engineering flow problem clearly shows the potential of LES as a tool to investigate turbulent flows in industrial applications of practical importance.

128 高解像度フィルムスキャナを用いたPIV計測

PIV technique has been established as a useful technique of velocity field measurements of fluid flows in industrial applications as well as in fundamental researches on fluid dynamics. However, there are some practical problems to apply PIV technique. These are the know-how of tracer-particle-seeding and illumination, the selection of image processing algorithm to obtain velocity vector, the cost of system, and so on. This paper describes a practical PIV system combining high-resolution film scanner and simple digital-image-processing technique, and its applications. The results obtained are compared with ones obtained by conservative technique with optical Fourier transformation.