Guang-sheng Du

The Transient Aerodynamic Characteristics Around Vans Running Into a Road Tunnel

In this article, the processes of vans running into a one-way two-lane road tunnel are simulated numerically using the dynamic mesh technique and RNG k-ε turbulence model. The transient aerodynamic characteristics around vans are obtained in three cases: a single van, two vans side-by-side and two vans one after another running into the tunnel, respectively. Through a comparison with the results of the wind tunnel experiment, the transient simulation method is verified. The results show that, when a van runs into the tunnel, the aerodynamic drag coefficient increases near the tunnel entrance, and after entering the tunnel, the side force is generated, pointing to the tunnel wall nearer to the van. When two vans run into the tunnel side-by-side, their drag coefficients increase by 50%, and the side force varies sharply with directions changing twice near the tunnel entrance. When two vans run into tunnel one after another, the aerodynamic characteristics around the van in the front is similar to that of a single van, but the aerodynamic forces on the van behind do not have obvious change. Among the three cases, the aerodynamic forces have a sharp change when two vans run side-by-side, so driving side-by-side into a tunnel should be avoided for safety.

THE CALCULATION OF THE PROFILE-LINEAR AVERAGE VELOCITY IN THE TRANSITION REGION FOR ULTRASONIC HEAT METER BASED ON THE METHOD OF LES

The measurement accuracy of an ultrasonic heat meter depends on the relationship of the profile-linear average velocity. There are various methods for the calculation of the laminar and turbulence flow regions, but few methods for the transition region. At present, the traditional method to deal with the transition region is to adopt the relationship for the turbulent flow region. In this article, a simplified model of the pipe is used to study the characteristics of the transition flow with specific Reynolds number. The k - ε model and the Large Eddy Simulation (LES) model are, respectively, used to calculate the flow field of the transition region, and a comparison with the experiment results shows that the LES model is more effective than the k - ε model, it is also shown that there will be a large error if the relationship based on the turbulence flow is used to calculate the profile-linear average velocity relationship of the transition flow. The profile-linear average velocity for the Reynolds number ranging from 5 300 to 10 000 are calculated, and the relationship curve is obtained. The results of this article can be used to improve the measurement accuracy of ultrasonic heat meter and provide a theoretical basis for the research of the whole transition flow.

The influence of installation conditions of heat meters on interior fluid field and flux mearsurement accuracy

Abstract The installation condition of heat meters has an influence on interior fluid field and flux measurement accuracy. In this paper, this influence is investigated through experimental research and numerical simulation. The results indicate that the influence of the length of tubes in front of heat meters can be neglected when L≥4D (L is the length of tubes in front of heat meter, D is the diameter of heat meter). This conclusion has been of great value on academic theory and practical application.

Study of errors in ultrasonic heat meter measurements caused by impurities of water based on ultrasonic attenuation

Impurity is one of the main factors that affect the measurement accuracy of an ultrasonic heat meter. To study the effects of different impurity species and concentrations on the accuracy of heat meters, flow tests were carried out for the suspending of calcium carbonate and yellow mud. By analyzing the attenuation characteristics of the ultrasound amplitude in different impurity concentrations and species, the influence of the impurities on the heat meter measurement accuracy is evaluated. In order to avoid the inaccuracy caused by the sediment of the reflective bottom surface, a vortex generator is put ahead of the reflective surface. According to the test, the calcium carbonate suspension with a mass concentration of 1%, which influences the heat meter accuracy severely, is used as the flow media. The influence of the vortex generator on the calcium carbonate suspension flow field in the heat meter body is studied with numerical simulations. The results of this paper provide some theoretical guide on improving the heat meter measurement accuracy when the water contains impurities.

Experimental and numerical studies of aerodynamic performance of trucks

This article studies the truck-induced airflow. The results of numerical investigations are used to assess the effectiveness of the installed hash symbol (#) shaped fence on the truck. The Reynolds-averaged Navier-Stokes equations are solved using the finite volume method. The computed distributions of the pressure and the air velocity as well as the computed aerodynamic drag coefficients reveal the effects of a fence on the aerodynamic performance of the truck. It is shown that the hash symbol shaped fence plays its role due to its aerodynamic characteristics, better than those of the original model. For various gaps, the optimal position and height of fences are discussed in the article.The experiments in a low speed wind tunnel provide the edidence for validation.

Experimental study of velocity distributions in the transition region of pipes

The accuracy of an ultrasonic flowmeter meaurement depends on the profile-linear average velocity. But this velocity in the transition region is not available at the present. In this article, the velocity in the transition region in pipes is studied by experimental methods. The Particle Image Velocimetry (PIV) is used to measure the flow field in the transition region in pipes, and the measured results from PIV are in good agreement with the Westerwell’s experimental data. Based on the experimental data of PIV, the curves of the profile-linear average velocity in the transition region against the Reynolds number in the range from 2 000 to 20 000 are obtained, and it is shown that the coefficient k is constant when the Reynolds number is in the range of 2 000–2 400 and 6 000–20 000, and the coefficient k is increasing when the Reynolds number is in the range of 2 400–6 000. The results of this article can be used to improve the measurement accuracy of the ultrasonic flowmeters and as a theoretical basis for the research on the transition flow.

THE INFLUENCE OF DIFFERENT DESIGN PARAMETERS AND WORKING CONDITIONS ON CHARACTERISTICS OF HEAT METERS

In this article, the UDF technology in Fluent software is used to simulate three-dimensional flow fields and to obtain various flow parameters. The standard k-ε model and the RNG k-ε model are both used to calculate the inner flow field of the basal meter, and a comparison of the calculated results between two models shows that RNG k-ε model is more effective for calculations of the inner flow of rotary wing mechanism. The influence of tip clearance on the characteristics of the basal meter is studied. The influence of the bottom ribs on the heat meter is evaluated by the numerical simulation method. This article also simulates the flow of disturbance located at the inlet of the basal meter, and shows that a swirl located at the front of the basal meter can affect the stability of the heat meter.

RESREARCH ON FLUID CHARACTERISTIC WITHIN THE ROTATING-WING HEAT METER

In order to improve the performance of rotating-wing heat meter and reduce the cost of development, the three dimensions numerical calculations of the internal fluid characteristic within a heat meter are carried out based on the standard k-ε turbulent mode, the finite volume method and SIMPLE algorithm. The speed field and pressure distribution within heat meter are analyzed according to the result of numerical calculation. The flux measurement accuracy and pressure loss of basal meter are forecasted according to the calculated results. The calculated results of the impeller’s rotating speed are compared with experimental results and prove the validity of the calculated results. This researches shows the calculated results can forecast the performance parameters of basal meter and can provide great help for design of the heat meter.

Numerical study of flow fluctuation attenuation performance of a surge tank

The surge tank plays an important role in ensuring the stability of a water flow standard device. To study the influence of the structure and the working conditions on the regulator performance of a surge tank, a three-dimensional model, including a surge tank, the pipeline and the water tank is built, and the VOF model in the Fluent software is used to simulate the two-phase pulsatile flow in the surge tank. The inlet flow pulsation is defined by the User Defined Functions (UDF), and the outlet flow is set to be a free jet. By calculating the flow fluctuation coefficient of the variation under different flow conditions, the influences of the pulse frequency, the initial water level height and the baffle plate structure on the flow stability are analyzed. It is shown that the surge tank has a good attenuation effect on high-frequency pulsations, there is an optimal initial water level to suppress the fluctuations, the round holes of the baffle should ensure a certain circulation area with the bore diameter small enough to have the necessary damping effect.

The direct numerical simulation of pipe flow

The conservative difference scheme and the third-order Runge-Kutta scheme in combination with the the Crank-Nicholson scheme are used to directly simulate the flow field in a pipe with the Reynolds number of 2 600. The flow field, including the velocity distribution and the turbulence intensity, is obtained by the direct numerical simulation. From the calculated results, the ratio of the linear average velocity along the ultrasonic propagation path to the profile average velocity on the pipe cross-section is also obtained in an ultrasonic flow meter. It is concluded that the direct numerical simulation method can be used to study the ratio of the profile-linear average velocity at low Reynolds number conditions in the transition region and to improve the measurement accuracy of the ultrasonic flow meter.