| The HVAC (Heating, Ventilation and Air Conditioning) system occupies a large proportion of energy consumption in buildings, which can overly take up about two thirds of the public buildings. Therefore, energy saving of air-conditioning system is the key to building energy conservation, and is of great significance for the construction of environment-friendly society.Real-time monitoring of air volume is the precondition for energy-saving control in air conditioning system, by which the operating status of each device in system can be adjusted to reduce the energy consumption of the air conditioning system effectively. As a new differential pressure flow sensor, the averaging pitot tube is a potential sensor for its real-time monitoring of air volume in the central air conditioning system. But the performance of existing averaging pitot tube can not fully meet the requirements of wind speed measurement of the air conditioning system, especially at a low wind speed condition. Aimed at the problem, this paper carries out a deep research on averaging pitot tube by optimizing its performance on the basis of the averaging pitot tube overview and the principle of bionics.Firstly, this paper establishes a two-dimensional simulation model which is suitable for the averaging pitot tube by analyzing mesh methods and turbulence models Based on the principle of velocity measurement of averaging pitot tube and hydrodynamics theory, the mesh method of block-structured mesh with boundary layer and the unstructured mesh with boundary layer are comparatively studied. And several commonly used turbulence models including Standard k-s model, RNG k-ε model, and SST k-ω model are also investigated carefully. According to the CFD simulation and optimization analysis, a two-dimensional simulation model for the averaging pitot tube is established. And this simulation model is proved to be reliable by comparing the simulation result with the standard parameter of averaging pitot tube.Secondly, this paper proposes a new type of fish-like averaging pitot tube based on the principle of bionics and then carries out optimization design of the structure to make it can be adequate for the low speed measurement of wind. Combined with the law of evolution of the fish in shape to the fluid, a fish-shaped cross-section of averaging pitot tube is proposed And the influence of the shape of the fin-shaped angular and back flow surface on the averaging pitot tube performance are studied by the means of CFD numerical simulation. Overall, the fully comparative analysis and optimization design make the new structure have good measurement performance at the low wind speed condition, which is suitable for the measurement of wind volume in the central air conditioning system.Finally, a platform is established to test the performance of averaging pitot tube in a experimental way. The main component of the experimental platform is averaging pitot tube. And wind generator, standard flowmeter, pressure sensor, temperature, humidity sensor and transparent pipeline are also gathered in the platform. The performance of averaging pitot tube at different levels of wind speed (4-30m/s) is tested, and the data is used to validate the result of numerical simulation in the same condition. Experimental results show that the two-dimensional simulation model this paper proposed is reliable. And the experimental platform can be used for the development of new cross-sectional shape of averaging pitot tube later.The studies of the performance of averaging pitot tube shows that the relative error is 6.48% of CFD numerical simulation using the two-dimensional model compared with standard data, so the numerical model meets the requirements of simulation and can be used to study averaging pitot tube. Meanwhile, the simulation result shows that the measurement performance of the fish-shaped structure of averaging pitot tube decrease 4.96% compared with classical pitot tube, and the performance is also good at the low wind speed condition. |
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