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The detection chamber is an important part of the bionic olfactory detection analysis instrument. Unreasonable structure design of detection chamber can cause gas vortex and prolong the sensors' response and recovery time. Non-uniform distribution of airflow field can cause inconsistence of the sensor array in numerical induction. Therefore, it is significant to explore the characteristics of gas flow and distribution, optimize the flow field structure, improve the uniformity and stability of the flow rate and advance the accuracy and repeatability of olfactory detection chamber. However, the traditional method of further manufacture design improvements requires long transformation time, and high costs, and the measurement range is usually disappointing. Computational Fluid Dynamics (CFD) can provide detailed information on airflow simulation and ensure convenient design of agricultural equipments. In order to optimize the structure of bionic olfactory detection chamber of sweeping type, and improve the uniformity and stability of fluid velocity distribution, based on the differential equations of fluid motion, the internal flow field of olfactory detection chamber was numerically simulated by using the CFD. This paper proposed the models of 3 types of chamber detection original structures, and the uniformity and stability of olfactory sensors' detection area from the optimal model were compared with the test results. The 3 types of detection chamber original structures were linear arrangement, parallel arrangement and structure of multi nasal ducts. Each model design was mainly composed of an intake pipe, a detection chamber, a sensor array and a vent pipe. The fluid flow rate was much smaller than the acoustic velocity and the fluid flow was considered as an incompressible process inside the chamber. In the process of olfactory detection, the fluid flowed into the detection chamber from the intake pipe and flowed out of the vent pipe, so the inlet boundary was set to velocity inlet. Outlet pressure boundary conditions were selected, and the natural pressure was taken as the boundary value. The fluid temperature in the chamber was room temperature which was 26 ℃. The wall had no slip boundary condition, and was assumed to be a rigid wall without considering the influence of wall elasticity. The speed deviation ratio and the nonuniformity coefficient were chosen as comprehensive evaluation indicators. The velocity distribution in chamber flow field was obtained and used to analyze the original structures to provide the preference design. The detection chamber of multi nasal ducts corresponded to inclination model. The simulation results indicated that the structures of detection chamber influenced air velocity distribution. The detection chamber of multi nasal ducts along the pipe axis (0.035-0.049 m range) had a velocity smooth region, the velocity of which was stabilized merely at 0.018-0.268 m/s, which could meet the requirement of detection condition. There were no velocity smooth regions in the linear arrangement, and the airflow velocity of smooth regions in parallel arrangement merely ranged from 0.001 to 0.018 m/s. The detection chamber of multi nasal ducts showed the advantage in the uniform and stability of velocity, of which the maximum values of speed deviation ratio and nonuniformity coefficient were calculated to be 0.830 6 and 0.292, respectively. Meanwhile, in the gas detection period by the numerical simulation, the detection time of 3 models was 223.4, 302.0 and 213.8 s, respectively, and the minimum value of the structure of multi nasal ducts showed that it had fast flow response and high working efficiency. Moreover, the optimum structure could effectively improve the consistency of the sensors' numerical detection, and the standard deviation and the coefficient of variation ranged from 0.153 5 to 0.428 3 and from 0.030 5 to 0.082 7, respectively. The results provide a reference for the uniformity design of flow field structures similar to the detection chamber. [ABSTRACT FROM AUTHOR]

The paper presents a methodology for calculating the unsteady aerodynamic forces characteristics and gust response of the unmanned air vehicle (UAV) model using computational fluid dynamics (CFD) tools, and the efficiency of gust alleviation based on direct force control are also studied. Based on unsteady Euler equations, dynamic responses in vertical gust flow perturbation are investigated. The grid velocity method, which is used to model unsteady flow via grid movement, is introduced to simulate the gust influence. This approach avoids numerical instabilities and decouples the step change in the angle of attack from a pitch rate. And the dynamic chimera grid method is used to simulate the rudder movement of the gust alleviation effect. Numerical results for the NACA0006 airfoil are validated by comparison with analytical results for two dimensional indicial responses. The initial and final lift values of the indicial responses closely match the exact analytical values as given by piston theory and quasi steady thin airfoil theory respectively. The solutions at small times match quite closely the exact solution which is known only for small times given by linear theory. The application of the same method to the UAV model reveals important characteristics of the three-dimensional vertical discrete gust response for the One-minus-cosine gust profile and gusts cause step changes in the angle of attack, and important characteristics of the gust response and resulting flow features are explained. Furthermore, the flow perturbations under dynamic rudder motion are investigated using moving chimera grid technique. Our study shows that with certain designed motions, the flapping rudder can effectively alleviate the freestream gust fluctuation and ensure a stable flight. However, no single parameter can determine whether the flapping rudder can reduce the gust effect. Finally, unsteady aerodynamic loads are computed for the wing of model with the designed rudder motion, the significance of the gust propagation effects is shown. It is found that the direct calculation of the gust response using CFD gives quite accurate results and provides a rich database. In general, this paper shows that the well-designed rudder movement can effectively alleviate the freestream gust fluctuation and ensure high flight qualities. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) gradually plays an important role in the evaluation of the wind tunnel design project. This paper is about the evaluation results of the slotted test section of 0.6m x 0.6m continuous transonic wind tunnel including alternative design and flow field quality, especially comparing full slot with half slot. It presents the control equations and boundary conditions for numerical simulation firstly. Then the details of numerical results about the high subsonic and low supersonic flow characteristic are given. The length of velocity uniformity region and velocity deflection angle meet the design accuracy and that proved the rationality. The half slot project was better than the full one at high subsonic. Low supersonic field could be achieved when air was bleed from plenum chamber. However, more bleed air rate, shorter length of velocity uniformity region. Full slot project had less disorder on flow of the plenum chamber than the half. Further investigation on the flow mechanism of re-entry flaps indicated that the flow was unsteady one significantly. [ABSTRACT FROM AUTHOR]

CFD method has the advantage of well simulating the flow over wind farm of complex terrain, compared with the method of using the software WAsP with linear model, thus becoming the development direction of assessment of wind resources in complex terrain. In order to use the CFD package FINE/TURBO and standard k-ε turbulence model with wall function in the wind resources assessment and micrositing of wind farm in the complex terrain, in this paper, Island Nanao had been simulated in wind directions at intervals of 30 degrees, under the assumption of neutral condition, to investigate the influence of inlet condition on the results. The simulation results show that the wind speed-up and intensity don't change essentially under different inlet conditions. Based on this law, with whole year wind data, an assessment method with post processing has been built, providing a strong reference for engineering practice. [ABSTRACT FROM AUTHOR]