Numerical investigation of transitions in flow states and variation in aerodynamic forces for flow around square cylinders arranged inline

This study focuses on the transitions in flow states around two-, three- and four-inline square cylinders under the effect of Reynolds numbers at two different gap spacing values using the lattice Boltzmann method. For this purpose, Reynolds number is varied in the range 1–130 while two different values of spacing taken into account are gap spacing?=?2 and 5. Before going to actual problem, the code is tested for flow around a single square cylinder by comparing the results with experimental and numerical results of other researchers, and good agreement is found. The current numerical computations yield that for both spacing values and all combinations of cylinders there exist three different sates of flow depending on Reynolds numbers: steady state, transitional state and unsteady state. It is found that the range of Reynolds numbers for these flow states is different for both spacing values. At gap spacing?=?2 the range of Reynolds numbers for each flow state decreases by increasing the number of cylinders while at gap spacing?=?5 opposite trend is observed. The results also show that at gap spacing?=?2 the reduction in drag force is greater than the corresponding reduction at gap spacing?=?5. The maximum reduction in drag force is observed at Reynolds numbers?=?1 at both spacing values. Similarly, at both spacing values and all Reynolds numbers, the maximum reduction in drag force is observed for the case of four-inline square cylinders.     

Prediction of Group Delay Distribution Around Receiving Point Using Modified IRI Model and IGRF Model

The international reference ionosphere (IRI) model is generally accepted standard ionosphere model. It describes the ionosphere environment in quiet state and predicts the ionosphere parameters within a certain precision. In this paper, we have made a breakthrough in the application of the IRI model by modifying the model for regions of China. The main objectives of this modification are to construct the ionosphere parameters foF2 and M (3000) F2 by using the Chinese reference ionosphere (CRI) coefficients, appropriately increase hmE and hmF2 height, reduce the thickness of F layer, validate the parameter by the measured values, and solve the electron concentration distribution with quasi-parabolic segment (QPS). In this paper, 3D ray tracing algorithm is constructed based on the modified IRI model and international geomagnetic reference field (IGRF) model. In short-wave propagation, it can be used to predict the electromagnetic parameters of the receiving point, such as the receiving area, maximum useable frequency (MUF) and the distribution of the group delay etc., which can help to determine the suitability of the communication. As an example, we estimate the group delay distributions around Changchun in the detection from Qingdao to Changchun using the modified IRI model and IGRF model, and provide technical support for the short-wave communication between the two cities.