气体物理

Numerical Simulation of Finite-Rate Catalytic Model Based on ReaxFF-MD

SONG Jiahao, MO Fan, GAO Zhenxun

, Available online , doi: 10.19527/j.cnki.2096-1642.1110

3

0

Abstract:
At present, when CFD method is used to predict surface heat flux, it is generally assumed that the wall condition is full-catalytic wall or non-catalytic wall. Heat flux prediction can be greatly affected by different wall catalytic conditions, and a more reasonable numerical solution can be obtained by using finite-rate catalytic model. However, due to the nonlinear, nonequilibrium, and multiscale characteristics of the catalytic recombination process of high-enthalpy chemical reaction flows on material surfaces, it is extremely difficult to accurately describe the finite-rate catalytic model. In this paper, a finite-rate catalytic model describing the interaction of O and N atoms with SiO₂ surface was constructed by ReaxFFmolecular dynamics method based on the theory and simulation at the microscale. The reentry flow fields of space shuttle orbiter under different catalytic conditions were calculated and compared. The results show that the predicted heat flux of the finite-rate catalytic model agrees well with the flight test data of STS-3 in the altitude range of 70.1 km to 57.8 km, and the model has a certain degree of accuracy.

Numerical Study on Factors Affecting the Storage Tank Performance of an Iodine-ion Thruster

CHEN Mingshi, WANG Xian

, Available online , doi: 10.19527/j.cnki.2096-1642.1097

22

1

Abstract:
Iodine-ion thrusters are mainly used for attitude control and position maintenance of small satellites. They rely on the sublimation and ionization of iodine to generate thrust. The heating methods and structural parameters of the iodine feeding systems have a significant impact on their own working performance. The dynamic grid method was applied to simulate the sublimation phase-transition process of the iodine in the storage tank to study the effects of heating methods and ratios of diameter to height on the performance of storage tank of an iodine-ion thruster. The results indicate that the contact heating method shows the best performance considering the mass flow rate, flow stability, and preheating time among the three heating methods, such as external heating, radiant heating, and contact heating. Besides, the ratio of diameter to height of a storage tank has almost no effect on the change of flow rate for the contact heating method. The flow stability is good. A lower ratio of diameter to height is better for the iodine-ion thruster designed for high thrust. The mass flow rate at the ratio of 0.2 increased by 9.0% compared to the ratio of 1.4. While a larger ratio of diameter to height is better for the iodine-ion thruster designed for high speed of response. The preheating time at the ratio of 0.2 increased by 80% compared to the ratio of 1.4.

Summary and Prospect of Data-Driven Aerothermal Modeling Prediction Methods

WANG Ze, SONG Shufang, WANG Xu, ZHANG Weiwei

, Available online , doi: 10.19527/j.cnki.2096-1642.1068

40

14

Abstract:
The accurate prediction of aerothermal loads is the basis to guide hypersonic vehicle design. Under the back- ground that classical aerothermal prediction methods are more and more difficult to meet the demand of efficient and accurate aerothermal prediction in engineering, data-driven aerothermal modeling prediction methods have gradually become a new paradigm of aerothermal prediction in recent years. Firstly, the relationship between the data-driven aerothermal modeling prediction method and the classical aerothermal prediction method was described. Then, from the modeling idea, the data-driven aerothermal modeling prediction methods were summarized into three categories:The dimensionality reduction modeling method of feature space, pointwise modeling method and physical information embedding modeling method were introduced and analyzed in detail. It is found that the data-driven aerothermal modeling prediction method is not only more accurate than the engineering algorithm, but also can effectively reduce the workload of test measurement and numerical calculation when combined with the sampling method, and the model given is more efficient and concise. Finally, the develop- ment trend of data-driven aerothermal modeling prediction methods was prospected. It is pointed out that the deep combination of data-driven technology and classical aerothermal prediction methods, aerothermal physical information embedding modeling methods and aerothermal prediction big models will be the key points of future research.

Efficient Flow Field Reconstruction Based on Ensemble Transform Kalman Filter

GUO Yuxin, HUANG Jun, ZHAO Qingyu, JI Jingjing, HUANG Yongan

, Available online , doi: 10.19527/j.cnki.2096-1642.1090

34

6

Abstract:
Accurate estimation of turbulence field is of great importance in aerospace, and existing means of obtaining turbulence field is inadequate in terms of resolution or accuracy. Experimental measurements are accurate but often have a limited number of observation points, and numerical computations can obtain full-field data but the accuracy is difficult to guarantee. The data assimilation method integrates experimental observation and numerical simulation, which is an effective tool for flow field reconstruction. This paper explored the effectiveness of data assimilation method based on ensemble transform Kalman filter(ETKF) in spatial flow field reconstruction, and also discussed the reconstruction accuracy and computational efficiency of different iterative updates, namely ETKF-M and ETKF-D, which update state variables based on turbulence model and flow field data respectively. Using the ONERA M6 airfoil as a numerical example, the algorithm was experimented by combining the pressure measurement data from 271 pressure holes on the airfoil surface from the wind tunnel test. The results show that different iterative updates of ETKF method can effectively modify the prediction of the turbulence model, and the ETKF-D improves the computational efficiency by 83% compared with the ETKF-M. In addition, two groups of 1/4 experimental observation points at different locations were selected for assimilation experiments, and results with different accuracies were obtained. It indicates that the accuracy of reconstruction is closely related to the location and number of assimilated observation points.

Accuracy of MUSCL and WENO Schemes On Non-Uniform Structured Meshes

LIU Jun, LIU Yu

, Available online , doi: 10.19527/j.cnki.2096-1642.1079

17

4

Abstract:
The difference schemes constructed on the basis of one-dimensional uniform grids must be extended to non-uniform or curvilinear grids in practical applications, and the coordinate transformation process introduces geometry-induced errors. The accuracy of the difference schemes is evaluated by the accuracy test, in which the convergence solution error varies with the grid refinement. In this paper, the first-order upwind scheme, the second-order MUSCL scheme and the fifth-order WENO scheme were used to calculate the uniform free flow problem with constant flow parameters on a two-dimensional cylindrical coordinate uniform grid system, and the slope of the convergence curve was compared according to the ac- curacy test method, and it was found that the grid convergence accuracy of the first-order upwind scheme was second order, and the grid convergence accuracy of the fifth-order WENO scheme was less than first order. Theoretical analysis shows that this accuracy test method is not equivalent to the definition of difference scheme accuracy, and the data used cannot reflect the inherent defects of the difference scheme. Therefore, it cannot be used as a criterion for evaluating the accuracy of the difference scheme. Many studies of WENO schemes often simulate benchmarks such as the double Mach reflection problem and the two-dimensional Riemann problem, and use whether the contact discontinuity develops into an unstable vortex structure as a characteristic of the algorithm with high accuracy, which can be theoretically proved to be a non-physical phenomenon, so it is not appropriate to use whether a vortex structure appears as an argument for the algorithm's high accuracy.

Scale Interactions of Turbulent Boundary Layer Flows Under Local Dynamic Wall Disturbance

ZHANG Yu, TANG Zhan-qi, CUI Xiao-tong, JIANG Nan

, Available online , doi: 10.19527/j.cnki.2096-1642.1099

19

2

Abstract:
This paper analysed the relationships between various scales by considering the condition of the upstream flow fields. The feasibility of flow control for drag reduction through intermittent energy input from active drag reduction systems was discussed. In the experiment, a piezoelectric oscillator was used to impose local disturbances on a turbulent boundary layer. Flow field information was collected using fixed probes upstream of the piezoelectric oscillator and moving probes downstream (moving along the wall-normal direction). Correlation analyses were performed on velocity signals of different scales both upstream and downstream of the piezoelectric oscillator to determine their spatiotemporal relationships. Distur- bance signals and their higher-order harmonics were identified through the pre-multiplied energy spectrum, and different signal scales were categorized. The interactions between large scales and disturbance scales, as well as between disturbance scales and small scales, were particularly discussed under large-scale high-speed/low-speed inflow backgrounds. It is ob- served that the large-scale high-speed background modulates the disturbance signals. Under both large-scale high-speed and low-speed inflow backgrounds, there exists a fixed phase correspondence between the disturbance signals and small-scale signals, which remains unaffected by the inflow background. It is explicitly stated that when actively controlling the flow field intermittently using a piezoelectric oscillator, it is advisable to operate under a large-scale high-speed inflow back- ground.

Experiment for Heat Transport and Flow Structure of a Two-Layer Thermal Convection

WANG Mu, CHEN Yang, WANG Wei, WEI Ping

, Available online , doi: 10.19527/j.cnki.2096-1642.1066

45

6

Abstract:
Two-layer thermal convection exists widely in nature. In the present work, an experiment was conducted to inves- tigate the heat transport and flow structure in two-layer thermal convection. In a rectangular convection cell, two immiscible fluids, glycerol and 2 cs silicone oil, were used as the working fluids. In the lower-thin glycerol layer, the bottom boundary was subjected to a no-slip boundary condition (BC), and the interface was subjected to slip BC. The aspect ratio of glycerol layer (lower) was Γ₁=10.4. The Rayleigh number and Prandtl number of the glycerol layer covered the ranges of 260 ≤ Ra₁ ≤ 6 000 and 3 708<Pr₁<7 000, respectively. In the upper-thick silicone oil layer, the boundary at the top was subjected to no-slip BC. The aspect ratio of silicone oil (upper) was Γ₂=0.53. The Rayleigh number and Prandtl number of the silicone oil layer covered the ranges of 1.5×10⁹ ≤ Ra₂ ≤ 2.0×10¹⁰ and 28<Pr₂ <33. It is found that the two-layer thermal convection has different heat transfer efficiencies and flow structures in two regions. For region 1 where the heat flux is smaller than a certain value, the glycerol layer (lower) is in a stable stratified state. For region 2 where the heat flux is greater than the certain value, a cellular pattern was formed in glycerol layer and the global heat transport was sharply increased through a subcritical bifurcation. The heat transport of glycerol layer exhibits oscillatory instability at the critical Rayleigh number Ra_1c=1 523, which is smaller than the theoretic value 1 708 of critical value Ra for the 2D infinite Rayleigh-Bénard convection (RBC) with both rigid BCs. It reveals that the slip BC makes the fluid become unstable easier and enhances the heat transport. A measurement with shadowgraph method was further conducted. The cellular pattern of glycerol layer, the interface and hot plumes were also studied.

Experiment on Shock Wave Control of a Hypersonic Vehicle Standard Model Based on Plasma Synthetic Jet

XIE Wei, HU Guo-tun, SHI Wei, ZHOU Yan, LU Hong-bo, LUO Zhen-bing

, Available online , doi: 10.19527/j.cnki.2096-1642.1065

59

Abstract:
The novel active flow control technology based on plasma synthetic jet (PSJ) has great application potential in the field of shock wave control due to its advantages such as no gas source, strong control ability and wide excitation frequency band. The control effect of single-pulsed PSJ on head bow shock and wing shock of a hypersonic vehicle model and the drag reduction effect were experimentally studied in a hypersonic wind tunnel. The results show that the opposing PSJ can significantly increase the standoff distance of the head bow shock, and the transverse PSJ can basically eliminate the wing shock completely. The maximum instantaneous drag reduction rate of the vehicle measured by the dynamic force sensor is about 15.5%, but the drag change measured by the sensor has a delay of about 250 μs. The influence of discharge energy, incoming flow total pressure, exit diameter and cavity volume on the control effect of the head bow shock was also studied.

Supervised by：	China Aerospace Science and Technology Corporation
Sponsored by：	China Academy of Aerospace Aerodynamics Chinese Society of Astronautics China Aerospace Publishing House Co., LTD

Online First

Download Center

Contact Us

Links