Numerical Simulation Of High Lift Devices In Unsteady Ground Effect

High lift devices are most frequently utilized during the take-off and landing phases of civil aircrafts.The distance between an aircraft and the ground varies when it approaches the ground,therefore the aircraft will be influenced by the unsteady ground effect.Based on unsteady N-S equations and dynamic grid method,unsteady ground effects of high lift devices has been simulated to clarify the aerodynamics theory and performance,which can direct the design and performance evaluation of high lift devices,hence it is of significant value of engineering application.In cases of large mesh deformation of aircrafts' landing,the cumulative error caused by the discrete procedure in the GCL could significantly increases,and a direct consequence is that the calculated cell volume may become non-physical.In response to this question,a new Discrete GCL(D-GCL)is proposed in this paper.Error analysis indicates that the truncation error of the numerical scheme is guaranteed to be the same order as that obtained from the original D-GCL,while the accumulated error is greatly reduced.Given that the deformation of internal nodes is subject to edges in a multi-block structured grid,a hybrid dynamic grid technique based on TFI and Modified Shepard Algorithm is presented: At first,apply Modified Shepard Algorithm to get the grid deformation on block edges.Then an arc-length-based TFI is employed to efficiently calculate the grid deformation on block faces and internal nodes of each block.Finally,local reconstruction is adopted to guarantee mesh quality if necessary.On the basis of above dynamic grid method,numerical simulation of two-dimensional unsteady ground effect is presented,computation of single/two-element airfoil's landing is performed and unsteady ground effect is analyzed.Besides,the results are compared with the steady(irrespective of airfoil's descent)and quasi-steady(add the equivalent attack angle to airfoil's attack angle)ones.Furthermore,numerical simulation is expanded to three-dimensional cases and the landing process of single wing and wing-body with high lift devices is researched respectively.Similarly,the results are compared with the steady and quasi-steady ones.Reduce the deployment and retraction of high lift devices to the model of slat and flap rotates around corresponding axis,so that numerical simulation of deployment and retraction of high lift devices based on unsteady N-S equations and the dynamic method is realized.Unsteady flow around the airfoil and aircraft of a certain ride height is investigated respectively,and the results are compared with the steady ones.