Interaction of Shock Train with Cavity Shear Layer in a Scramjet Isolator

The interaction between the self-excited shock train flow and the cavity shear layer in a scramjet isolator is investigated numerically using detached-eddy simulations (DES). The effect of changing the position of the shock train by controlling the back pressure ratio and the effect of changing the cavity front wall angle are analyzed using unsteady statistics and modal analysis. The propagation mechanism of the pressure disturbance was investigated by spatiotemporal cross-correlation coefficient analysis. In the present numerical study, a constant isolator section with a cavity front wall was considered, followed by a diffuser section simulated at Mach number 2.2 with three different back pressure ratios. The change in back pressure provides three different conditions. To understand the unsteady dynamics of the interaction of the shear layer with the shock train, the spatiotemporal trajectory of the wall pressure and the centerline pressure distribution, the spatiotemporal cross-correlation coefficient, and the modal analysis by dynamic mode decomposition are obtained. The results show that the low-frequency shock train oscillation dominates the cavity oscillation. The spatiotemporal cross-correlation between the wall surface and the cavity bottom wall indicates the propagation of local disturbances originating from the separated boundary layer caused by the shock and the recirculation zone in the corners of the cavity. Dynamic mode decomposition analysis shows the shear layer at the leading edge of the cavity and the downstream propagation of large eddies from the cavity. It also shows the pairing of coherent structures between the shock train and the recirculation zone of the cavity.Comment: Submitted to Physics of Flui

Yay benzetimli çözüm ağı deformasyon tekniğinin kanat kesiti tasarımı en iyileştileştirilmesinde uygulanması.

In this thesis, an airfoil design optimization with Computational Fluid Dynamics (CFD) analysis combined with mesh deformation method is elaborated in detail. The mesh deformation technique is conducted based on spring analogy method. Several improvements and modifications are addressed during the implementation of this method. These enhancements are made so that good quality of the mesh can still be maintained and robustness of the solution can be achieved. The capability of mesh deformation is verified by considering rotating case of an airfoil for both inviscid and viscous meshes. The edge connectivity required in the spring analogy itself is computed by several simple algorithms. It is found that the presence of modified spring analogy technique leads to better solution in mesh deformation technique. Regarding the aerodynamic design optimization, SU2 3.2.9 open source software is used as the CFD Solver. During the computation, the initial mesh used in the optimization is obtained from Pointwise® mesh generation software. OPTLIB Gradient Optimizer of Phoenix Model Center is implemented as the optimization solver. The optimization process is conducted for four different flight conditions. In each flight condition, minimizing airfoil drag becomes the objective function with different angle of attack constraints imposed. Furthermore, several shape parameterizations are utilized. It is found that in each case, optimized airfoil can be found based on the designated design variables.M.S. - Master of Scienc

Comparison of Various Spring Analogy Mesh Deformation Techniques in 2 D Airfoil Design Optimization

During the last few decades, CFD (Computational Fluid Dynamics) has developed greatly and has become a more reliable tool for the conceptual phase of aircraft design. This tool is generally combined with an optimization algorithm. In the optimization phase, the need for regenerating the computational mesh might become cumbersome, especially when the number of design parameters is high. For this reason, several mesh generation and deformation techniques have been developed in the past decades. One of the most widely used techniques is the Spring Analogy. There are numerous spring analogy related techniques reported in the literature: linear spring analogy, torsional spring analogy, semitorsional spring analogy, and ball vertex spring analogy. This paper gives the explanation of linear spring analogy method and angle inclusion in the spring analogy method. In the latter case, two di¨erent solution methods are proposed. The best feasible method will later be used for two-dimensional (2D) Airfoil Design Optimization with objective function being to minimize sectional drag for a required lift coe©cient at di¨erent speeds. Design variables used in the optimization include camber and thickness distribution of the airfoil. SU2 CFD is chosen as the §ow solver during the optimization procedure. The optimization is done by using Phoenix ModelCenter Optimization Tool

Implementation of ball-center spring analogy mesh deformation technique with CFD design optimization

© 2015, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Mesh deformation technique plays an important role in several numerical simulations and applications including design optimization. This paper aims to implement the developed unstructured mesh deformation technique for CFD Design Optimization around 2-D Airfoils. During the optimization procedure, the newly deformed mesh is generated by using the updated Ball-Center Spring analogy mesh deformation technique. The comparison to the traditional Spring Analogy mesh deformation technique is made as well. SU2 Open Source flow solver is used for performing the CFD Analysis, where a viscous solver is utilized. The optimization processs is done by using Optimization Solver in Phoenix Model Center. In the optimization, the objective function is to minimize the drag, while keeping the generated lift to be constant

Assessment of re-entry survivability of aluminum oxide with different nanostructures considering surface catalytic heat-transfer

Re-entry survivability analysis is generally performed with the assumption of a smooth surface, for which the effect of surface roughness can be ignored. In such an approach, analysis may not provide accurate estimation of the survivability analysis of the re-entry object. The material surface roughness is known to enhance the surface catalytic properties of the material and thus results in a higher heat transfer. The present work incorporates the influence of surface roughness into the re-entry analysis in terms of surface catalytic recombination efficiency. The material catalytic efficiency value is obtained by using catalytic heat transfer theory in the shock tube end-wall heat transfer measurement. The material considered in the analysis is aluminum oxide with various levels of surface roughness. The roughness is varied by mechanical abrasion by using silicon carbide (SiC) sandpaper. The quality of the material is also assessed with different characterization techniques that include EDS, XPS, and AFM measurement. Through experimental measurement, it is observed that the surface catalytic recombination efficiency increases as the surface roughness level increases. Using the obtained efficiency values, the re-entry survivability analysis shows that a material with a high level of surface roughness exhibits a low survivability rate

Improvement in the spring analogy mesh deformation method through the cell-center concept

The mesh deformation method is an important topic in studies involving moving boundary problems. As one of the main approaches, this method has been applied in various related studies. To address the cell inversion problem encountered in the spring analogy mesh deformation method, the present study proposes an improvement in it by cell-center concept. In addition to the linear spring between two nodal points on the mesh, the cell-center concept introduces additional fictitious springs between the cell-center and its nodal points. The spring constants for both actual and fictitious springs are modeled as reciprocals of the spring length. The final coordinates for each nodal point on the mesh are updated by assuming an equilibrium condition is achieved. For benchmark testing, the proposed method is compared with the original spring analogy and torsional spring analogy methods for rotating airfoil with inviscid mesh and multi-element airfoil with viscous mesh. It is observed that the cell-center spring analogy method alleviates the cell inversion problem that occurs in the original spring analogy method. Discussion concerning the performance of each method for the comparison is also included

Effect of equilibrium constant for carbon dioxide recombination in hypersonic flow analysis

An equilibrium constant is an important parameter in regard to determining the backward reaction rate constant in chemical kinetics modeling for a hypersonic flow. Three common approaches for the equilibrium constant determination are based on the partition function, Gibbs free energy, and the experimental reaction rate measurement. The present study conducted a computational fluid dynamics (CFD) analysis with different equilibrium constant formulations in a thermochemical nonequilibrium hypersonic flow in order to study the influence of the equilibrium constant in carbon dioxide flow during the Martian entry. The equilibrium constant for the carbon dioxide molecule dissociation differs from one method to another among the reactions that are considered in the carbon dioxide flow. Three different flow conditions, which are based on the experimental data that is provided in the literature, are considered in the detailed comparison analysis using CFD. The variation of the flow properties in terms of pressure, temperature, and mass fraction along the stagnation line is compared for different cases of the equilibrium constant computation. The results that are obtained from the present study confirm that the equilibrium constant influences the numerical computation in the thermochemical nonequilibrium flow especially for the non-catalytic wall boundary condition

Konvansiyonel ve Konvansiyonel Olmayan Kontrol Yüzeylerine Sahip İnsansız Hava Aracı Kanatlarının Aerodinamik Özelliklerinin Değerlendirilmesi

Bu bildiride insansız hava aracına ait bir kanattaki kontrol yüzeyleri konvansiyonel ve konvansiyonel olmayan iki farklı konfigürasyonda aerodinamik açıdan incelenmiştir. Aerodinamik analizler için Pointwise® V17.0- R2 ve SU2 V2.0.001 adlı paket programlar kullanılmıştır. Konvansiyonel kontrol yüzeylerini hareket ettirebilecek tork miktarı aerodinamik veriler kullanılarak hesaplanmıştır. Konvansiyonel olmayan kontrol yüzeylerini hareket ettirecek tork miktarı ise bu çalışmadaki aerodinamik verileri kullanarak diğer bir çalışmada hesaplanmıştırIn this work, aerodynamic analysis of an unmanned aerial vehicle wing having conventional and unconventional control surfaces was conducted. Pointwise® V17.0-R2 and SU2 V2.0.001 package programs were used for the analysis. Required torque to deflect conventional control surfaces was calculated by using aerodynamic data obtained from the analysis. Required torque to deflect unconventional control surfaces was calculated in another proceeding using aerodynamic data obtained in this stud