scholarly journals Aerodynamics Analysis of Grid Fins Inner Lattice Structure in Cruise Missile

2021 ◽  
Vol 16 ◽  
pp. 92-101
Author(s):  
Sharul Sham Dol
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Lattice Structure ◽  
Cruise Missile ◽  
Width Ratio ◽  
Lattice Structures ◽  
Scaled Model ◽  
Fine Control ◽  
Cruise Missiles ◽  
Stability And Accuracy

Grid fins are normally placed at the rear end of cruise missiles, rockets and other ballistic devices to control their trajectory especially at the final stage of flight. These fins provided fine control of the pitch, yaw and other lateral movements, allowing for higher stability and accuracy of the cruise missiles. This project investigates computationally the relation between grid fins inner lattice structures dimensionless parameters and the fins aerodynamics drag coefficient. The project gathered data from 12 different fins by varying the parameters of its internal lattice structure such as thickness, width and chord at various angles of attack (0°, 20° and 40°). The freestream was set at a constant speed of 150 m/s that gives Reynolds number > 1.7 x 106 . The results were experimentally compared by using a re-scaled model of a single fin in a sub-sonic wind tunnel, achieving a difference in results of not exceeding 6%. The results obtained that as the width-chord ratio increases, the aerodynamics drag coefficient increases for fixed thickness-width ratio. The results also demonstrated that as the angle of attack increases, the aerodynamics drag increases. The thickness-width ratio has the larger impact on the aerodynamics drag. The results can be used to improve the design of guided cruise missiles.

scholarly journals Determination of the drag coefficient of lattice structures under wind load using porous media approach

2021 ◽  
pp. 233-233
Author(s):  
Milada Pezo ◽  
Nikola Mirkov ◽  
Vukman Bakic
Keyword(s):  
Drag Coefficient ◽  
Lattice Structure ◽  
Three Dimensional ◽  
Reynolds Stress Model ◽  
International Standards ◽  
Lattice Structures ◽  
Three Dimensional Model ◽  
Aerodynamic Forces ◽  
Wind Velocities ◽  
The Stability

The power transmitters, guyed masts and other lattice structures are exposed to wind action. The aerodynamic forces acting on tall tower constructions have crucial importance on the stability of the structure. The lattice structure drag coefficient determination is the subject of the international standards ESDU 81027 and 81028 and Eurocode 3 Part 3.1, but it can also be determined by numerical methods. For that purpose modeling using Computational Fluid Dynamics (CFD) proved to be both accurate and reliable. In this study the fluid flow around the segment of a power transmitter was simulated by a three-dimensional model, where the geometry of the segment is approximated with a porous structure having the appropriate factor of porosity, in order to simplify the geometry. We have used three representative models of turbulence, standard k-? model, RNG k-? model and Reynolds Stress Model. Drag coefficient values are extracted from the flow field and compared for all studied cases and with available experimental results from the wind tunnel. Simulations were performed for four wind velocities between 10 m/s and 30 m/s. The results are supplemented by the ones obtained by Artificial Neural Network. The aim of this study is to show how the simple turbulence model coupled with approximated geometry can be used in the analysis of the aerodynamic forces acting on the lattice structure.

scholarly journals Simulation of Gas Flow Over a Micro Cylinder

2009 ◽  
Author(s):  
Yuan Hu ◽  
Quanhua Sun ◽  
Jing Fan
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Drag Coefficient ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Low Reynolds Number ◽  
Pressure Drag ◽  
Low Reynolds ◽  
Rarefied Gas Effect ◽  
Gas Effect

Gas flow over a micro cylinder is simulated using both a compressible Navier-Stokes solver and a hybrid continuum/particle approach. The micro cylinder flow has low Reynolds number because of the small length scale and the low speed, which also indicates that the rarefied gas effect exists in the flow. A cylinder having a diameter of 20 microns is simulated under several flow conditions where the Reynolds number ranges from 2 to 50 and the Mach number varies from 0.1 to 0.8. It is found that the low Reynolds number flow can be compressible even when the Mach number is less than 0.3, and the drag coefficient of the cylinder increases when the Reynolds number decreases. The compressible effect will increase the pressure drag coefficient although the friction coefficient remains nearly unchanged. The rarefied gas effect will reduce both the friction and pressure drag coefficients, and the vortex in the flow may be shrunk or even disappear.

Determination of Optimal Unit-Cell Size of Homogeneous Conformal Unit-Cell Lattice Structure Using Solid Shape Matching

2016 ◽  
Author(s):  
Mahmoud A. Alzahrani ◽  
Seung-Kyum Choi
Keyword(s):  
Cell Size ◽  
Solid Body ◽  
Strain Energy ◽  
Lattice Structure ◽  
Weight Ratio ◽  
Unit Cell ◽  
Optimal Size ◽  
Lattice Structures ◽  
Unit Cell Size ◽  
Unit Cells

With rapid developments and advances in additive manufacturing technology, lattice structures have gained considerable attention. Lattice structures are capable of providing parts with a high strength to weight ratio. Most work done to reduce computational complexity is concerned with determining the optimal size of each strut within the lattice unit-cells but not with the size of the unit-cell itself. The objective of this paper is to develop a method to determine the optimal unit-cell size for homogenous periodic and conformal lattice structures based on the strain energy of a given structure. The method utilizes solid body finite element analysis (FEA) of a solid counter-part with a similar shape as the desired lattice structure. The displacement vector of the lattice structure is then matched to the solid body FEA displacement results to predict the structure’s strain energy. This process significantly reduces the computational costs of determining the optimal size of the unit cell since it eliminates FEA on the actual lattice structure. Furthermore, the method can provide the measurement of relative performances from different types of unit-cells. The developed examples clearly demonstrate how we can determine the optimal size of the unit-cell based on the strain energy. Moreover, the computational cost efficacy is also clearly demonstrated through comparison with the FEA and the proposed method.

Guidelines for CFD Simulations of Spar VIM

2013 ◽  
Author(s):  
Charles Lefevre ◽  
Yiannis Constantinides ◽  
Jang Whan Kim ◽  
Mike Henneke ◽  
Robert Gordon ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Test Data ◽  
Model Test ◽  
Model Tests ◽  
Full Scale ◽  
Mooring System ◽  
Time Step ◽  
Cfd Simulations ◽  
Scaled Model ◽  
Sway Motion

Vortex-Induced Motion (VIM), which occurs as a consequence of exposure to strong current such as Loop Current eddies in the Gulf of Mexico, is one of the critical factors in the design of the mooring and riser systems for deepwater offshore structures such as Spars and multi-column Deep Draft Floaters (DDFs). The VIM response can have a significant impact on the fatigue life of mooring and riser components. In particular, Steel Catenary Risers (SCRs) suspended from the floater can be sensitive to VIM-induced fatigue at their mudline touchdown points. Industry currently relies on scaled model testing to determine VIM for design. However, scaled model tests are limited in their ability to represent VIM for the full scale structure since they are generally not able to represent the full scale Reynolds number and also cannot fully represent waves effects, nonlinear mooring system behavior or sheared and unsteady currents. The use of Computational Fluid Dynamics (CFD) to simulate VIM can more realistically represent the full scale Reynolds number, waves effects, mooring system, and ocean currents than scaled physical model tests. This paper describes a set of VIM CFD simulations for a Spar hard tank with appurtenances and their comparison against a high quality scaled model test. The test data showed considerable sensitivity to heading angle relative to the incident flow as well as to reduced velocity. The simulated VIM-induced sway motion was compared against the model test data for different reduced velocities (Vm) and Spar headings. Agreement between CFD and model test VIM-induced sway motion was within 9% over the full range of Vm and headings. Use of the Improved Delayed Detached Eddy Simulation (IDDES, Shur et al 2008) turbulence model gives the best agreement with the model test measurements. Guidelines are provided for meshing and time step/solver setting selection.

Settling Behavior of Particles in Bubble Containing Newtonian Fluids: Experimental Study and Model Development

2021 ◽  
Author(s):  
Silin Jing ◽  
Xianzhi Song ◽  
Zhaopeng Zhu ◽  
Buwen Yu ◽  
Shiming Duan
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Volume Concentration ◽  
Settling Velocity ◽  
Particle Density ◽  
Particle Diameter ◽  
Newtonian Fluids ◽  
Spherical Particles ◽  
Bubble Volume ◽  
Particle Reynolds Number

Abstract Accurate description of cuttings slippage in the gas-liquid phase is of great significance for wellbore cleaning and the control accuracy of bottom hole pressure during MPD. In this study, the wellbore bubble flow environment was simulated by a constant pressure air pump and the transparent wellbore, and the settling characteristics of spherical particles under different gas volume concentrations were recorded and analyzed by highspeed photography. A total of 225 tests were conducted to analyze the influence of particle diameter (1–12mm), particle density (2700–7860kg/m^3), liquid viscosity and bubble volume concentration on particle settling velocity. Gas drag force is defined to quantitatively evaluate the bubble’s resistance to particle slippage. The relationship between bubble drag coefficient and particle Reynolds number is obtained by fitting the experimental results. An explicit settling velocity equation is established by introducing Archimedes number. This explicit equation with an average relative error of only 8.09% can directly predict the terminal settling velocity of the sphere in bubble containing Newtonian fluids. The models for predicting bubble drag coefficient and the terminal settling velocity are valid with particle Reynolds number ranging from 0.05 to 167 and bubble volume concentration ranging from 3.0% to 20.0%. Besides, a trial-and-error procedure and an illustrative example are presented to show how to calculate bubble drag coefficient and settling velocity in bubble containing fluids. The results of this study will provide the theoretical basis for wellbore cleaning and accurate downhole pressure to further improve the performance of MPD in treating gas influx.

A Proof of Concept Study of the Mechanical Behavior of Lattice Structures Used to Design a Shoulder Hemi-Prosthesis

2021 ◽  
Author(s):  
Marinela Peto ◽  
Oscar Aguilar-Rosas ◽  
Erick Erick Ramirez-Cedillo ◽  
Moises Jimenez ◽  
Adriana Hernandez ◽  
...  
Keyword(s):  
Mechanical Behavior ◽  
Mechanical Response ◽  
Mechanical Performance ◽  
Cell Attachment ◽  
Lattice Structure ◽  
Material Model ◽  
Patient Specific ◽  
Hexagonal Prism ◽  
Lattice Structures ◽  
Proof Of Concept

Abstract Lattice structures offer great benefits when employed in medical implants for cell attachment and growth (osseointegration), minimization of stress shielding phenomena, and weight reduction. This study is focused on a proof of concept for developing a generic shoulder hemi-prosthesis, from a patient-specific case of a 46 years old male with a tumor on the upper part of his humerus. A personalized biomodel was designed and a lattice structure was integrated in its middle portion, to lighten weight without affecting humerus’ mechanical response. To select the most appropriate lattice structure, three different configurations were initially tested: Tetrahedral Vertex Centroid (TVC), Hexagonal Prism Vertex Centroid (HPVC), and Cubic Diamond (CD). They were fabricated in resin by digital light processing and its mechanical behavior was studied via compression testing and finite element modeling (FEM). The selected structure according to the results was the HPVC, which was integrated in a digital twin of the biomodel to validate its mechanical performance through FEM but substituting the bone material model with a biocompatible titanium alloy (Ti6Al4V) suitable for prostheses fabrication. Results of the simulation showed acceptable levels of Von Mises stresses (325 MPa max.), below the elastic limit of the titanium alloys, and a better response (52 MPa max.) in a model with equivalent elastic properties, with stress performance in the same order of magnitude than the showed in bone’s material model.

scholarly journals Dynamic Loading of Lattice Structure Made by Selective Laser Melting-Numerical Model with Substitution of Geometrical Imperfections

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2129 ◽  
Author(s):  
Radek Vrána ◽  
Ondřej Červinek ◽  
Pavel Maňas ◽  
Daniel Koutný ◽  
David Paloušek
Keyword(s):  
Mechanical Properties ◽  
Numerical Model ◽  
Cross Section ◽  
Lattice Structure ◽  
Low Velocity Impact ◽  
Lattice Structures ◽  
Laser Melting ◽  
Low Velocity ◽  
Velocity Impact ◽  
Geometrical Imperfections

Selective laser melting (SLM) is an additive technology that allows for the production of precisely designed complex structures for energy absorbing applications from a wide range of metallic materials. Geometrical imperfections of the SLM fabricated lattice structures, which form one of the many thin struts, can lead to a great difference in prediction of their behavior. This article deals with the prediction of lattice structure mechanical properties under dynamic loading using finite element method (FEA) with inclusion of geometrical imperfections of the SLM process. Such properties are necessary to know especially for the application of SLM fabricated lattice structures in automotive or aerospace industries. Four types of specimens from AlSi10Mg alloy powder material were manufactured using SLM for quasi-static mechanical testing and determination of lattice structure mechanical properties for the FEA material model, for optical measurement of geometrical accuracy, and for low-velocity impact testing using the impact tester with a flat indenter. Geometries of struts with elliptical and circular cross-sections were identified and tested using FEA. The results showed that, in the case of elliptical cross-section, a significantly better match was found (2% error in the Fmax) with the low-velocity impact experiments during the whole deformation process compared to the circular cross-section. The FEA numerical model will be used for future testing of geometry changes and its effect on mechanical properties.

Topology, Shape, and Size Optimization of Additively Manufactured Lattice Structures Based on the Superformula

2018 ◽  
Author(s):  
Andrea Nessi ◽  
Tino Stanković
Keyword(s):  
Lattice Structure ◽  
Lightweight Design ◽  
Mathematical Formulation ◽  
Lattice Structures ◽  
Structural Synthesis ◽  
Normal Surface ◽  
Technical Problems ◽  
Wide Range ◽  
Tetrahedral Meshing

This paper investigates the application of Superformula for structural synthesis. The focus is set on the lightweight design of parts that can be realized using discrete lattice structures. While the design domain will be obtained using the Superformula, a tetrahedral meshing technique will be applied to this domain to generate the topology of the lattice structure. The motivation for this investigation stems from the property of the Superformula to easily represent complex biological shapes, which opens a possibility to directly link a structural synthesis to a biomimetic design. Currently, numerous results are being reported showing the development of a wide range of design methods and tools that first study and then utilize the solutions and principles from the nature to solve technical problems. However, none of these methods and tools quantitatively utilizes these principles in the form of nature inspired shapes that can be controlled parametrically. The motivation for this work is also in part due to the mathematical formulation of the Superformula as a generalization of a superellipse, which, in contrast to the normal surface modeling offers a very compact and easy way to handle set of rich shape variants with promising applications in structural synthesis. The structural synthesis approach is organized as a volume minimization using Simulated Annealing (SA) to search over the topology and shape of the lattice structure. The fitness of each of candidate solutions generated by SA is determined based on the outcome of lattice member sizing for which an Interior Point based method is applied. The approach is validated with a case study involving inline skate wheel spokes.

Drag optimisation of a wing equipped with a morphing upper surface

2016 ◽  
Vol 120 (1225) ◽  
pp. 473-493 ◽  
Author(s):  
A. Koreanschi ◽  
O. Sugar-Gabor ◽  
R. M. Botez
Keyword(s):  
Genetic Algorithm ◽  
Reynolds Number ◽  
Drag Coefficient ◽  
Open Source ◽  
Experimental Testing ◽  
Shape Reconstruction ◽  
Laminar To Turbulent Transition ◽  
Wing Model ◽  
Turbulent Transition ◽  
Transition Delay

ABSTRACTThe drag coefficient and the laminar-to-turbulent transition for the aerofoil component of a wing model are optimised using an adaptive upper surface with two actuation points. The effects of the new shaped aerofoils on the global drag coefficient of the wing model are also studied. The aerofoil was optimised with an ‘in-house’ genetic algorithm program coupled with a cubic spline aerofoil shape reconstruction and XFoil 6.96 open-source aerodynamic solver. The wing model analysis was performed with the open-source solver XFLR5 and the 3D Panel Method was used for the aerodynamic calculation. The results of the aerofoil optimisation indicate improvements of both the drag coefficient and transition delay of 2% to 4%. These improvements in the aerofoil characteristics affect the global drag of the wing model, reducing it by up to 2%. The analyses were conducted for a single Reynolds number and speed over a range of angles of attack. The same cases will also be used in the experimental testing of the manufactured morphing wing model.

Mixing Characteristics of a Two-Phase Flow (Gas-Liquid) Microchannel Mixer

2011 ◽  
Author(s):  
Tarek Abdel-Salam ◽  
Srikanth Pidugu
Keyword(s):  
Reynolds Number ◽  
Two Phase Flow ◽  
Bubble Formation ◽  
Width Ratio ◽  
Phase Flow ◽  
Two Phase ◽  
Bubble Generation ◽  
Air Bubble ◽  
And Performance ◽  
Actual Shape

Multiphase phase flows occur in many engineering and bio-medical applications. Bubble formation in microchannels can be beneficial or harmful depending upon their influence on the operation and performance of microfludic devices. Potential uses of bubble generation found in many applications such as microreactors, micropump, and micromixers. In the present work the flow and mixing process in a passive microchannel mixer were numerically investigated. Effects of velocity, and inlet width ratio (Dgas/Dliquid) on the two phase flow were studied. Numerical results are obtained for 2-dimensional and 3-dimesional cases with a finite volume CFD code and using structured grids. Different liquid-gas Reynolds number ratios (Reliquid/Regas) were used ranging from 4 to 42. In addition, three values of the inlet width ratio (Dgas/Dliquid) were used. Results for the 3-D cases capture the actual shape of the air bubble with the thin film between the bubble and the walls. Also, increasing Reliquid increases the rate of the development of the air bubble. The bubble length increases with the increase of Dgas/Dliquid. For the same values of Re, the rate of growth of the bubble increases with the increase of Dgas/Dliquid. Finally, a correlation is provided to predict the length of the bubble with liquid-gas Reynolds number ratio (Reliquid/Regas) and tube width.

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