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CONTENTS
Volume 11, Number 2, June 2024
 

Abstract
Vibrations in aerodynamic systems can lead to significant structural and performance issues. This paper presents a novel theorem for actively controlling aerodynamic vibrations through parametric stability analysis. The proposed approach models the aerodynamic system as a dynamic system with parametric excitation, allowing for the identification of stable and unstable regions in the parameter space. By strategically adjusting the system parameters, the vibrations can be effectively suppressed, enhancing the overall reliability and performance of the aerodynamic system. The theoretical underpinnings of the theorem are discussed, and the effectiveness of the approach is demonstrated through numerical simulations and experimental validation. The results show the potential of this method for practical implementation in various aerodynamic applications, such as aerospace engineering and wind turbine design.

Key Words
aerodynamics; dynamic systems; parametric stability; structural dynamics; vibration control

Address
C.C. Hung: Faculty of National Hsin Hua Senior High School, Tainan, Taiwan
T. Nguyễn: Ha Tinh University, Dai Nai Ward, Ha Tinh City, Vietnam
C.Y. Hsieh: National Pingtung University Education School, No.4-18, Minsheng Rd., Pingtung City, Pingtung County, 900391, Taiwan

Abstract
The applicability of a novel incremental-iterative technique with 2D differential/integral quadrature method (DIQM) in analyzing the nonlinear behavior of Bi-directional functionally graded (BDFG) porous plate based on neutral surface is verified in the present works. A formulation of four variables high shear deformation theory is used to describe the kinematic relations with respect to neutral surface rather than mid-plane. Bi-directional material distributions are presented by power functions through both thickness and axial directions. Porosities and voids are distributed by different cosine functions. The large deformations are included within the sense of nonlinear von Kármán strains. The integro-differential equilibrium equations with associated modified boundary conditions are solved numerically and iteratively by using 2D DIQM. Model validations and parametric analysis are depicted to present the influence of neutral axis, nonlinear strains, gradation indices, elastic foundations, and modified boundary conditions on the static deflection in addition to normal and shear stresses. The proposed model is effective in analyzing the static behavior of many real applications in nuclear reactors, marine and aerospace structures with large deformations.

Key Words
2D differential integral quadrature method; incremental iterative technique; neutral surface; nonlinear coupled partial differential equations; nonlinear static analysis; Porous BDFG plate

Address
Amr E. Assie: Department of Mechanical Engineering, Faculty of Engineering, Jazan University, Jazan, Saudi Arabia; Department of Mechanical Design and Production, Faculty of Engineering, Zagazig University, Zagazig, Egypt

Abstract
In jet engines, turbine blade cooling has an extremely important role. The pin-fin array, which is situated close to the trailing edge of the blade, aids in internal cooling of the gas turbine blades and preserves the structural integrity of the blade. Previous studies often focused on pin-fin configurations, but the current research focuses on improving the geometry at the endwalls to reduce wake vortices behind the pin-fins and enhance heat transfer at the endwalls location. Using the k-w turbulence model, a numerical study was conducted on a ribbed shape situated on the walls between pin-fin arrays, spanning a Reynolds number range of 7400 to 36000, in order to determine the heat transport characteristics. The heat transfer efficiency coefficient and Nusselt number increase dramatically with the revised wall configuration, according to the numerical data. The channel's heat transfer efficiency is increased by enlarging the heat transfer areas near the pin-fins and by the interaction of the flow with the endwalls. The addition of ribs causes the Nusselt number of the new model to climb from 78% to 96% at the previously given Reynolds numbers, and the heat transfer efficiency index to rise from 60% to 73%. The height (Hr), position (Lr), forward width (Wf), and backward width (Wb) of the ribs are among the geometric elements that were looked at in order to determine how they affected the performance of heat transmission. In comparison to the reference design, the parametric study results demonstrate that the best forward width (Wf/R=18.75%) and backward width (Wb/R=31.25%) increase the heat transfer efficiency index by 0.4% and 1.3%, respectively.

Key Words
gas turbine blade; heat transfer efficiency index; nusselt number; pin-fin internal cooling; RANS analysis; ribbed endwalls

Address
Vu T.A. Co: Vietnam Aviation Academy, No. 104, Nguyen Van Troi Street, Ward 8, Phu Nhuan District, Ho Chi Minh City, Vietnam
Hung C. Hoang, Duy C.K. Do, Son H. Truong, Diem G. Pham, Nhung T.T. Le, Truong C. Dinh, Linh T. Nha: School of Mechanical Engineering, Hanoi University of Science and Technology, No. 1, Dai Co Viet Road, Hai Ba Trung District, Hanoi 11615, Vietnam

Abstract
The objective of this paper is to compute entire flow field over Apollo-II, Aerospace Reentry Demonstrator (ARD), Orbital Experiment (OREX) with sharp shoulder and rounded shape shoulder and Space Recovery Experiment (SRE) at different flare-cone half-angle of 20o and 35o. This paper addresses numerical solutions of the compressible three-dimensional Euler equations on hexahedral meshes for a freestream Mach 6 and at an angle of incidence 5o. Furthermore, spatial discretization is accomplished by a cell centred finite volume formulation solution and advanced in time by an explicit multi-stage Runge-Kutta method. The flow field characteristics, distribution of surface pressure coefficient and Mach number on fore-body and aft-body are presented as a function of the geometrical parameters of many reentry capsules. The surface pressure variation is numerically integrated to obtain the aerodynamic drag and compared well with impact theory. The present numerical study has observed the significant dependence of the blunt body and the aft-body geometry of the vehicle and can be used to study atmospheric conditions during re-entry trajectory. The numerical analysis reveals the significant influence of capsule geometry on the flow characteristics of the mechanism of upstream and structure of the flow near the wake region and aerodynamic drag coefficient.

Key Words
aerodynamics; base flow; computational fluid dynamics; hypersonic flow; reentry capsule; shock wave; surface pressure coefficient

Address
R.C. Mehta: Department of Aeronautical Engineering, Noorul Islam Centre for Higher Education, Kumaracoil 629180, India

Abstract
This article deals with the changes in flow air properties across an oblique shock wave for a real gas. The flow through is investigated to find a general form for oblique shock waves. The main objective of this work will result in the development of a new numerical algorithm to determine the effect of the stagnation pressure on supersonic flow for thermally and calorically imperfect gases with a molecular dissociation threshold, thus giving a better affinity to the physical behavior of the waves. So, the effects of molecular size and intermolecular attraction forces are used to correct a state equation, emphasizing the determination of the impact of upstream stagnation parameters on oblique shock waves. As results, the specific heat pressure does not remain constant and varies with the temperature and density. At Mach numbers greater than 2.0, the temperature rise considerably, and the density rise is well above, that predicted assuming ideal gas behavior. It is shown that caloric imperfections in air have an appreciable effect on the parameters developed in the processes is considered. Computation of errors between the present model based on real gas theory and a perfect gas model shows that the influence of the thermal and caloric imperfections associated with a real gas is important and can rise up to 16%.

Key Words
normal shock wave; oblique shock wave; perfect gas; real gas; supersonic air flow

Address
Mechta Mohammed, Yahiaoui Toufik: Aeronautical Sciences Laboratory, Institute of Aeronautics, and Space Studies University of Blida 1, BP 270 Blida 09000, Algeria
Dahia Ahmed: Nuclear Research Center of Birine, B.P 180, Ain Oussera 17200, Djelfa, Algeria

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