Sharif Digital Repository

This paper represents the detailed results of an evolutionary optimization framework towards the exploration of vortex mechanisms leading to effective anti-vortex film cooling. In this regards, several arrangements of triple cooling holes were studied on flat and curved geometries using differential-evolution optimization algorithm and a modified Reynolds-stress based flow solver. Depending on the flow and geometric parameters, four distinct types of vortex interaction with different cooling mechanisms were identified. The vortex-trapping mechanism, observed in the optimized upstream arrangement acts through imposing a mild downwash over the main counter-rotating vortex pair and provides the... 

An improved phenomenological model is presented for numerical simulation of a Dielectric Barrier Discharge (DBD) plasma actuator for separation control of high angle of attack flow over a wind turbine airfoil. Based on existing numerical models and experimental measurements, a new model is proposed for prediction of the length of a plasma extent which is more consistent with previous observations. The electrical and hydrodynamic solvers used in the present study are validated against published experimental data. Then the applicability of a DBD actuator, mounted on a DU 91-W2-250 airfoil is extensively analyzed for a wide range of operating voltages and frequencies. The analysis is completely... 

A shock control bump (SCB) is a flow control method which uses a local small deformation in a flexible wing surface to considerably reduce the strength of shock waves and the resulting wave drag in transonic flows. Most of the reported research is devoted to optimization in a single flow condition. Here, both equally and variably weighted multi-point optimization and a robust adjoint optimization scheme are used to optimize the SCB. The numerical simulation of the turbulent viscous flow and a gradient-based adjoint algorithm are used to find the optimum location and shape of the SCB for two benchmark aerofoils. A multi-point optimization method under a constant-lift-coefficient constraint is... 

Most researches on the application of the adjoint method in turbine blade design are concentrated on the aerodynamic shape optimization without considering the heat transfer to/from the blade material. In this study, the adjoint method is extended to the conjugate heat transfer problems in which the viscous flow field is coupled to heat transfer in the solid region. Introducing a new adjoint variable in the solid domain, a heat adjoint equation is derived which is coupled with the energy adjoint equation in the fluid zone at the fluid/solid interface. The detailed mathematical description associated with the derivation of the heat adjoint equation with corresponding boundary conditions are... 

A shock control bump (SCB) is a flow control method which uses local small deformations in a flexible wing surface to considerably reduce the strength of shock waves and the resulting wave drag in transonic flows. Most of the reported research is devoted to optimization in a single flow condition. Here, we have used a multi-point adjoint optimization scheme to optimize shape and location of the SCB. Practically, this introduces transonic airfoils equipped with the SCB which are simultaneously optimized for different off-design transonic flight conditions. Here, we use this optimization algorithm to enhance and optimize the performance of SCBs in two benchmark airfoils, i.e., RAE-2822 and... 

A shock control bump (SCB) is a flow control method that uses local small deformations in a flexible wing surface to considerably reduce the strength of shock waves and the resulting wave drag in transonic flows. Most of the reported research is devoted to optimization in a single flow condition. Here, we have used a multi-point adjoint optimization scheme to optimize shape and location of the SCB. Practically, this introduces transonic airfoils equipped with the SCB that are simultaneously optimized for different off-design transonic flight conditions. Here, we use this optimization algorithm to enhance and optimize the performance of SCBs in two benchmark airfoils, i.e., RAE-2822 and... 

Single-walled carbon nanotubes (SWCNTs) can be promising delivery nanodevices for a diverse range of applications, however, little is known about their dynamical interactions with moving nanoscale particles. In this paper, dynamic response of a SWCNT subjected to a moving nanoparticle is examined in the framework of the nonlocal continuum theory of Eringen. The inertial effects of the moving nanoparticle and the existing friction between the nanoparticle surface and the inner surface of the SWCNT are incorporated in the formulation of the problem. The equivalent continuum structure associated with the SWCNT is considered and modeled using nonlocal Rayleigh beam theory under simply supported... 

The free longitudinal vibration of tapered nanowires is investigated in the context of nonlocal continuum theory. The problem is studied for the nanowires with linearly varied radii under fixedfixed and fixedfree boundary conditions. In order to assess the problem in a more general form, a perturbation technique is proposed based on the Fredholm alternative theorem. The natural frequencies, corresponding mode shapes, and phase velocities of the tapered nanowires are derived analytically up to the second-order perturbation for different boundary conditions. The predicted results by the perturbation technique are successfully verified with those of the exact solution. The obtained results... 

A single-walled nanotube structure embedded in an elastic matrix is simulated by the nonlocal EulerBernoulli, Timoshenko, and higher order beams. The beams are assumed to be elastically supported and attached to continuous lateral and rotational springs to take into account the effects of the surrounding matrix. The discrete equations of motion associated with free transverse vibration of each model are established in the context of the nonlocal continuum mechanics of Eringen using Hamilton's principle and an efficient meshless method. The effects of slenderness ratio of the nanotube, small scale effect parameter, initial axial force and the stiffness of the surrounding matrix on the natural...