Mahdi Nili-Ahmadabadi

Bio: Mahdi Nili-Ahmadabadi is an academic researcher from Isfahan University of Technology. The author has contributed to research in topics: Reynolds number & Airfoil. The author has an hindex of 12, co-authored 70 publications receiving 411 citations. Previous affiliations of Mahdi Nili-Ahmadabadi include Sharif University of Technology.

A Novel 2D Incompressible Viscous Inverse Design Method for Internal Flows Using Flexible String Algorithm

Abstract: In this investigation, the flexible string algorithm (FSA), used before for inverse design of subsonic and supersonic ducts in compressible flows with and without normal shock, is developed and applied for inverse design of 2D incompressible viscous internal flow with and without separation. In the proposed method, the duct wall shape is changed under an algorithm based on deformation of a virtual flexible string in flow At each modification step, the difference between current and target wall pressure distributions is applied to the string. The method is an iterative inverse design method and utilizes the analysis code for the flow field solution as a black-box. Some validation test cases and design examples are presented here, which show the robustness and flexibility of the method in handling complex geometries. In cases with separated flow pressure distribution, a unique solution for inverse design problem does not exist. The design algorithm is a physical and quick converging approach and can efficiently utilize commercial flow analysis software.

Inverse design of 2-D subsonic ducts using flexible string algorithm

Abstract: The duct inverse design in fluid flow problems usually involves finding the wall shape associated with a prescribed distribution of wall pressure or velocity. In this investigation, an iterative inverse design method for 2-D subsonic ducts is presented. In the proposed method, the duct walls shape is changed under a novel algorithm based on the deformation of a virtual flexible string in flow. The deformation of the string due to the local flow conditions resulting from changes in wall geometry is observed until the target shape satisfying the prescribed wall's pressure distribution is reached. The flow field at each step is analysed using Euler equations and the advection upstream splitting method method. Some validation test cases and a design example are presented here which show the robustness and flexibility of the method in handling complex geometries. The method is a physical and quick converging approach and can efficiently utilize commercial flow analysis software.

Aerodynamic performance improvement of wind turbine blade by cavity shape optimization

Abstract: Many conventional airfoils, despite a good performance at their design points, get out of optimal conditions outside the design points. One passive way to enhance the airfoil performance is to use a cavity with an optimized shape. In this study, Riso_B1_18 airfoil, having a remarkable aerodynamic performance for wind turbine blades, is selected as a substrate for deploying an optimized cavity on the airfoil. For shape optimization of a cavity, its shape and downstream suction surface are parametrized to reach an optimum lift-to-drag ratio as the target function by using the genetic algorithm. The results of transient numerical solution indicate that the optimized cavity is well capable of draping vortex to control the stall margin, prevent flow fluctuations and significantly increase the lift-to-drag ratio at off-design conditions. To validate the performance improvement obtained from this numerical optimization, a force measurement setup is accomplished in a wind tunnel with 30 × 30 cm2 test section to measure the lift and drag forces of the Riso airfoil with and without optimized cavity. The experimental results shows that the lift-to-drag ratio increases 31% at AOA = 14° and 57% at AOA = 20° due to using the optimized cavity.

Aerodynamic Design of S-Shaped Diffusers Using Ball–Spine Inverse Design Method

Abstract: Recently, an inverse design algorithm called ball-spine algorithm (BSA) is introduced for the design of 2-D ducts. In this approach, the walls are considered as a set of virtual balls that can freely move along the straight directions called spines. In the present work the method is developed for quasi 3-D design of S-shaped ducts with a predefined width. To do so, the upper and lower lines of the S-duct symmetric section are modified under the BSA and then, the 3-D S-duct geometry is obtained based on elliptic cross sectional profiles. The target pressure distributions along the upper and lower lines are prescribed so that the separation does not occur. Finally, the flow through the designed S-duct is numerically analyzed using a viscous flow solver with the SST turbulence model to validate the designed S-duct performance.Copyright © 2014 by ASME

Investigation of a centrifugal compressor and study of the area ratio and TIP clearance effects on performance

Abstract: In this research, the centrifugal compressor of a turbocharger is investigated experimentally and numerically. Performance characteristics of the compressor were obtained experimentally by measurements of rotor speed and flow parameters at the inlet and outlet of the compressor. Three dimensional flow field in the impeller and diffuser was analyzed numerically using a full Navier-Stokes program with SST turbulence model. The performance characteristics of the compressor were obtained numerically, which were then compared with the experimental results. The comparison shows good agreement. Furthermore, the effect of area ratio and tip clearance on the performance parameters and flow field was studied numerically. The impeller area ratio was changed by cutting the impeller exit axial width from an initial value of 4.1 mm to a final value of 5.1 mm, resulting in an area ratio from 0.792 to 0.965. For the rotor with exit axial width of 4.6 mm, performance was investigated for tip clearance of 0.0, 0.5 and 1.0 mm. Results of this simulation at design point showed that the compressor pressure ratio peaked at an area ratio of 0.792 while the efficiency peaked at a higher value of area ratio of 0.878. Also the increment of the tip clearance from 0 to 1 mm resulted in 20 percent efficiency decrease.

Classifications, applications, and design challenges of drones: A review

Abstract: Nowadays, there is a growing need for flying drones with diverse capabilities for both civilian and military applications. There is also a significant interest in the development of novel drones which can autonomously fly in different environments and locations and can perform various missions. In the past decade, the broad spectrum of applications of these drones has received most attention which led to the invention of various types of drones with different sizes and weights. In this review paper, we identify a novel classification of flying drones that ranges from unmanned air vehicles to smart dusts at both ends of this spectrum, with their new defined applications. Design and fabrication challenges of micro drones, existing methods for increasing their endurance, and various navigation and control approaches are discussed in details. Limitations of the existing drones, proposed solutions for the next generation of drones, and recommendations are also presented and discussed.

Damage detection techniques for wind turbine blades: A review

Abstract: Blades play a vital role in wind turbine system performances. However, they are susceptible to damage arising from complex and irregular loading or even cause catastrophic collapse, and they are expensive to maintain. Defects or damages on wind turbine blades (WTBs) not only reduce the lifespan and power generation efficiency of the wind turbine, but also increase monitoring errors, safety risks and maintenance costs. Therefore, damage detection for WTBs is of great importance for failure avoidance, maintenance planning, and operation sustainability of wind turbines. This paper provides a comprehensive review of state-of-the-art damage detection techniques for WTBs, including most of those updated methods based on strain measurement, acoustic emission, ultrasound, vibration, thermography and machine vision. Firstly, typical damages of WTBs are comprehensively introduced. Secondly, detection principles, development methods, pros and cons of the aforementioned techniques for blade inspection, and their fault indicators are reviewed. Finally, potential research directions of WTB damage detection techniques are addressed via a comparative analysis, and conclusions are drawn. It is expected that this review will provide guidelines for practical WTB inspections, as well as research prospects for damage detection techniques.

PSOSCALF: A new hybrid PSO based on Sine Cosine Algorithm and Levy flight for solving optimization problems

Abstract: The development of the meta-heuristic algorithms for solving the optimization problems and constrained engineering problems is one of the topics of interest to researchers in recent years. Particle swarm optimization algorithm (PSO) is one of the social search-based and swarm intelligence algorithms that is distinguished by its high speed, low number of parameters and easy implementation. However, the PSO algorithm has disadvantages such as finding the local minimum instead of the global minimum and debility in global search capability. In this article, in order to solve these deficiencies, the PSO algorithm is combined with position updating equations in Sine Cosine Algorithm (SCA) and the Levy flight approach. Therefore, a new hybrid method called PSOSCALF is introduced in this paper. In the SCA algorithm, the mathematical formulation for the solution updating is based on the behavior of sine and cosine functions. These functions guarantee the exploitation and exploration capabilities. Levy flight is a random walk that produces search steps using Levy distribution and then, with large jumps, more effective searches are occurred in the search space. Thus, using combination of the SCA and Levy flight in the PSOSCALF algorithm, the exploration capability of the original PSO algorithm is enhanced and also, being trapped in the local minimum is prevented. The performance and accuracy of the PSOSCALF method have been examined by 23 benchmark functions of the unimodal and multimodal type and 8 constrained real problems in engineering. The optimization results of the test functions show that the PSOSCALF method is more successful than the PSO family and other algorithms in determining global minimum of these functions. Also, the proposed PSOSCALF algorithm is successfully applied to the real constrained engineering problems and provides better solutions than other methods.

Evolution of space drones for planetary exploration: A review

Abstract: In the past decade, there has been a tendency to design and fabricate drones which can perform planetary exploration. Generally, there are various ways to study space objects, such as the application of telescopes and satellites, launching robots and rovers, and sending astronauts to the targeted solar bodies. However, due to the advantages of drones compared to other approaches in planetary exploration, ample research has been carried out by different space agencies in the world, including NASA to apply drones in other solar bodies. In this review paper, several studies which have been performed on space drones for planetary exploration are consolidated and discussed. Design and fabrication challenges of space drones, existing methods for their flight tests, different methods for deployment and planet entry, and various navigation and control approaches are reviewed and discussed elaborately. Limitations of applying space drones, proposed solutions for future space drones, and recommendations are also presented and discussed.

Aerodynamics of small vehicles

Abstract: In this review we describe the aerodynamic problems that must be addressed in order to design a successful small aerial vehicle. The effects of Reynolds number and aspect ratio (AR) on the design and performance of fixed-wing vehicles are described. The boundary-layer behavior on airfoils is especially important in the design of vehicles in this flight regime. The results of a number of experimental boundary-layer studies, including the influence of laminar separation bubbles, are discussed. Several examples of small unmanned aerial vehicles (UAVs) in this regime are described. Also, a brief survey of analytical models for oscillating and flapping-wing propulsion is presented. These range from the earliest examples where quasi-steady, attached flow is assumed, to those that account for the unsteady shed vortex wake as well as flow separation and aeroelastic behavior of a flapping wing. Experiments that complemented the analysis and led to the design of a successful ornithopter are also described.