Boundary Layer Control of an Axial Compressor Cascade Using Nonconventional Vortex Generators

Boundary layer control plays a decisive role in controlling the performance of axial compressor. Vortex generators are well known as passive control devices of the boundary layer. In the current study, two nonconventional types of vortex generators are used and their effects are investigated. The used vortex generators are doublet, and wishbone. Three dimensional turbulent compressible flow equations through an axial compressor cascade are numerically simulated. Comparisons between cascade with and without vortex generators are performed to predict the effect of inserting vortex generator in the overall performance of the axial compressor. Results indicate that using vortex generators leads to eliminate or delay the separation on the blade suction surface, as well as the endwall. Furthermore, the effects of the vortex generators and their geometrical parameters on the aerodynamic performance of the cascade are documented. In conclusion, while the investigated vortex generators cause a slight increase in the total pressure loss, a significant reduction in the skin friction coefficient at the bottom endwall is found. This reduction is estimated to be about 46% using doublet and 32% using wishbone.

Airfoil Optimization Using Area-Preserving Free-Form Deformation

Given the importance of structural integrity of aerodynamic shapes, the necessity of including a cross-sectional area equality constraint among other geometrical and aerodynamic ones arises during the optimization process of an airfoil. In this work an airfoil optimization scheme is presented, based on Area-Preserving Free-Form Deformation (AP FFD), which serves as an alternative technique for the fulfillment of a cross-sectional area equality constraint. The AP FFD is based on the idea of solving an area correction problem, where a minimum possible offset is applied on all free-to-move control points of the FFD lattice, subject to the area preservation constraint. Due to the linearity of the area constraint in each axis, the extraction of an inexpensive closed-form solution to the area preservation problem is possible by using Lagrange Multipliers. A parallel Differential Evolution (DE) algorithm serves as the optimizer, assisted by two Artificial Neural Networks as surrogates. The use of multiple surrogate models, in conjunction with the inexpensive solution to the area correction problem, render the optimization process time efficient. The application of the proposed methodology for wind turbine airfoil optimization demonstrates its applicability and effectiveness.

Closed-Form Analytical Solutions for Thin-Walled Cylindrical Composite Shell Structures Subjected to Axial and Bending Loads Under Temperature Environment

This research discourse presents the development of a holistic mathematical model that is dedicated to showcase a set of analytical expressions for predicting global stiffness (axial stiffness, bending stiffness) and a material response characterization based on ply-per-ply in-plane stress investigations relevant to open-celled multidirectional curved cylindrical shell configurations. Additionally, the analytical model is shown to present the capability to mathematically determine the location of the centroid for thin-walled, composite cylindrical shells. The resulting centroidal expression for a composite system is essentially shown to be a primary function of material properties, composite stacking sequence, fiber orientation angle and the structural geometry as opposed to metal counterparts whose centroidal point is solely governed by their geometry. Analytical stress estimates are computed for thin-walled curved cylindrical shell constructions that are subjected to typical tension and longitudinal bending type loading conditions applied at the centroid under the presence and absence of a uniformly distributed thermal loading environment. A broad parametric investigation on the in-plane ply stresses (σx,σy,τxy) are conducted via choosing three fundamental parameters namely; varying mean radius of curvature, changing laminate thickness-to-mean radius ratio and increasing laminate thickness respectively. Three preferentially tailored variabilities in ply stacking sequence are established from a [(±45° / 0°]s symmetric-balanced composite lay-up to illustrate the effects on ply stresses. An ANSYS based finite element analysis scheme is employed to numerically determine the location of centroid and further substantiate the analytically acquired centroid predictions including and excluding the effects of temperature. The centroidal point is identified and its location is progressively reported for a fully open cross-sectioned curved strip to a fully closed cylindrical composite tube configuration by examining their distribution pattern as a function of circumferential arc angle (2α). FE tool is additionally utilized to compare the analytical stiffness predictions and analyze the validity of the in-plane analytical stress estimates. Excellent agreement is achieved in comparison between analytical solutions and computationally generated FE results. The central goal of this work is to demonstrate the potential of the formulated mathematical framework in accurately predicting the key mechanical attributes that dictates the structural behavior of curved composite shell members. This analytical model is designed to serve as a robustly efficient tool towards assisting structural design engineers in quickly gaining a broad fundamental understanding on the physical characteristics and structural response of such configurations by accurately conducting simple parametric studies during preliminary design phase prior to performing complex FE analyses.

Innovative Nose Cone Design of Aircraft

The term aerodynamic design means to have a drag reducing shape that cause to reduce the resistance offered by the fluid. Currently designs of the aircraft nosecone is simple rigid shaped Our concept is to have a type of inter-flight convertible nosecone, which can change its shape according with the physical condition of the environment, it means when the aircraft is to take-off, at that time it must have the most aerodynamic shape. And thus the shape of its nosecone should be sharp or may be pin pointed. And if the aircraft has to land back on the runway, it has to resist the air so that the landing can be much smoother & safer. Thus the shape of the nosecone must be blunt. To make this possible we have an idea of conversion of the nosecone during the flight, To verify our idea and to found its real application, we have done various aerodynamic nosecone analysis for aircraft, for which we have followed various mathematical series like ogive series, hack series, power series and ellipse series to find out the best possible solution. We are aiming for the better nosecone design of aircraft, whose shape will vary with the situation and thus it is possible to increase the efficiency of the aircraft in terms of aerodynamic.

On the Overall Properties of Composites Reinforced by Fibers With Prescribed Orientations

This study is concerned with development of bounds on the elastic properties of fiber reinforced composites with arbitrary orientational distribution of fibers. Generalization of the Mori-Tanaka model [1] and Hashin-Schtrikman variational bounds [2] to the cases of non-aligned composite phases are examined. Orientation distribution functions (ODF) are used to describe orientation probability density. It is shown that the Mori-Tanaka scheme applied to the non-aligned fiber reinforced composites violates symmetry of the effective elastic moduli tensor. The study of the literature also reveals that there are no known bounds derived for the composites with orientational distribution (except for the random uniform distribution) of phases. To overcome this issue we propose to formulate a problem of finding tightest bounds for the composites with non-aligned phases as a nonlinear semidefinite optimization problem, i.e., an optimization problem where the optimization variables are represented by symmetric positive semidefinite matrices. Such a formulation guarantees that any solution of the optimization problem represents a valid tensor of elastic material properties. The optimization problem then is solved by an interior point method to produce optimal bounds for the overall elastic properties of two-phase composite with uniform distribution of carbon nanotubes in a polymer matrix.

Failure Analysis in Hybrid Composite Laminates Using Acoustic Emission and Microscopy

Fiber Reinforced Plastic (FRP) composite materials are widely used in many applications especially in aircraft manufacturing because they offer outstanding strength to weight ratio compared to other materials such as aluminum alloys. The use of hybrid composite materials is potentially an effective cost saving design while maintaining strength and stiffness requirements. In this work, Woven Carbon Fibers (WCFs) along with Unidirectional Glass Fibers (UDGFs) are added to a an aerospace-rated epoxy matrix system to produce a hybrid carbon and glass fibers reinforced plastic composite plates. The manufacturing method used here is a conventional vacuum bagging technique and the stacking sequence achieved consists of a symmetric and balanced laminate (±451WCF, 03UDGF, ±451WCF) to simulate the layup usually adopted for helicopter composite blades constructions. Then, tensile static tests samples are cut according to ASTM standard using a diamond blade and tested using a servohydraulic test machine. Acoustic Emission (AE) piezoelectric sensors (transducers) are attached to the samples surface using a special adhesive. Stress waves that are released at the moments of various failure modes are then recorded by the transducers in the form of AE hits and events (a burst of hits) after they pass through pre-amplifiers. Tests are incrementally paused at load levels that represent significant AE hits activity which usually corresponds to certain failure modes. The unbroken samples are then thoroughly investigated using a high resolution microscopy. The multi load level test-and-inspect method combined with AE and microscopy techniques is considered here to be an innovation in the area of composite failure analysis and damage characterization as it has not been carried out before. Results are found to show good correlation between AE hits concentration zones and the specimens damage location observed by microscopy. Waveform analysis is also carried out to classify the damage type based on the AE signal strength energy, frequency and amplitude. Most of the AE activity is found to initiate from early matrix cracking that develops into delamination. Whereas little fiber failure activity has been observed at the initial stages of the load curve. The results of this work are expected to clear the conflicting reports reported in the literature regarding the correlation of AE hits characteristics (e.g. amplitude level) with damage type in FRP composite materials. In addition, the use of a hybrid design is qualitatively assessed here using AE and microscopy techniques for potential cost savings purposes without jeopardizing the weight and strength requirements as is the case in a typical aircraft composite structural design.

Experimental Investigation on the Transcritical Behaviour of Methane and Numerical Rebuilding Activity in the Frame of the HYPROB-BREAD Project

The HYPROB Program, led by the Italian Aerospace Research Centre, has the aim to increase the Italian capabilities in the design and manufacture of liquid oxygen-methane rocket engines; in particular, the line, named HYPROB-BREAD, has the final goal of developing and testing a ground demonstrator of three-tons-thrust class, regeneratively cooled by liquid methane. Some intermediate breadboards have been conceived, realized and tested to deepen some technical issues: among them a specific breadboard, named MTP-B (Methane Thermal Properties Breadboard), has been designed and tested to investigate thermal characteristics of methane as a coolant, and perform the design validation activity by collecting experimental data. The concept is based on the electrical heating of a conductive material that transfers a thermal load, similar to those experienced in the regenerative cooling chambers, to a channel, having dimensions typical of regenerative cooling jackets. The test campaign has been successfully accomplished by collecting data, in terms of inlet/outlet fluid temperature and pressure, temperature at different stations and depth from the channel bottom surface. A numerical rebuilding activity has been planned to verify the numerical thermal models and engineering tools, adopted for the design of the final demonstrator. Thus, simulations on a fully 3-D model, including inlet and outlet interfaces, were performed on some test conditions after completing a preliminary activity on cold flow tests. The results of the numerical rebuilding are satisfactory since very good comparisons with the experimental data were observed.

Numerical Analysis of Design Parameters With Strong Influence on the Aerodynamic Efficiency of a Small-Scale Self-Pitch VAWT

In the paper, four key design parameters with a strong influence on the performance of a small-scale high solidity variable pitch VAWT (Vertical Axis Wind Turbine), operating at low tip-speed-ratio (TSR) are addressed. To this aim a numerical approach, based on a finite-volume discretization of two-dimensional Unsteady RANS equations on a multiple sliding mesh, is proposed and validated against experimental data. The self-pitch VAWT design is based on a straight blade Darrieus wind turbine with blades that are allowed to pitch around a feathering axis, which is also parallel to the axis of rotation. The pitch angle amplitude and periodic variation are dynamically controlled by a four-bar-linkage system. We only consider the efficiency at low and intermediate TSR, therefore the pitch amplitude is chosen to be a sinusoidal function with a considerable amplitude. The results of this parametric analysis will contribute to define the guidelines for building a full size prototype of a small scale turbine of increased efficiency.

Accelerating RBF-Based Mesh Deformation by Implementing an Agglomeration Strategy

During the past decade Radial Basis Functions-based mesh deformation techniques have been emerged as an indispensable tool of numerical simulations entailing grid transformation. Despite their important contribution to such problems, they suffer from a significant drawback; they call for relatively excessive memory and computation time requirements. A remedy to this deficiency seems to be the selection of a reduced set of surface nodes, to be used as RBF’s centers; an equations’ system with decreased dimensions is obtained in that way. In this paper a new methodology for such a reduced surface point selection is proposed, considering agglomeration of surface nodes’ control volumes. It relies on the strategy followed by the corresponding multigrid methods aiming to accelerate numerical solutions of fluid flow, radiative heat transfer, etc., problems. The developed merging procedure resembles the advancing front technique, as it begins from regions with surface discontinuities extending successively to the rest of the boundary domain. The proposed algorithm is assessed against a test case considering parabolic deformation of the wing of the DLR-F6 aircraft model; its potential to effectively generate deformed grids in terms of accuracy and efficiency is demonstrated, despite the notable reduction of RBF’s centers.