Multiple Circular Arc Research Articles

Open NASA Blade Models for Nonlinear Dynamics Simulations

Abstract This contribution presents a catalogue of open turbomachinery blade models dedicated to nonlinear dynamics simulations. Based on a specifically developed in-house computer code, three-dimensional computer-aided design (CAD) models and finite element (FE) models of multiple-circular-arc (MCA) NASA airfoils are generated. Both the in-house code and the models are made freely accessible online. To cover a wide range of geometries, 39 blades are considered from different stages and with different aspect ratios. It is expected that this blade catalogue will provide an opportunity for the direct comparison of recently developed methodologies relative to nonlinear vibration phenomena in turbomachines, including rubbing events and blade-tip/casing contacts. To this end, the paper also contains original results for some of the most emblematic NASA blades, with an emphasis on nonlinear interaction maps and a detailed presentation of redesign operations to mitigate high amplitude of vibrations when blade-tip/casing contacts occur.

Optimal Design and Analysis of a High-Load Supersonic Compressor Based on a Surrogate Model

To explore the internal flow mechanism and improve the performance of a supersonic compressor, an efficient global optimization design method was developed for an axial flow compressor and applied in the optimization design of a prototype supersonic compressor. Based on the multiple circular arc (MCA) blade parameters, the method can be used to parameterize the elementary stage of the blade. The optimized solution is obtained by changing the elementary stage and stacking lines of the blade during the optimization process. It has the advantages of fewer optimization variables, strong physical intuition, and a smooth surface. The optimization results show that a change in the rotor blade shape parameters has a significant effect on the compressor efficiency under design conditions, while a change in the skewed-swept parameters of the stator is the main factor that improves the compressor’s performance under near-stall conditions. Further numerical results show that the optimized rotor changes the form of the shock, weakens the degree of shock boundary layer interference, inhibits the radial migration flow of the supersonic rotor, reduces the loss of the rotor blade top, and improves the performance of the compressor under design conditions. The stator’s optimization restrains the generation of a concentrated shedding vortex at the root of the blades and greatly improves the stall margin of the compressor. Finally, the total pressure ratio and flow rate are less than 1% of the values based on the prototype operating conditions, the design mass flow of the optimized high-load supersonic compressor is increased by 0.25%, the isentropic efficiency is increased by 1.05%, and the stall margin is enhanced by 3.5%, thus verifying the effectiveness of the optimization method.

Ductile failure analysis of epoxy resin plates containing multiple circular arc cracks by means of the equivalent material concept

Ductile failure of polymeric samples weakened by circular arc cracks is studied theoretically and experimentally in this research. Various arrangements of cracks with different arc angles are considered in the specimens such that crack tips experienced the mixed mode I/II loading conditions. Fracture tests are conducted on the multi-cracked specimens and their fracture loads are achieved. To provide the results, the equivalent material concept (EMC) is used in conjunction of dislocation method and a brittle fracture criterion such that there is no necessity for performing complex and time-consuming elastic-plastic damage analyses. Theoretical and experimental stress intensity factors are computed and compared with each other by employing the fracture curves which demonstrate the appropriate efficiency of proposed method to predict the tests results.

Global Optimization of Savonius-Type Vertical Axis Wind Turbine with Multiple Circular-Arc Blades Using Validated 3D CFD Model

Global Optimization of Savonius-Type Vertical Axis Wind Turbine with Multiple Circular-Arc Blades Using Validated 3D CFD Model

Performance Characteristic Modeling for 2D Compressor Cascades

Abstract The flow field in a compressor cascade is very complex owing to the highly 3D, turbulent, and viscous properties. However, in the through-flow analysis method, the viscosity effects are taken into account using empirical models. These models were based on experimental results for early blades. However, the blade types in modern compressors are quite different from those in older compressors. Therefore, it is not possible to predict the performance of modern compressors using the old empirical models. In this study, several multiple circular-arc (MCA) blades commonly used in modern compressors were simulated. After the simulations, a database of the cascade performance was built. Based on this database, some new models were established to predict the performance of modern cascades using regression analysis methods and an artificial neural network (ANN) method. The accuracy of all these new models is high enough for use in engineering applications.

A boundary element analysis for stress intensity factors of multiple circular arc cracks in a plane elasticity plate

In this paper, a numerical approach for analyzing interacting multiple cracks in infinite linear elastic media is presented. By extending Bueckner’s principle suited for a crack to a general system containing multiple interacting cracks, the original problem is divided into a homogeneous problem (the one without cracks) subjected to remote loads and a multiple crack problem in an unloaded body with applied tractions on the crack surfaces. Thus, the results in terms of the stress intensity factors (SIFs) can be obtained by considering the latter problem, which is analyzed easily by means of the displacement discontinuity method with crack-tip elements proposed recently by the author. Test examples are given to illustrate that the numerical approach is very accurate for analyzing interacting multiple cracks in an infinite linear elastic media under remote uniform stresses. In addition, the displacement discontinuity method with crack-tip elements is used to analyze a multiple crack problem in a finite plate. It is found that the boundary element method is also very accurate for investigating interacting multiple cracks in a finite plate. Specially, a generalization of Bueckner’s principle and the displacement discontinuity method with crack-tip elements are used to analyze multiple circular arc crack problems in infinite plate in tension (including: Two Collinear Circular Arc Cracks, Three Collinear Circular Arc Cracks, Two Parallel Circular Arc Cracks, Three Parallel Circular Arc Cracks and Two Circular Arc Cracks) in a plane elasticity plate. Many results are given.

Fredholm integral equation for the multiple circular arc crack problem in plane elasticity

An elementary solution for the multiple circular arc problem is obtained in this paper. The elementary solution is defined as a particular case of the single circular arc crack problem, in which remote stresses are equal to zero, and two pairs of concentrated forces are applied at a prescribed point of crack face. By using the principle of superposition, Fredholm integral equation for the multiple circular arc problem in plane elasticity is obtained. The suggested approach is illustrated by several numerical examples. If a smaller arc crack is surrounded by a larger arc crack, the stress intensity factors for the former become rather small. The phenomenon of shielding is illustrated by examples.

Two-Dimensional Cascade Tests of MCA Blades in the High Transonic Mach Number Region. 5th Report. Effect of Space/Chord Ratio on the Parameters of Cascade Performance. (2).

We carried out 2-D cascade tests of multiple-circular-arc (MCA) blades with a relatively high camber angle of 56 deg. in the region of inlet Mach number (M1) 0.4≤M1≤1.2, and with systematic variations of cascade geometry and incidence angle. Systematic data with respect to inlet Mach number characteristics of the cascade of MCA blades were obtained. We discsussed the effect of space/chord ratio on the performance of cascade of MCA blades, i. e. inlet Mach number characteristics, the relationship between incidence angle and parameters of cascade performance (incidence angle characteristics), in the constant stagger angle of 10°in the 4th report. In the present report, the following items are discussed on the basis of experimental results in the constant stagger angle of 5deg : 1. the effect of space/chord ratio on inlet Mach number characteristics ; 2. the effect of space/chord ratio on the relationship between incidence angle and parameters of cascade performance (incidence angle characteristics) at M1=0.9, 1.0, 1.1 ; 3. the effect of space/chord ratio on stall incidence angle, and reference incidence angle ; 4. the relationship between incidence angle and critical inlet Mach number in the set of space/chomd ratio of 0.4, 0.6, 0.8 ; 5. the optimal incidence angle and the effective working range of incidence angle which was deduced from the above mentioned relationship of (4) ; 6. relationship between space/chord ratio and deviation angle at optimal incidence angle.

Two-dimensional cascade tests of MCA blades in the high transonic Mach number region. 2nd report, On the effect of stagger angle on inlet Mach number characteristics.

We carried out 2-D cascade tests of multiple-circular-arc (MCA) blades with a relatively high camber angle of 56 deg. In the region of inlet Mach number (M1) 0.4 ≤ M1 ≤ 1.2 and with the systematic variations of cascade geometry and incidence angle. Systematic data with respect to inlet Mach number characteristics of the cascade of MCA blades were obtained. An outline of the tests was given in the first report. In the present report, we discuss the following items on the basis of experimental results: 1. the effect of stagger angle on inlet Mach number characteristics. 2. the relation between stagger angle and critical inlet Mach number. 3. the relation between inlet Mach number and superior limit in the available range of operation of stagger angle. 4. the relation between diffusion factor and static pressure rise coeffcient.

Two-dimensional cascade tests of MCA blades in the high transonic March number region. 1st report. An outline of the tests.

We carried out 2-D cascade tests of multiple-circular-arc (MCA) blades with a relatively high camber angle of 56 deg. in the region of inlet Mach number (M1) 0.4 ≤ M1 ≤ 1.2, and with systematic variations of cascade geometry and incidence angle. Systematic data with respect to inlet Mach number characteristics of the cascade of MCA blades were obtained. The present report is chiefly concerned with a few remarks on the method of 2-D cascade tests which invo1ve the following: (1) the details of the blade shape tested, (2) the layout of the cascade tunnel, (3) data critiques on the degree of two-dimensionality, (4) the consideration regarding the effect of axial-velocity-density-ratio on the cascade performance parameters. Inlet Mach number characteristics in the region of minimum incidence angle are discussed.

Two-dimensional cascade tests of MCA blades in the high transonic mach number region. 3rd report. Effect of inlet Mach number on the relation between incidence angle and parameters of cascade performance.

We carried out 2-D cascade tests of multiple-circular-arc (MCA) blades with a relatively high camber angle of 56 deg. in the region of inlet Mach number(M1) 0.4≤M1≤1.2, and with systematic variations of cascade geometry and incidence angle. Systematic data with respect to inlet Mach number characteristics of the cascade of MCA blades were obtained. The effect of stagger angle on inlet Mach number characteristics was discussed in the second report. In the present report, we discuss the following on the basis of experimental results. 1. the effect of inlet Mach number on the relation ship between incidence angle and parameters of cascade performance (incidence-angle characteristics). 2. the effect of stagger angle on incidence angle characteristics. 3. the relation ship between incidence angle and critical inlet Mach number. 4. the relation ship between stagger angle and stall incidence angle, reference incidence angle. 5. the relation ship between limit in the available range of operation of the incidence angle and inlet Mach number.

Optical properties of an inflatable concentrator with parallel fin absorber

Optical properties are investigated for an inflatable, multiple circular arc concentrator which approximates the shape of the CPC with an endosed parallel fin receiver. Some of the structural considerations for fabrication of such a concentrator also are discussed.