INCORPORATION OF FORWARD BLADE SWEEP IN THE NON-FREE VORTEX DESIGN METHOD OF AXIAL FLOW TURBOMACHINERY ROTORS

The paper presents a novel strategy for design of high-performance non-free vortex axial flow rotors with forward swept blades. The design methodology incorporates the determination of an optimum extent of forward blade sweep into the non-free vortex design methodology, considering the realistic three-dimensional blade-to-blade flow. The design methodology is to be completed with Computational Fluid Dynamics analysis and global measurements on the turbomachinery unit. A fan rotor design example is presented

Fourier Analysis of Beamforming Data at the Tip of an Axial Fan Rotor

Axial fans operate in large numbers, often in the close vicinity of humans, therefore reducing their noise is a primary concern. In this paper, beamforming is applied to get information about the location and strength of noise sources on the rotor. This information is invaluable, however, difficult to interpret because of some limitations of the beamforming method. The broadband noise radiated in the upstream direction by an axial fan rotor has been examined by means of a phased array microphone system, and the recorded data have been processed with the use of the Rotating Source Identifier beamforming algorithm. In order to reduce the complexity of the source maps, spatial Fourier analysis has been applied to the beamforming-based circumferential source strength distribution taken at the tip radius of the rotor, where the complexity of the local aerodynamic phenomena makes the evaluation of the aeroacoustic noise source data especially challenging. As part of the processing method, a criterion has been introduced for identifying the significant components of the noise sources. The Fourier analysis enabled the effective enhancement of distinct noise sources out of the beamforming database, despite the presence of signal perturbations and limitations. The noise sources have been located and quantified with use of the Fourier transformation and with help of a criterion based on the physical properties of the noise generation mechanisms

Parameter Study of a Loss Reducing Passive Flow Control Method in a Square-to-square Sudden Expansion

The energy consumption of mechanical ventilation in buildings needs to be reduced. An efficient way to achieve this goal is to reduce the hydraulic resistance of the ventilation duct system elements, for example, that of sudden expansions. Ventilation ducts and pipe fittings are frequently of rectangular cross-section. The present paper investigates a passive flow control method in order to reduce the loss coefficient of a square-to-square sudden expansion, where the loss-reducing appendages are short guide vanes, termed as miniflaps, placed at the step edge of the sudden expansion. The turbulent flow is examined numerically using the generalized k-ω model of the Ansys Fluent software for different area ratios of the sudden expansion, miniflap lengths, and miniflap angle setups. The Reynolds number is kept constant at 1.08·105. Based on the results of the numerical simulations, the loss coefficient of the sudden expansion can be reduced by ~20–25% for an optimum miniflap angle between 9° and 12°. Increasing the length of the miniflaps leads to a greater reduction of the loss coefficient up to a miniflap length of 0.3 dh1, where dh1 is the upstream hydraulic diameter of the duct

A SEMI-EMPIRICAL MODEL FOR CHARACTERISATION OF FLOW COEFFICIENT FOR PNEUMATIC SOLENOID VALVES

A semi-empirical model has been elaborated for analyzing and predicting the flow characteristics of small electro-pneumatic (EP) valves within a wide range of pressure ratio. As a basis for characterization of flow coefficient, an analytical model has been established for a simplified geometry. This model has been corrected corresponding to more complex valve geometries, utilizing the results of axisymmetric quasi-3D (Q3D) computations using the Computational Fluid Dynamics (CFD) code FLUENT. By this means, a semi-empirical modelling methodology has been elaborated for characterization of through-flow behavior of pneumatic valves of various geometries

Establishment of a Beamforming Dataset on Basic Models of Low-Speed Axial Fan Blade Sections

The paper presents wind tunnel experiments, supplemented with phased array microphone measurements, on 2D basic models of low-speed axial fan blade sections: a flat plate, a cambered plate, and a RAF6-E airfoil. It aims at documenting the establishment of an acoustic beamforming dataset for the three profiles. The phased array microphone measurements offer spatially resolved information on the generated noise. The measurement setup enables the correlation of the streamwise evolution of the blade boundary layer with the associated noise characteristics. The dataset incorporates a wide range of incidence and Reynolds-numbers investigated. The present paper is confined to reporting on experimental results for arbitrarily selected representative incidences, Reynolds numbers, frequency bands, and profiles. The paper outlines a methodology for the evaluation and representation of the beamforming data in the following forms: source strength level based third-octave spectra obtained using background noise subtraction; maps presenting the loci of source strength level maxima; noise source maps for frequency bands of anticipated vortex shedding noise

Aerodynamic study on straight, arc-swept and twisted stationary linear cascade blades

A computational investigation has been carried out on the effects of sweep and twist in stationary linear cascades. Circular arc sweep has been applied to the datum cascade of straight cylindrical blades, i.e. spanwise constant stacking line curvature was prescribed. Positive sweep was applied near the endwalls, and the sweep angle distribution was symmetrical to the midspan plane. The straight and the arc-swept blades were studied at low, near-design, and high incidence angles of the straight blading. Twisted versions of the straight and the arc-swept blades were studied for spanwise constant inlet flow angle. The studies demonstrated the benefits of circular arc sweep for both untwisted and twisted blade rows, such as local loss reduction and uniformisation of cascade outlet axial velocity profile. Blade twist was found favourable from the aspect of endwall separation zone reduction

VALIDATION OF A COMPUTATIONAL FLUID DYNAMICS METHOD TO BE APPLIED TO LINEAR CASCADES OF TWISTED-SWEPT BLADES

A synthetic method has been elaborated for the validation of a Computational Fluid Dynamics tool developed for the future investigation of the combined aerodynamic effects of sweep and spanwise changing stagger angle on stationary linear blade cascades. The validation method is based on specially selected experimental data available in the open technical literature. The capabilities of the CFD method for resolution of near-endwall phenomena due to sweep as well as of the effect of changing incidence were tested. The CFD methodology and the experimental validation process have been documented herein in accordance with the requirements regarding industrial CFD tools

BASALT FIBER AS A REINFORCEMENT OF POLYMER COMPOSITES

The applicability of basalt fibers as reinforcing materials has been examined in a polypropylene (PP) matrix. The brittle basalt fibers have been mixed with the PP fibers by carding combined with needle punching and the composite sheets have been produced by pressing. SEN-T fracture mechanical specimens have been cut out of the sheets and the sensitivity to crack propagation has been examined in the composites. It has been proven that fracture toughness increases as a result of reinforcing. The toughness of the composite increased compared to the matrix due to the gravels appeared at the end of basalt fibers. It has been pointed out that the gravels are results of the Junkers production technology. The observations have also been proven by electron microscopic images. A model has been outlined for investigation of influence of change of technological parameters on basalt fiber production