Fast-response probes in multistage turbomachinery are typically used to measure unsteady flows and turbulence in a number of traverse locations throughout the machine (rotor-stator interregions, inlet and outlet sections, tip clearance gaps…). When used intensively, they provide complete information of time-resolved flow structures, including wake patterns, wake mixing, wake-wake and rotor-wake interactions or turbulence transport in 2D planes and even 3D pictures if the raw signals are post-processed accurately. The segregation between deterministic, unsteady features and turbulent scales is essential to understand the unsteady mechanisms responsible for the energy transfer and requires an accurate selection of the sampling frequencies and the total length of the measured traces to assure a valid statistical reduction. Similar considerations must be made if they are filtered in a frequency basis (for example, filtering low-scale turbulence or extracting only BPF components), employing welldesigned periodograms or power spectra with minimum scatter and large periods of time integration. This work presents the effect of number of periods (ensembles), resolution in which the averaged periods are reconstructed and turbulence intensity on the experimental accuracy of ensemble-averaged measurements in low-speed axial fans using fast-response probes. In particular, the statistical analysis is established in terms of convergence (residuals) between timeresolved traces retrieved using different sampling frequencies and number of total samples. The possible effects of three-dimensionality, the measured regions (hub, tip, midspan) or the sensibility to turbulence levels is also explored. A technique to quantify the convergence of the phase-locked averaging (PLA) processes is applied to a low-speed axial fan, with twin configurations of rotor-stator and stator-rotor arrangements. As a starting point, a concise survey of usual practices employed by other authors in the literature for axial fans and compressors is firstly reviewed, in order to identify fundamental parameters and values typically adopted to guarantee convergence. Finally, typical requirements are given as a function of the variable analyzed, the wake pattern to be described or the global disorder of the flow structures inside axial flow fans.

A novel design for a contraction nozzle, based on a logarithmic profile, is presented and developed to enhance aerodynamic measurements in a low-speed wind tunnel. The improvements obtained with this new proposal are validated, both, numerical and experimentally. As a starting point, four different wind tunnel contraction profiles are firstly considered and tested using the Computational Fluid Dynamics (CFD) package ANSYS FLUENT®. Both polynomial, due to its classical inclusion for wind tunnels, and logarithmic profiles, due to its expected enhancement, have been studied in terms of avoidance of separation of the boundary layer, procurement of a maximum level of exit-flow uniformity, and minimum turbulence levels at the outlet. Numerical comparison between obtained results shows the benefits of the new logarithmic profile developed by the authors, which was finally employed to construct the nozzle. To characterize its real performance, intensive experimental measurements have been conducted using pressure transducers and both single and dual hot wire anemometry. The pressure coefficient along the nozzle sidewall reveals an optimal evolution, matching perfectly with the theoretical design. In addition, low levels of turbulence and high flow uniformity is confirmed at the nozzle discharge. Turbulence intensities below 0.7% are obtained for the whole range of velocities available in the wind tunnel, and even practically constant uniform flow is obtained for all the traverses tested for validation. These indicators conclude that the contraction designed with the new profile is a good enhancing of the wind tunnel benefits.

Abstract-The scattering properties of dielectric waveguides connected in cascade can be obtained by using the generalized scattering matrix concept, together with the generalized telegraphist equations formulism and the modal matching technique. This review aims to show the potential of periodic structures in dielectric waveguides in order to gain control of light in the design of microwave and photonic devices. The new inverted Π dielectric waveguide is presented. Numerical and experimental results of the complex scattering coefficients were obtained at microwave frequencies. At optical frequencies, results for planar waveguide photonic crystals are included and compared with the numerical values from commercial software. In all cases the agreement was excellent. Electromagnetic and photonic band gaps, photonic windows, optical switching, optical resonant microcavities as well as refractive index optical sensors can be achieved by means of dielectric waveguides in cascade.

Abstract-In this work, we demonstrate that the LSM and LSE modes formulation is an excellent theoretical tool for determining the refractive index and thickness of the guiding layer in planar optical waveguides with step refractive index profile. Refractive index of transparent materials capable of being deposited as a solid thin layer on a substrate for confining light can be evaluated very accurately. The method can be applied to analyze and design monomode and multimode optical waveguides, unlike the methods proposed so far, including cutoff wavelength region. This wave model only requires the experimental evaluation of the effective indices of the guided modes. In order to verify the developed formulation, the commercial software Olympios was used for theoretical comparison. Polymeric planar optical waveguides were fabricated and characterized. A prism coupling method and the Metricon system were used for effective indices measurements and to compare the accuracy. The experimental evaluation of the thickness was carried out by profilometry. In all cases a complete agreement was obtained for refractive index and thickness between theory and experiments.

Fast-response probes in multistage turbomachinery are typically used to measure unsteady flows and turbulence in a number of traverse locations throughout the machine (rotor-stator inter-regions, inlet and outlet sections, tip clearance gaps…). When used intensively, they provide complete information of time-resolved flow structures, including wake patterns, wake mixing, wake-wake and rotor-wake interactions or turbulence transport in 2D planes and even 3D pictures if the raw signals are post-processed accurately. The segregation between deterministic, unsteady features and turbulent scales is essential to understand the unsteady mechanisms responsible for the energy transfer and requires an accurate selection of the sampling frequencies and the total length of the measured traces to assure a valid statistical reduction. Similar considerations must be made if they are filtered in a frequency basis (for example, filtering low-scale turbulence or extracting only BPF components), employing well-designed periodograms or power spectra with minimum scatter and large periods of time integration. This work presents the general guidelines that any statistical procedure must follow to assure that phase-locked averaging results are consistent when applied to velocity signals in multistage turbomachinery. The procedure is established in terms of convergence (residuals) and coherence (error) between time-resolved traces retrieved using different sampling frequencies and number of total samples. The possible effects of three-dimensionality, the measured regions (hub, tip, midspan) or the sensibility to turbulence levels is also explored. The proposed methodology is applied to a low-speed axial fan, so a concise survey of usual practices employed by other authors in the literature is firstly reviewed, in order to identify fundamental parameters and values typically adopted to guarantee convergence. Finally, recommendations are made as a function of the variable analysed, the wake pattern to be described or the global disorder of the flow structures inside axial flow fans.