Axisymmetric synthetic jet actuators making use of loudspeakers and four lengths of the orifice with and without a confinement plate were experimentally tested and compared. The first (reference) orifice was the shortest one and was confined by the actuator wall. The next length of orifices was obtained with the use of one of three orifices’ extension, with or without a confinement plate. The possibility of the use of the power factor to find the first characteristic frequency is presented. The dependence of the reaction force from the orifice length and the power is described. The time-reaction force of the actuator was measured. The actuators with a confinement plate at the time of measurements of frequency function and at the constant power generate less reaction force, as well as less velocity and efficiency, than the ones without it (even 1.8% at the characteristic frequency).

Diffusion of a passive impurity in a random velocity field E V Teodorovich Laser Doppler visualisation of the velocity field by excluding the influence of multiparticle scattering

The dimensional analysis and the numerical parametric study of the typical outer air seal from a low-pressure turbine were performed in the framework of the presented paper. The most crucial variables for the flow through the outer air seal were identified and further dimensionless numbers were derived. The dependent quantities resulting from the analysis were: the axial Reynolds number (formulated with the bulk velocity, corresponding to the mass flow through the seal), the outlet swirl ratio (incorporating the exit flow angle, important for mixing) and the windage heating (related to the internal losses). Additionally, the discharge coefficient was cross-checked enabling further comparison with the available literature. The comprehensive numerical parametric study included all important contributors for the flow through the seal with a parameter operating range appropriate for engine outer air seals.

This paper aims to provide a robust design approach for HAWTs operating in shear flow. This study fills a critical research gap by integrating BEM and vortex theories for blade design in non‐homogeneous inflow conditions. In a modern society, the use of different types of energy is a prerequisite for most human activities. Wind energy, as a renewable energy source, is the fastest‐growing source of energy generation through wind turbines. Such a wind energy conversion system is both economical and environmentally friendly. This requires an understanding of the wind conditions at the site under study. The power of a wind turbine depends on several parameters, including the wind profile and the blade geometry. In the paper, an original method for designing horizontal‐axis wind turbines under non‐uniform inflow conditions is presented. The authors of the paper made an effort to develop and test an experimentally unsophisticated model of a turbine working in shear flow, and to test it in a wind tunnel under conditions simulating real‐world shear flow. The applied theoretical model is implemented in the design problem based on the local momentum theorem and employs some results of the vortex theory of a propeller. The turbine model was designed for wind tunnel conditions to minimize the effect of scale. The desired velocity profile in the tunnel was obtained using a wire mesh system. The data was approximated by fitting curves and then used in design calculations. The tests were conducted under two flow conditions: a nearly uniform flow generated without screens at the outlet of the contraction and a shear flow, with a velocity profile generated by four screens partially covering the outlet of the contraction. Excellent comparability was obtained between the computational model and the experimental results.