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Effect of Cylinder Roughness on Strouhal Number
Yanovych, Vitalii ; Duda, D. ; Uruba, Václav ; Procházka, Pavel P. ; Antoš, Pavel
The main goal of this paper is to establish a better understanding of the relationship between a Strouhal number and surface roughness. Hot-wire anemometry was used to evaluations the characteristics of turbulent flow behind circular cylinders with different relative roughness 0% (smooth surface) 0.83%, 1.67%, 3.33%, and 6.67%. At the experimental investigation, the Reynolds number based on the cylinder diameter was 5 × 103 < Red < 2 × 104. The obtained data showed that the Strouhal number decreased with increasing roughness. While, the dissipation rate decreases, and the value of the Kolmogorov and Taylor microscales increases. Also, spectral analysis of streamwise velocity fluctuations allowed us to estimate the location of the vortex-shedding frequency which at growing roughness tends to reduce.
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Ignitior and power supply system of OSRAM 1000W/D lamp
Zajíček, Antonín ; Šonský, Jiří
The report contains description of power supply and ignitor of high pressure mercury lamp OSRAM HBO 1000W/D. The lamp is utilized during optical measurements of transient flow fields, especifically for interferometry and schlieren photography in the Nový Knín aerodynamic laboratory. The report also contains user manual for the power supply chain.
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Modification of the Algebraic Transition Model for Wall Roughness Effect Including a Rough Strip
Straka, P. ; Příhoda, Jaromír
The contribution deals with the simulation of the laminar/turbulent transition on a rough wall. The algebraic transition model taking into account wall roughness according to Straka and Příhoda [8] was further extended for the effect of short rough strip near the leading edge. The proposed correlation was tested by means of incompressible flow over a flat plate covered by sand paper and around the NACA 0012 airfoil with a rough strip near the leading edge. The agreement with experiments is appropriate nevertheless the applicability of the correlation is limited due to the lack of relevant experimental results.
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Effect of Various Boundary Conditions on the Supersonic Flow Through the Tip-Section Turbine Blade Cascade with a Flat Profile
Musil, Josef ; Příhoda, Jaromír ; Fürst, J.
The paper deals with the numerical simulation of 2D compressible flow though the tip-section turbine blade cascade with a flat profile. The OpenFOAM code was used for simulations based on the Favre-averaged Navier-Stokes equations completed by the two-equation SST turbulence model and the gama-Re_th transition model proposed by Langtry and Menter (2009). Calculations were carried out for two nominal regimes with the inlet Mach number M1 = 1.2 and isentropic outlet Mach numbers M2is = 1.7 and 1.9. Simulations of compressible flow with the supersonic inlet were focused on the relation between of the inlet Mach number and the inlet angle given by the unique incidence rule. Further, the effect of the inlet free-stream turbulence and of the outlet isentropic Mach number on the flow filed in the blade cascade was investigated. Numerical results were compared with results of optical and pressure measurements.
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Flow separation in blade cascades at off-design regimes of operation
Šafařík, Pavel
Particular results from experimental aerodynamic investigation of blade cascades at extreme angle of incidence are presented. Data for modelling of off-design performance of machines are derived from simplified concepts on flow parameters in flow parts of turbomachines. Simulation of these complex conditions in the wind tunnel enables to observe and measure important flow structures and their development. An extensive flow separation is one of significant aerodynamic phenomena at extreme incidence angles of flow into blade cascades. Results of investigation prove considerable increase of coefficient kinetic energy losses at occurrence of flow separation. At high speed flows, transonic instability can set in. Unsteady phenomena are observed namely at extreme flow incidence conditions corresponding to considerable off-design performance of turbomachines.
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