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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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Aeroacoustic Noise Source Investigation in the Case of the Blade Cascade
Procházka, Pavel P. ; Antoš, Pavel ; Šnábl, Pavel
The blade cascade consisted of five NACA 0010 profiles is examined in the framework of project dealing with nonlinear dynamic phenomenon related to stall flutter of flexible profiles with pitch degree of freedom in subsonic flow. Various angles of attack (AoA) of the cascade generates different (broadband) aeroacoustic noise. The goal of this article is to describe the existence of possible noise sources using two experimental methods – Particle Image velocimetry (PIV) and hot-wire (HW) anemometry.
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Effect of oscillating blade on tonal noise of blade cascade with five NACA 0010 profiles
Šnábl, Pavel ; Pešek, Luděk ; Radolf, Vojtěch ; Antoš, Pavel ; Procházka, Pavel P. ; Prasad, Chandra Shekhar
The airfoil tonal noise is a well known phenomenon which appears on single airfoils in moderate Reynolds numbers at low angles of attack. It can appear on small aircrafts, fans, wind turbines etc. In thispaper, it was observed on a blade cascade consisting of five NACA 0010 profiles placed in a closed rectangular channel with hard walls when for given conditions, i.e. flow velocity and angle of attack, the cascade tunes to one single frequency. During the middle blade oscillation, the single tone splits up to several tones with lower intensity modulated by the excitation frequency. Thus, the oscillation of one blade suppresses the tonal noise generation in the cascade.
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Intermitence factor evaluation by bypass boundary layer transition in flows on rough surface on flat plate
Skála, Vladislav ; Antoš, Pavel
Bypass boundary layer transition in flows on rough surface on flat plate was investigated experimentally. It was measuered cases with combination of roughness of surface by different free stream turbulence intenzity. Hot wire anemometry technique was used. Measuerement were made on flat plate in closed wind tunnel. Flat plate was covered by different roughness foils (sandpapers). Adverse pressure gradient was set by diffuser in tested section of wind tunnel. Grid turbulence of free stream was controlled by grid. Hot wire anemometry technique was used, intermitency factor was evaluated.
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Development of Boundary Layer on a Heated Flat Plate
Antoš, Pavel ; Kuznetsov, Sergeii
An experimental study of boundary layer on a flat plate with heat transfer was done. Temperature and velocity boundary layer development was studied on a uniformly heated flat plate with zero pressure gradient by means of hot-wire anemometry. Several levels of heat flux at the wall were used. The difference between the wall temperature and free-stream temperature was set up to 180 K. Measurements were performed in the closed-circuit wind tunnel with zero pressure gradient at free-stream velocity of 3-5 m/s and turbulence intensity of 0.8 percent. The velocity and the temperature profiles of mean values and fluctuations are presented.
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A comment on the flat plate leading edge shape on laminar-turbulent transition
Antoš, Pavel ; Jonáš, Pavel ; Procházka, Pavel P.
Laminar-turbulent transition region is investigated in zero pressure gradient boundary layers developing on flat plates with different shapes of leading edges namely with the elliptical profile; the superelliptical one and with the thin circle profile. The mean flow field characteristics are presented and discussed. Near downstream from the leading edge are mean velocity profiles very similar to the Blasius solution in all compared configurations. The dramatic effect of the leading edge is ascertained in the beginning of the skin friction coefficient deflection from the course after Blasius solution. The start of deflection is moving downstream in sequence: elliptic – super-elliptic – circle shape. The length of the transitional region shortens in the opposed sequence.
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