|
| |
|
|
Frekvenční charakteristika generátoru anulárního syntetizovaného proudu s velkým vnitřním průměrem
Krejčí, A. Petr ; Trávníček, Zdeněk ; Tesař, Václav ; Kordík, Jozef ; Pavelka, Miroslav
An annular synthetic jet actuator of large inner/outer diameter ratio of the nozzle has been developed, and four variants were designed, manufactured, and tested. The resonance frequency was estimated theoretically, based on the mechanical energy balance, and then measured by the pneumometric method. The resultant value was found to be 40 Hz. The nozzle geometry effect on the resonance frequency and on the velocity was quantified; both effects were concluded to be surprisingly small, less than 5%.
|
|
|
Numerická simulace Kármánovy vírové řady za izotermických i neizotermických podmínek
Šponiar, D. ; Trávníček, Zdeněk ; Vogel, J.
This report deals with numerical simulation of the wake airflow behind a circular cylinder using FLUENT solver. The flow is assumed to be two–dimensional, laminar, and incompressible. The Reynolds number ranges Re = 30:-170. The isothermal numerical simulation agree very well with experimental data except the situation near the critical stage (between the steady and vortex shedding regimes); the maximum deviations of simulation and experiments are within 1.2%. The results obtained under the non-isothermal conditions are quite good – except the simulation near the critical stage, where the problems are similar as in the isothermal case.
|
|
| |
|
|
Numerical simulation of the von Kármán vortex street
Šponiar, D. ; Trávníček, Zdeněk ; Vogel, Jiří
This report deals with numerical simulation of the wake airflow behind a circular cylinder using FLUENT solver. The flow is assumed to be two–dimensional, laminar, isothermal, and incompressible. The Reynolds number ranges Re = 30÷170. The computations give the steady wake flow for Re = 30÷60 and the periodic vortex shedding (von Kármán vortex street) for Re = 60÷170. The vortex shedding frequency has been quantified in the term of the Strouhal number–Reynolds number relationship. The present results agree very well with the previous experimental data, the maximum deviations of the simulations and experiments are within 1.2%.
|
|
|
Piezokeramický generátor pro syntetizovaný proud
Dančová, P. ; Vít, T. ; Trávníček, Zdeněk
Synthetic jets are jets of fluid which are generated by periodic pulzations of fluid. The pulsation generator can work on principle of loudspeaker, piston, pieocrystal or the other equipment. In our experiments, the actuator works on piezoceramic transducer (PTC). The paper shows results of vibrometry principle and results of FEM simulations.
|
|
| |
|
|
Termoakustika
Trávníček, Zdeněk
The thermoacoustic energy conversion systems can operate as heat pumps (or refrigerators which are based on the same principle) or prime movers. The design optimization of the thermoacoustic refrigerator was made using two methods, namely the optimization based on the cooling load maximization and on the coefficient of performance (COP) maximization. The highest COP can be achieved with the noble gas mixture helium-xenon (62%-38%) as the working fluid, while the highest cooling load can be achieved with pure helium.
|
|
|
Syntetizovaný proud
Dančová, P. ; Trávníček, Zdeněk ; Vít, T.
Equipments working on the synthetic jet (SJ) principle can be used in aerospace industry, automotive industry, pumps and ejectors, cooling and heating applications, intensification of mixing in chemical reactors. SJ can be used for jet control and vectoring, flow control in external and internal aerodynamics, intensification of heat transfer. The main advantage of these applications is relative simplicity of SJ equipment. This article summarizes primary SJ world studies, and it shows examples of own experimental results.
|
|
|
Formation criterion for various synthetic jets: power and frequency characteristics
Kordík, Jozef ; Trávníček, Zdeněk ; Šafařík, P.
Synthetic jets are generated by periodic alternating flows. The jet parameters are: dimension, frequency, oscillation shape and amplitude. The Reynolds number (ReH) and Strouhal number (StH) (or Stokes number SH) are used as dimensionless paramers. The experiment was performed for the Reynolds number range of ReH = 500–10000 and Strouhal number range of StH = 0.2–8.9. Flow visualization and hot-wire measurement were performed. The present results focusing on the jet formation criterion agree quite well with the available literature (the criterion ReH crit = 0.16 SH2).
|
guest ::
