Application of Les, Pans and Rans to a Case of Intake Channel Steady Flow Test Bench

Shrnutí Članek se zabyva vyhodnocenim průtokovych vlastnosti (průtokovy součinitel, součinitel přične a tečne rotace) saciho kanalu užitim jak 3-D CFD simulace, tak měřeni. Byla provedena citlivostni studie různych parametrů simulace. Nejdůležitějši jsou vlastnosti sitě a použite modely turbulence (uvažovane modely: LES, PANS a RANS). Co se tyka sitě, tak kritickym parametrem je konfigurace v těsne blizkosti stěny - tloušťka a počet vrstev těsně u stěny maji velky vliv na průtok, avšak součinitele přične a tečne rotace na tom teměř nezavisi. Odtud plyne, že tyto parametry sitě lze považovat za ladici parametry CFD modelu. Co se tyka velikosti oka sitě, 2 velikosti byly testovany (0.6 a 0.3 mm). Ukazalo se, že ani jedna z těchto siti neni dostatečně jemna pro korektni aplikaci LES. A tedy PANS funguje spiše jako RANS. Z hlediska modelů turbulence je PANS jevi jako nejlepši možnost, protože kombinuje vyhody jak LES, tak RANS. Obecně je možne konstatovat, že lze dosahnout relativně dobre shody na průtoku, ale součinitele přične a tečne rotace jsou problematicke, neboť byla dosažena pouze kvalitativni shoda.

Study of the influence of nozzle seat type on injection rate and spray behaviour

A deep analysis of the injection rate characteristics and spray behaviour of the most used nozzle types in diesel engines [microSAC and valve covered orifice (VCO)] has been carried out. In order to compare the injection characteristics and the spray behaviour of both nozzle types, several experimental installations were used, such as the steady flow test rig, injection rate test rig, spray momentum test rig, and nitrogen test rig, to obtain a full hydrodynamic and spray characterization. The study of the flow in both nozzles was analysed under steady flow conditions in the steady flow test rig and in real unsteady flow conditions in the injection rate test rig and the spray momentum test rig. The macroscopic properties of the spray (tip penetration and spray cone angle) were characterized using a high-pressure test rig. From the point of view of the internal flow behaviour, the results showed interesting differences in the permeability of both nozzle geometries, with a higher discharge coefficient in the microSAC nozzle. However, from the point of view of air entrainment, the results showed a better quality of fuel-air mixing in the VCO nozzle. Besides the evidence from the experimental results, a theoretical analysis was carried out in order to identify the most important parameters that determine the spray behaviour and thus justify the different macroscopic behaviour of both nozzles.