Dr Amirhasan Kakaee, Mr Mohammadreza Karami,
Volume 9, Issue 2 (6-2019)
Abstract
In this study, modeling of a fuel jet which has been injected by high pressure into a low-pressure tank are investigated. Due to the initial conditions and the geometry of this case and similar cases (like CNG injectors in internal combustion engines (ICE)), the barrel shocks and Mach disk are observed. Hence a turbulence and transient flow will be expected with lots of shocks and waves. According to the increasing usage of this type of injectors in ICE, more studies should be conducted to find the most accurate and beneficial models for modeling this phenomenon.
In order to find an accurate and beneficial turbulence model ,in this study, three Reynolds-averaged Navier–Stokes (RANS) turbulence models (SST k-ω, RNG and standard k ) and large eddy simulation (LES) turbulence model were compared by the fuel jet characteristics in three regions (outlet of the nozzle, at Mach disk and at the downstream of the flow). Although the LES model needs more time for each test, the results are more reliable and accurate. On the other hand, RANS turbulence models have lots of errors (more than 10 percent) especially for predicting the characteristics of fuel jet at Mach disk.
Mr Amirhasan Kakaee, Mr Milad Mahjoorghani,
Volume 10, Issue 2 (6-2020)
Abstract
Intake and exhaust manifolds are among the most important parts in engine in which pressure loss phenomena has direct impact on with changing volumetric efficiency. In typical 1D simulation codes, the quantity of pressure loss is proportional to the fluid’s mean velocity by Pressure Loss Coefficient (Kp) value. This important coefficient which has substantial rule in engine simulation is usually determined using constant available values, extracted from complicated experiments (like Miller’s tests) in a specified situation. But these values are credible only in situations according to those tests. Coupling 3D simulations with 1D codes is a common method to gain accurate values of these coefficients but this deals with drastic high simulation costs. To address this problem, a more efficient way is replacing an algebraic relation, extracted from 3D calculations, instead of a constant value in 1D code. It’s obvious that in order to reach accurate coefficients in arbitrary conditions (geometric and flow specifications) determining the best numerical method is mandatory. In present research, after investigating all 3D simulation aspects, six different selected numerical solutions have been implemented on four different bends in ANSYS Fluent.Results have been validated by comparing loss coefficient values of incompressible fluid (water) with Miller loss coefficient values and method with the most accurate and stable results has been discovered. It was found that all these methods are suitable in general (with less than 5% error in coefficient values) but solutions with structured grid and SST k-ω turbulence modeling represented better stability and accuracy.
