Haider, Sajjad

Ingvorsen, Kristian Mark

Meyer, Knud Erik

Obeidat, Anas

Walther, Jens Honore

We study the effect of piston motion on the in-cylinder swirling flow in a low speed, large two-stroke marine diesel engine. The work involves experimental, and numerical simulation using OpenFOAM platform, Large Eddy Simulation was used with three different models, One equation Eddy, Dynamic One equation Eddy, and Ta Phouc Loc model, to study the transient phenomena of the flow. The results are conducted at six cross sectional planes along the axis of the cylinder and with the piston displaced at four fixed piston positions covering the air intake ports by 0%,25%, 50%, and 75% respectively, for the fully opened case LES model with 8/12 million mesh points were used. We find that the flow inside the cylinder changes as the ports are closing, from a Rankine/Burger vortex profile to a solid body rotation while the axial velocity profiles change from a wake-like to a jet-like profile

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Dec 20, 2017Influence of piston displacement on the scavenging and swirling flow in two-strokediesel enginesObeidat, Anas Hassan MohD; Haider, Sajjad; Ingvorsen, Kristian Mark; Meyer, Knud Erik; Walther, JensHonorePublication date:2012Link back to DTU OrbitCitation (APA):Obeidat, A., Haider, S., Ingvorsen, K. M., Meyer, K. E., & Walther, J. H. (2012). Influence of piston displacementon the scavenging and swirling flow in two-stroke diesel engines. Abstract from 23rd Nordic Seminar onComputational Mechanics, Stockholm, Sweden.23rd Nordic Seminar on Computational MechanicsNSCM-23A. Eriksson and G. Tibert (Eds)c©KTH, Stockholm, 2010INFLUENCE OF PISTON DISPLACEMENT ON THE SCAVENGINGAND SWIRLING FLOW IN TWO-STROKE DIESEL ENGINESA. OBEIDAT†, S. HAIDER,† K. M. INGVORSEN †, K. E. MEYER†, ANDJ. H. WALTHER ††Department of Mechanical EngineeringTechnical University of DenmarkDK-2800 Kgs. Lyngby, DenmarkTel.: +45-4525 4327Fax: +45-4588 4325Key words: diesel engine, swirl, scavenging, LES simulation.Summary. We study the effect of piston motion on the in-cylinder swirling flow in a low speed,large two-stroke marine diesel engine. The work involves experimental, and numerical simulation usingOpenFOAM platform, Large Eddy Simulation was used with three different models, One equation Eddy,Dynamic One equation Eddy, and Ta Phouc Loc model, to study the transient phenomena of the flow.The results are conducted at six cross sectional planes along the axis of the cylinder and with the pistondisplaced at four fixed piston positions covering the air intake ports by 0%,25%, 50%, and 75% respec-tively, for the fully opened case LES model with 8/12 million mesh points were used. We find that theflow inside the cylinder changes as the ports are closing, from a Rankine/Burger vortex profile to a solidbody rotation while the axial velocity profiles change from a wake-like to a jet-like profile.1 INTRODUCTIONIn two stroke engines, compared to 4-stroke engines, the removal of exhaust gases and supply of freshair for the next cycle is carried out simultaneously using the scavenging process. Scavenging is carriedout using air entering the cylinder from intake ports at the cylinder liner walls near the bottom deadcentre and scavenging the exhaust gases from cylinder through the exhaust port. The scavenging processremoves the exhaust gases, provides fresh air to the engine , and provides the necessary swirl to the flowin which the diesel fuel is to be injected. This makes the scavenging process very important for engineperformance and efficiency both in terms of fuel consumption and emissions. Swirling flows are widelyused in industrial applications e.g. cyclone separators, swirl combustors etc. Previous studies1 2 3 involveswirl generators using guide vanes that divert the radially incoming flow and impart the tangential com-ponent. In the present study we focus on the swirling flow in the presence of an obstructing piston andthe resulting in-cylinder confined swirling flow.1A. Obeidat, S. Haider, K. M. Ingvorsen, K. E. Meyer and J. H. Walther2 NUMERICAL METHODS2.1 LARGE EDDY SIMULATIONWe study the swirling flow numerically using large eddy simulations. The governing equation are thespatially filtered Navier-Stokes equations:∂ u¯ j∂x j= 0 (1)∂ u¯i∂ t+∂ u¯iu¯ j∂x j=− 1ρ∂ p¯∂xi+ν∂ 2u¯i∂x2j− ∂τSGSi j∂x j(2)τi j = ρ¯ u˜iu j− ρ¯ u˜iu˜ j (3)where t denotes the time, ui is the velocity component in Cartesian coordinates, ρ is the density, p is thepressure, and ν is the kinematic viscosity. As a result of the spatial filtering the subgrid-scale-stresses(SGS) stress tensor τSGSi j is introduced into the momentum eq. (2), where τSGSi ji j = uiu j− u¯iu¯ j.5 6 7 8 9 10 11We apply three different models. The one equation eddy model where the kinetic energy k is solvedwhile another scale is estimated, so if the k is solved then the turbulent velocity u is estimated by u∗ ∼√k 5. Eddy viscosity µi =Cµ ρ¯k12 l∗, where Cµ is a constant, l∗ is the turbulent length scale.The dynamic k-equation eddy-viscosity model, where the model constants are recalculated during thesimulation rather than to be pre-calculated, the model stress tensor eq. (3)12 which can be modeled asτi j− 13δi jτkk =Cαi j C =Li jMi jMklMkl(4)where C is the model parameter, Mi j is the minimum error, Li j is a stress resolved tensor. αi j is the termneeded to be modeled.5 12αi j =−2ρ¯∆2(2S˜kl S˜kl) 12 S˜i j (5)where S˜i j is the filtered strain tensor.The Ta Phouc Loc model, which is based on the velocity-vorticity (v-ω) formulation of the Navier-Stokes equations. Two spatial filters are used, the first filter denoted by (−) is used on the fine mesh, andthe second ’test filter’ denoted by (∼) which is used on the coarse mesh. From eq. (2) we find thatτi j = U¯iU¯ j =UiU j = (U¯iU¯ j−U¯iU¯ j)− (U¯iU j ′+Ui′U¯ j)−Ui′U j ′ (6)where the fluctuations are defined as Ui′ =Ui−U¯i.The turbulent stresses are modeled asτi j = vt(∂U¯i∂x j+∂U¯ j∂xi)− 23kδi j (7)The eddy viscosity vt is determined by the mixed-scale turbulence model introduced by L.Ta Phouc13vt =C |ω¯|α k(1−α)/2∆(1+α) (8)where ω is the vorticity, ∆ = (∆x∆y∆z)13 is an average grid size, k is the turbulent kinetic energy, α is aparameter which takes a value between 0 and 1. From a previous study14 it was found that the modelperforms best when α = 0.5.2A. Obeidat, S. Haider, K. M. Ingvorsen, K. E. Meyer and J. H. WaltherThe turbulent kinetic energy is estimated from the test filter (∼) ask =123∑j=1(U j−U¯ j)2 ≈ 123∑j=1(U¯ j− ˜¯U j)2(9)where U j is the unfiltered velocity field and ˜¯U j is the doubled filtered velocity field obtained by applyingthe second filter on the resolved velocity U¯ j.13 14 152.2 COMPUTATIONAL DOMAIN AND RESULTSThe computational domain is shown in Fig. 1 and consists of an inlet section (swirl generator), acylinder and an outlet section. At the inlet of the computational domain a uniform radial and tangentialvelocity is defined and at the outlet a zero-gradient boundary condition is applied.(a)Figure 1: 3D cross sectional view showing the velocity magnitude, vorticity contours (in white) and streamlines.The results shown in Fig. 2 show that generally there is a good agreement between computationaland experimental particle image velocimetry (PIV) results that have been measured previously4. Themodels capture the wake and jet like profiles of the axial velocity but both are not as pronounced as inthe experimental results.3A. Obeidat, S. Haider, K. M. Ingvorsen, K. E. Meyer and J. H. Walther−1.0 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 1.00.40.60.81.01.21.41.61.8   0.40.6Xv/RV z/ Vb  DynamicLocOneEqEddyExp.(a)−1.0 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 1.0−0.8−0.6−0.4−0.20.0 0.2 0.4 Xv/RV Θ/ Vb  DynamicLocOneEqEddyExp.(b)−1.0 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 1.00.40.60.81.01.21.41.61.8Xv/RV z/ Vb  OneEqEddyExp.(c)−1.0 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.8 1.0−0.4−0.3−0.2−0.10.0 0.1 0.2 0.3 0.4 Xv/RV Θ/ Vb  OneEqEddyExp.(d)Figure 2: (a) (c) Time averaged axial velocity profiles for the 100%,50% open ports, (b) (d) Time averaged tan-gential velocity profiles for the 100%,50% open ports, at the axial position z/D = 2.016REFERENCES[1] Kitoh, S. Experimental Study of turbulent swirling flow in a straight pipe. J. Fluid Mech. 225,445–479 (1991).[2] Algifri, A. H., Bhadwaj, R. K. & Rao, Y. V. N. Turbulence Measurements in Decaying Swirl Flowin a Pipe. Applied Scientific Research 45, 233–250 (1988).[3] Escudier, M. P., Bornstein, J. & Maxworthy, T. The dynamics of confined vortices. Mathematicaland Physical Sciences 382, 335–360 (1982).[4] Haider, S. Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-StrokeMarine Diesel Engines. Ph.D. thesis, Technical University of Denmark (2010).[5] Wang, P. Large Eddy simulation of Turbulent Swirling Flows and Turbulent Premixed Combustion.Ph.D. thesis, Lund Institute of Technology (2005).[6] Dejoan, A., Jang, Y. J. & Leschziner, M. A. Comparative LES and Unsteady RANS Computationfor a Periodically-Perturbed Separated Flow over a Backward-Facing Step. Fluids Eng. 127, 872–879x (2005).4A. Obeidat, S. Haider, K. M. Ingvorsen, K. E. Meyer and J. H. Walther[7] Narasimhamurthy, V. Unsteady RANS simulation of Turbulent Trailing-Edge Flow. Ph.D. thesis,Chalmers University of Technology (2004).[8] Wegner, B., Schneider, C., Dreizler & Janicka, J. Assessment of unsteady RANS in predicting swirlflow instability based on LES and experiments. Int. J. Heat Fluid Flow 25, 528–536 (2004).[9] Wang, P. & Bai, X. S. Large eddy simulation and experimental studies of a confined turbulentswirling flow. Phys. Fluids (2004).[10] Lesieur, M., Metais, O. & Comte, P. Large Eddy Simulations of Turbulence (Cambridge UniversityPress, 2005).[11] Moene, A. F. Swirling pipe flow with axial strain Experiment and Large Eddy Simulation. Ph.D.thesis, Technische Universiteit Eindhoven (2003).[12] Germano, M., Piomelli, U., Moin, P. & Cabot, W. H. A dynamic subgrid-scale eddy viscositymodel. Phys. Fluids 3, 1760–1765 (1991).[13] Tenaud, C., Pellerin, S., Dulieu, A. & Phouc, L. T. Large Eddy simulations of spatially developingincompressible 3D mixing layer using the v−ω formulation. Computers & Fluids 34, 67–96(2005).[14] Shen, W. Z., Zhu, W. & Sorensen, J. N. Aeroacoustic computations for turbulent airfoil flows.AIAA 47 (2009).[15] Sagaut, P. Large Eddy Simulation for Incompressible Flows (Springer), 3 edn.5

Influence of piston displacement on the scavenging and swirling flow in two-stroke diesel engines

http://orbit.dtu.dk/ws/files/12697760/Obeidat:2010.pdf

Influence of piston displacement on the scavenging and swirling flow in two-stroke diesel engines

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology