Numerical analysis of fluid flow inside air intake system

Transcription

1 Numerical analysis of fluid flow inside air intake system Numerical analysis of fluid flow inside air intake system Regis Ataides Martin Kessler Marcelo Kruger Geraldo Severi Jr. Cesareo de La Rosa Siqueira Walter Zottin Wagner Trindade 1

2 Agenda Introduction Goals Description of the numerical model Geometry and mesh Boundary conditions Numerical model Results Comments Introduction Air intake system is responsible for capturing and cleaning air from vehicle s surroundings, before allowing it to be injected into the engine In addition, information about the mass flow is extracted from the flow and sent to the fuel injection system, which can calibrate the proper mixture to any specific condition. In order to allow for a reliable reading, the flow must be well behaved around the Mass Air Flow Sensor (MAFS) 2

3 Goals Develop a computational model to study the flow inside Air Intake Systems (AIS) Two geometries have been evaluated and the second one with two different honey combs Evaluate the pressure drop for the entire system and identify local pressure losses. In addition, identify the flow pattern around the MAFS Numerical model - Geometry Model 1 Model 2 MAFS 3

4 Numerical model Model 2 with Honeycomb Model 2 HC1 The honeycomb is placed right before the MAFS to reduce the turbulence level Model 2 - HC2 Boundary conditions (Same for all models) Outlet: Pressure Inlet: Mass flow Filtrating element: Inertial resistance Viscous resistance 4

5 Computational Mesh Extension to avoid backflow at the outlet Mesh with around 2,6 million cells for both Model 1 and 2 Computational Mesh Extension Mesh with Honeycomb 1 with 3.1 millions of elements Mesh with Honeycomb 2 with 4.6 millions of elements 5

6 Numerical model Assumptions: Steady-state flow; Isothermal; Incompressible; Turbulent. Fluid properties: Air Density: 1,225 kg/m³; Viscosity: 1,7894e-05 kg/m/s; Results Pressure on the walls Model 1 Model 2 Model 2 HC1 Model 2 - HC2 6

7 Results Pressure drop along the model Average pressure taken at the following surfaces: DirtyAirDuct Elem-Top POut In Elem-Bot CleanAirDuct Results Pressure drop Pressure Mod 1 Mod 2 Mod 2 HC1 Mod 2 HC2 In DirtyAirDuct Elem_top Elem_bot CleanAirDuct After Honey Comb Pout 7

8 Results - Uniformity In order to identify how well behaved is the flow at the outlet, the following uniformity indexes will be applied there: - Eccentricity; - Gamma; - Velocity ratio; Results Uniformity Coefficients - Definitions Eccentricity (ε): Evaluate how distant from the center the maximum velocity point is: 0: At the center (best) 1: In the border (worst) ε = ε x ε y For an ellipsis: ε x = 2 ( x x ) v max L major mid ε y = ( y y ) 2 v max L min or mid 8

9 Results Uniformity Coefficients - Definitions Gamma (γ): Evaluate how uniform is the velocity distribution on a given surface. Gamma = 1: Uniform (best) Gamma = 0: Non-uniform (worst) γ = i 1 ( v v A ) 2v avg A avg total i Results Uniformity Coefficients - Definitions Velocity ratio (v ratio ): Is the ratio between the maximum and the average velocity on a surface. Around 1 is better. v ratio = v v max mean 9

10 Results Uniformity Coefficients LDV Uniformity coefficients LJ1 Ecc Gamma Velocity ratio Model Model Model 2 HC LKF 1.19 Model 2 HC Results Velocity vector at the MAFS region Model 1 Model 2 Model 2 HC1 Model 2 HC2 10

11 Results Turbulence intensity around the Honey Comb Cut plane before the Honey Comb Model 2 HC1 Model 2 HC2 Cut plane after the Honey Comb Results Turbulence intensity around MAFS region Model 2 Model 2 HC1 Model 2 HC2 The Honey comb reduces the turbulence intensity around MAFS region 11

12 Results Pathlines Model 1 Model 2 Model 2 HC1 Model 2 HC2 Comments Both honeycomb designs reduced the turbulence intensity at the MAFS region when compared to the model without it; The pressure drop, on the other hand, increased slightly with the honeycomb; The pressure drop curve was affected only at the honeycomb region, keeping the same behavior in the rest of the domain; The eccentricity at a cut plane upstream the MAFS changed from 0.31 in the first configuration with honeycomb (Model 2 HC1) to 0.53 in the second (Model 2 HC2). 12