IJISET - International Journal of Innovative Science, Engineering & Technology, Vol. 1 Issue 7, September 2014.

www.ijiset.com

ISSN 2348 – 7968

CFD Analysis for Flow through Glass Wool as Porous Domain in Exhaust Muffler

S.RajaduraiP

1P, Suraj SukumaranP

2P, P.MadhusudhananP

2

P

1PHead R&D, Sharda Motor Chennai, Tamilnadu, India

P

2PSr. Engg R&D, Sharda Motor Chennai, Tamilnadu, India

AbstractThe paper summarizes a candid methodology of simulating a precise pressure drop analysis using computational fluid dynamics (CFD) for an exhaust muffler assembly having glass wool. The traditional CFD methodology does not consider glass wool because the pressure drop simulation with glass wool gives a deviation of 20-40% with experimental data due to inconsistent structure. A novel modeling approach is presented which includes the glass wool region as POROUS DOMAIN in exhaust muffler. Coefficient of porosity in glass wool is calculated from one dimensional gas simulation software - WAVE by Ricardo. Analysis is simulated using CFD code via Star CCM+ by CD-Adapco. The simulated pressure drop results using CFD with glass wool are compared with those of the experimental data which are in very good agreement. Keywords: co-efficient of porosity, exhaust muffler, glass wool, porous domain, precise, pressure drop, 1D analysis.

1. Introduction Stern demand for exhaust system development from OEM’s, necessitates tier-1 suppliers to develop systems in a stringent time frame. Simulation comes into play to cover up these design and development (D&D) time and consecutively to reduce prototype cost. Even though precise analytical prediction helps in reducing D&D time frame, analyst always has to follow the experimental results. Finite volume methods are used to obtain flow characteristics and backpressure values of mufflers. Absorptive mufflers are difficult to analyze using CFD because of its inconsistency and complexity in modeling glass wool (porous media). CFD and experimental results deviates while validating pressure drop across the glass wool muffler system. Coefficients of porosity are calculated from experimental data but preparing an exhaust muffler proto initially and then analyzing using CFD does not give an optimum and cost effective solution.

Therefore, it requires a highly fidelity 1D tool like WAVE which can calculate pressure drop values of an exhaust muffler including glass wool properties. Hence, co-efficient of porosity can also be calculated from 1D pressure drop. Having used of this method, effect of backpressure on different parameters can be examined without prototyping and best suitable muffler can be determined in the design phase itself. Further value targeted product can be achieved in time and low cost. Design and analysis of flow characteristics of exhaust system by Atul A. Patil studies the effect of backpressure on engine performance [1]. Change in porosity of internal tube has pronounced effect on the backpressure. If the porous area increases the back pressure will increase respectively [2]. Muffler pre-processing methodology and comparative study by Rajadurai et al. points out pre-processing methodology of CFD tool having glass wool inserted into an exhaust chamber should split as a separate collector region for assigning glass wool properties [3]. Studies on mathematical modeling of porous media to find inertial resistance and viscous resistances, explains pressure drop test on a porous media should initially conduct and subsequently the corresponding analysis are simulated using CFD for precise pressure drop analysis across porous media [4]. Conventionally CFD analysis is performed for reactive mufflers [5-8]. CFD analysis on absorptive mufflers using glass wool is very uncommon. A novel approach is undertaken to model a glass wool region in CFD and also effective method to calculate porous coefficients for glass wool. By this method a precise and specific flow characteristics could attain for absorptive type of exhaust mufflers.

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IJISET - International Journal of Innovative Science, Engineering & Technology, Vol. 1 Issue 7, September 2014.

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ISSN 2348 – 7968

2. Simulation Model CAD model of the present muffler which will be examined in the paper is shown in fig.1. As shown, in fig.1 the muffler consists of perforated inlet and outlet pipes and one perforated tube and two non-perforated baffles. The perforated rates of inlet pipe, outlet pipe and tube are approximately 31%, 34% & 34% respectively. Furthermore the muffler has three expansion chambers. Glass wool is packed in perforated parts i.e. in middle chamber. Perforated parts of inlet and outlet pipes create a cross flow inside the muffler.

Fig. 1 CAD model of base muffler

3. Three Dimensional Study A three-dimensional model of exhaust muffler with glass wool is generated in CFD tool Star CCM+ v9.02 for the analysis. 3.1 Modeling and Meshing The geometry of the element is made as polyhedral mesh, with a refined prism layer mesh near the wall. The k-ε turbulence model is used, with standard wall functions for near-wall treatment. The model has approximately 1.4 million cells with maximum skewness angle of 85 degree. 3.2 Governing Equations CFD solver Star CCM+ is used for this analyze. It is a finite volume approach based solver which is widely used in industries. Governing equations solved by the software for these analyze in tensor Cartesian form are following: Continuity:

𝜌 �𝜕𝑢𝑗𝜕𝑥𝑗

� = 0

Momentum:

𝜌𝜕𝜕𝑥𝑗

(𝑢𝑗𝑢𝑖) = −𝜕𝑝𝜕𝑥𝑗

+𝜕𝜏𝑖𝑗𝜕𝑥𝑗

+ 𝑆𝑐𝑜𝑟 + 𝑆𝑐𝑓𝑔

Where ρ is density, 𝑢𝑗R Ris jth Cartesian velocity, p is static pressure, 𝜏𝑖𝑗R Ris viscous stress tensor.

4. Boundary Conditions Air is used as fluid media, which is assumed to be steady and comparable. High Reynolds number k-ε turbulence model is used in the CFD model. This turbulence model is widely used in industrial applications. The equations of mass and momentum are solved using SIMPLE algorithm to get velocity and pressure in the fluid domain. The assumption of an isotropic turbulence field used in this turbulence model is valid for the current application. The CFD analysis of this model would be passing air at fixed mass flow rate through the muffler and measuring pressure drop across the glass wool muffler system under ambient temperature. The time conditions implemented are steady state. The mass flow input is 50 kg/h to 200 kg/h at 303K and outlet pressure of 1 atm. 5. Post Processing Results - Traditional Methodology (Without Glass Wool) The velocity, pressure and temperature contour for the muffler test in CFD without considering glass wool is shown in fig 2.

(a) Velocity (m/s) contour plot

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IJISET - International Journal of Innovative Science, Engineering & Technology, Vol. 1 Issue 7, September 2014.

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ISSN 2348 – 7968

(b) Pressure (kPa) contour plot

(c) Temperature (K) contour plot

Fig. 2 Post processing results - Without considering glass wool

6. Experimental Setup

Fig. 3 Experimental setup for back pressure

The experimental setup of cold flow air control system for backpressure measurement is shown in fig 3. Backpressure across the system is analyzed with the aid of differential pressure sensor by placing the front & rear measuring ends at 50mm distance form inlet & outlet of muffler assembly respectively. Mass flow rate is increased from 50 to 200 kg/h & the measurements are acquired for two minutes time span at all stages. CFD analysis of the muffler tested in experiment has been performed. All the solver conditions, turbulence modeling

and boundary conditions except glass wool have been kept same as in the experimental analysis of muffler system. The actual test setup is shown in fig 4. The CFD results without considering glass wool are shown in table I and comparison chart is shown in fig. 5. CFD and experimental values shows 21% to 44% of deviation which evidently shows flaws in traditional methodology.

Fig. 4 Muffler tested in lab

Table I: Test Lab Vs CFD (without glass wool) results

Fig.5 Pressure drop comparison of experimental and CFD (without glass

wool) value

MFR (kg/h) 𝚫𝐩 (kPa) Test Lab

𝚫𝐩 (kPa) CFD

% Error

50 0.16 0.089 -44 100 0.46 0.34 -26 150 1 0.77 -23 200 1.74 1.36 -21

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IJISET - International Journal of Innovative Science, Engineering & Technology, Vol. 1 Issue 7, September 2014.

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ISSN 2348 – 7968

7. Problem Definition The problem is to correlate CFD boundary conditions with real time simulations which necessitate reducing design and development time. Porous coefficients of glass wool can also be calculated from experimental data. But to reduce prototype cost and design process, it can also be calculated from 1D simulation (e.g. WAVE). 8. Glass Wool Modeling - Novel Approach Glass wool is packed in perforated parts. In CFD a 3D geometry glass wool part cannot be merged and meshed with perforated geometry pipes. Therefore the novel approach to model glass wool region is to close all the upper layer of the perforated holes as shown in fig 6.

Fig. 6 Closing the upper layer of perforated holes

After closing all the upper layer of perforated holes and non-manifold edges the muffler surface topology will be split up in to two domains i.e. fluid domain and porous domain (middle chamber) as shown in fig 7.

(a) Fluid Domain

(b) Porous Domain

Fig. 7 Muffler Surface Topology

9. Mathematical Modeling - Porous Glass Wool For porous media, it is assumed that, within the volume containing the distributed resistance there exists a local balance everywhere between pressure and resistance forces such that [4].

−𝐾𝑖𝑣𝑖 =𝜕𝑝𝜕𝜉𝑖

Where 𝜉𝑖 (i = 1, 2, 3) represents the (mutually orthogonal) orthotropic directions. 𝐾𝑖 is the permeability, 𝑣𝑖 is the superficial velocity in direction 𝜉𝑖 The permeability 𝐾𝑖 is assumed to be a quasi linear function of the superficial velocity. Superficial velocity at any cross section through the porous medium is defined as the volume flow rate divided by the total cross sectional area (i.e. area occupied by both fluid and solid). To find the inertial resistance and viscous resistance the pressure drop analysis was conducted in 1D WAVE simulation for mass flow rates from 50 kg/h to 200 kg/h. The mass flow values are converted to velocities using the flow area and air density and corresponding pressure drop results are shown in table 2. Velocity (U) v/s Pressure drop (Δp) plotted in the graphical representation. From the plot we can find the polynomial function for the pressure drop shown in fig. 8.

Table 2: 1D Data from WAVE

Velocity (m/s) ΔP (kPa) WAVE 0 0

0.5 0.11 1 0.5

1.5 1.08 2 1.79

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IJISET - International Journal of Innovative Science, Engineering & Technology, Vol. 1 Issue 7, September 2014.

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ISSN 2348 – 7968

Fig.8 Regression curve showing Velocity Vs Pressure Drop Plot

For porous media,

Δp𝐿

= −(𝑃𝑖𝗅v𝗅 + Pv)v Where, L is the length of the porous media in stream wise direction. 𝑃𝑖 = 𝑎

𝐿 is porous inertial resistance. 𝑃𝑣 = 𝑏

𝐿 is

porous viscous resistance. v is the superficial velocity The polynomial equation for unit length,

Δp = 2035.484𝑥2 + 444.1935𝑥 Calculated Porosity Coefficients from 1D analysis, Porous Inertial Resistance (Pi) = 2035.484 kg/m^4 Porous Viscous Resistance (Pv) = 444.193 kg/m^3-s 10. Observations The velocity, pressure and temperature contours for the muffler test in CFD considering porous glass wool along cross- stream directions is shown in fig 9. From post processing results it can be observed that with glass wool temperature flow is less and pressure drop value is high across the glass wool muffler system. With glass wool velocity decrease and pressure drop increase, hence more sound will attenuate for absorptive type of exhaust mufflers.

(a) Velocity (m/s) contour plot

(b) Pressure (kPa) contour plot

(c) Temperature (K) contour plot

Fig.9 Post processing results - With considering glass wool

The CFD results considering glass wool are shown in table 3 and comparison chart is shown in fig.10. Both CFD and experimental values have less than 2% deviation which clearly indicates that the novel approach followed correlates with the real time condition of glass wool muffler system. Unlike 1D WAVE simulation, in CFD gas distribution can be well studied across glass wool muffler system which will be constructive to optimization for internal exhaust parts.

Table 3: Test Lab Vs CFD (with glass wool)

MFR (kg/h) 𝚫𝐩 (kPa) Test Lab

𝚫𝐩 (kPa) CFD

% Error

50 0.16 0.118 -26

100 0.46 0.453 -1.5

150 1 1.008 0.8

200 1.74 1.764 1.3

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Fig.10 Pressure drop comparison of experimental and CFD (with glass

wool) values 11. Conclusion Fully utilizing the 1D WAVE simulation, porous calculation for glass wool can be done. These data proved to be useful in calculating a precise backpressure distribution and flow characteristics for an exhaust muffler assembly. Thus helping in validating the muffler system for various experimental test like thermal shock, acoustics, etc.

References

[1] Atul A. Patil, L.G. Navale and V.S. Patil, "Design, Analysis of Flow Characteristics of Exhaust System and Effect of Back Pressure on Engine Performance", IJEBEA, 2014.

[2] Sudarshan Dilip Pangavhane, Amol Bhimrao Ubale, Vikram A Tandon and Dilip R Pangavhane, "Experimental and CFD Analysis of a Perforated Inner Pipe Muffler for the Prediction of Backpressure, IJET, Oct-Nov 2013.

[3] S. Rajadurai, Suresh Natarajan and N. Manikandan, "Muffler

Pre-Processing Methodology and Comparative Study Using Hypermesh", HTC conference, 2012.

[4] P.Karuppusamy and R. Senthil, “Design, analysis of flow characteristics of catalytic converter and effects of backpressure on engine performance", IJREAT, Issue 1, Volume 1, March-2013.

[5] D. Tutunea, M.X. Calbureanu and M. Lungu, "The computational fluid dynamics (CFD) study of fluid dynamics performances of a resistance muffler", IJOM, Issue 4, Volume 7, 2013.

[6] Dragos Tutunea, Madalina and lungu Mihai, "Computational

fluid dynamics analysis of a resistance muffler", Recent Advances in Fluid Mechanics and Heat & Mass Transfer, 1978.

[7] Yunshi Yao, Shaodong Wei, Jinpeng Zhao, Shibin Chen,

Zhongxu Feng and Jinxi Yue, "Experiment and CFD Analysis of Reactive Muffler", RJASET, March-2013.

[8] Zeynep Parlar, Sengul Ari, Rıfat Yilmaz, Erdem Ozdemir, and

Arda Kahraman, "Acoustics and flow field analysis of a perforated muffler design", WASET, Volume 7, 2013.

[9] Erdem Ozdemir, Rifat Yılmaz, Zeynep Parlar and Sengul Arı,

"An analysis of geometric parameters effects on flow characteristic of a reactive muffler", Istanbul Technical University, 17th International Research Expert Conference, sept-2013.

[10] Star CCM+ User Guide.

Acknowledgement The authors would like to thank Mr. S. Ananth, Sharda Motor, R&D for designing the CAD geometry and also Mr. Aditya Prabakar, Technical Support Engineer from CD-Adapco for his help in Star CCM+ software. Biographies Dr. S. Rajadurai, Ph. D.

Dr. S Rajadurai, born in Mylaudy, Kanyakumari District, Tamil Nadu, India, received his Ph.D. in Chemistry from IIT Chennai in 1979. He has devoted nearly 35 years to scientific innovation, pioneering theory and application through the 20P

thP century, and

expanding strides of advancement into the 21P

stP

century. By authoring hundreds of published papers and reports and creating several patents, his research on solid oxide solutions, free radicals, catalyst structure sensitivity, and catalytic converter and exhaust system design has revolutionized the field of chemistry and automobile industry.

Dr. Rajadurai had various leadership position such has the Director of Research at Cummins Engine Company, Director of Advanced Development at Tenneco Automotive, Director of Emissions at ArvinMeritor, Vice-President of ACS Industries and since 2009 he is the Head of R&D Sharda Motor Industries Ltd. He was a panelist of the Scientists and Technologists of Indian Origin, New Delhi 2004. He is a Fellow of the Society of Automotive Engineers. He was the UNESCO representative of India on low-cost analytical studies (1983-85). He is a Life Member of the North American Catalysis Society, North American Photo Chemical Society, Catalysis Society of India, Instrumental Society of India, Bangladesh Chemical Society and Indian Chemical Society.

Suraj Sukumaran

Suraj Sukumaran is a Sr. Engineer at Sharda Motor, R&D, Chennai. During his academic year, he was awarded in merit list for achieving 44th rank among 2407 students in Mechanical Engineering department from Anna University, Chennai. He has been involved in simulating Flow Thermal analysis in CFD for automobile exhaust system of

passenger cars and off road vehicles. His area is mainly on flow & heat transfer simulation including uniformity index, velocity index, pressure drop, HEGO index, conjugate heat transfer analysis and chemical modeling. He is currently working on methodologies and strategies in CFD analysis for better optimization of exhaust system development. He is also involved in various advanced development research like SCR, DPF, COR2R & NHR3R.

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IJISET - International Journal of Innovative Science, Engineering & Technology, Vol. 1 Issue 7, September 2014.

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ISSN 2348 – 7968

P. Madhusudhanan P. Madhusudhanan is a Sr. Engineer at Sharda Motor, R&D, Chennai. He is a multi role performer in the path of excellence in flow sciences. His job profile as flow lab in charge come CFD analyst paved the ways to understanding the virtual & real condition flow behavior and also his pursuing master degree in engineering is assisting him to broaden his view point from theory to application.

The current researches over know-how of flow behavior in emission & sound control devices has led to the development of 1-d tools which is evaluated with virtual & real condition analysis. .

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