Ricardo Tutorial

Figure 2: Exhaust manifold schematic

Using the Elements Tree, place all of the required junctions and then draw the required ducts as shown in Figure 3. Connect the dangling ducts from the exhaust ports to the newly created orifice junctions. Remember to create a hanging duct leaving the collector Y-junction to represent the connection with the close-coupled catalytic converter.

Figure 3: Exhaust manifold flow elements in WaveBuild

Define all the ducts using the values shown in the schematic. Remember to use 40 [mm] for the Discretization Length and set the Initial Conditions to a Pressure of 1.05 [bar], Fluid Temperature of 1100 [K], and Wall Temperature of 750 [K].

1.3 Defining the Collector and Catalyst Connection

The hanging duct that will be connected to the close-coupled catalytic converter can be assigned Left and Right Diameters of 76 [mm] and an Overall Length of 0 [mm] (i.e. it is a massless duct). This will approximately model a direct connection between the collector volume and the entry to the catalytic converter. Define the Y-junction representing the collector using the values shown in the schematic. Once the Diameter of 80 [mm] has been entered, click on the auto-calculate buttons to fill in the Volume and Heat Transfer/Skin Friction Area fields automatically. The Wall Temperature of the collector should be higher than the runners. Assign similar initial conditions as the runners, but use a Wall Temperature of 900 [K]. When completed, the Y-junction Panel for the collector should appear as in Figure 4.

Figure 4: Collector Y-Junction Panel

Orient the ducts as they are displayed in the schematic in Figure 1. Orient the massless duct leaving the collector to be facing down, out of the plane of the runners, as shown in Figure 5.

Figure 5: Collector Duct Orientation

When completed, the model should appear as in Figure 6.

Figure 6: Model with Completed Manifold

Save your model Select the Save As... option from the File pull-down menu and give the model a new name, such as tut_si4_exhaust.wvm . Saving this file and running it with a different name will allow comparison of results to the models built and analyzed earlier.

Proceed to Step 2 - The Catalytic Converter

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SI Tutorial, Phase 5 - Adding the Exhaust System and Creating Spatial Plots in WavePost Step 2 - The Catalytic Converter The catalytic converter consists of entry and exit cones that will be modeled using volumes and a brick, which can be modeled using a catalyst duct. The catalyst duct allows the user to input typical catalyst measures, like cell density, to represent the geometry of the brick.

Chapter sections

Example Input File:

2.1 The Basic Geometry

.\Ricardo\WAVE\8.0\examples\engine\TUT_si\tut_si4_exhaust.wvm

2.2 The Entry and Exit Cones

Example Output File:

2.3 The Brick as a Catalyst Duct

.\Ricardo\WAVE\8.0\examples\engine\TUT_si\tut_si4_exhaust.wps


The schematic of the catalytic converter is shown in Figure 1. In WaveBuild, the entry and exit cones can be modeled using Complex Y-junctions and the catalyst brick can be modeled using a single Catalyst Duct connecting the two junctions. Drag and drop the required elements onto the canvas and connect them. Don't forget to attach the dangling end of the massless duct created with the exhaust manifold to the Y-junction representing the entry cone. See Figure 2.

Figure 1: Catalytic Convert Schematic

Figure 2: Required Junctions and Duct

2.2 The Entry and Exit Cones

The entry and exit cones of the catalytic converter are modeled using complex Y-junctions in order to account for the pressure loss due to sudden expansion of the gas. The taper angle in these cones typically far exceeds the recommended maximum of 7, so using a duct to model the entry/exit cones won't capture the pressure loss due to sudden expansion (see sidebar on Modeling Tapered Ducts). Double-click on the entry and exit cone Y-junctions and edit their settings to reflect the information given in the schematic. The Diameters provided are the area-weighted average diameters, the Volumes and Heat Transfer/Skin Friction Areas are taken from solid-modeling software (CAD). Set the Initial be 1.05 [bar] Pressure, 1100 [K] Temperature, Conditions to and 900 [K] Wall Temperature (see Figure 3).

Figure 3: Entry Cone Y-Junction Panel

Orient the duct connections to be directly across from each other for each Y-junction. The DELX values for both connections should be the length of the cone ( 50 [mm] for both junctions) while the DIAB value can be left as the default value for now, identical to the junction diameter setting: 90.2 [mm] for the entry cone and 76.4 [mm] for the exit cone. Set a Disch. Coeff . of 0.95 for both the entrance and exit connections of the catalyst to account for the tapered cone geometry (see Figure 4).

Figure 4: Catalyst Duct Orientation

2.3 The Brick as a Catalyst Duct

The catalyst brick itself is modeled using a single Catalyst Duct which will actually only represent one channel through the brick but creates a number of identical channels to represent the entire brick. The Catalyst Duct is simply an element which allows input of basic geometric parameters of a the brick in order to describe the single flow channel. Figure 5 shows the method used to calculate the diameter of a single catalyst brick channel and the number of identical channels. It assumes that all channels are square in shape. Given the geometry of the brick, the catalyst duct should be specified to have a Cross Sectional Area of 7854 [mm 2], a Perimeter of 314.59 [mm], a Cell Wall Thickness of 4 [mil], and a Cell Density of 600 [1/in2].

Figure 5: Calculating Catalyst Geometry

The Overall Length should be 80 [mm] as shown in Figure 1 and remember to set the Discretization Length to 40 [mm]. Using the formula shown in Figure 5, the Cell Count should be equal to 7304 and the Cell Diameter (single channel) should be 1.055 [mm], as shown in Figure 6.

Figure 6: Catalyst Brick Geometry

Edit the neighboring Y-junctions representing the entry and exit cones and set the DIAB value for the catalyst duct connection to be 1.17 [mm] (this represents the expansion diameter for a single channel entering the volume). A common practice when modeling Catalytic Converters in steady-state, if test data is available, is to set the brick Wall Temperature to match the temperature of the gas on the downstream side of the catalyst (from the test data) and then set the Heat Transfer Multiplier to a high value, such as 5. This ensures that the gas temperature leaving the brick matches the calibration data. Edit the duct settings and click on the Coefficients tab to set the Heat Transfer value to 5. On the Initial Conditions tab, set the Pressure to 1.05 [bar], the Fluid Temperature to 1100 [K], and the Wall Temperature to a constant named {CAT_TEMP}. When prompted to add CAT_TEMP to the Constants Table, click Yes and enter the values as shown in Figure 7.

Figure 7: Catalyst Brick Wall Temperatures

When completed, the model should appear as in Figure 8.

Figure 8: Model with Catalytic Converter

Save your model Click on the Save button in the toolbar

to save the file.

Proceed to 3. The Resonator (Silencer)

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SI Tutorial, Phase 5 - Adding the Exhaust System and Creating Spatial Plots in WavePost Step 3 - The Resonator (Silencer) The resonator is simply a perforated tube with a larger, concentric tube (can) around it. The resonator acts as a muffler and dampens certain frequencies in the exhaust stream. The resonator is modeled in WaveBuild as a series of complex y-junctions connected by massless ducts.

Chapter sections

Example Input File:



3.2 The Down Pipe


3.3 The Resonator



The schematic of the down pipe (from the catalytic converter) and resonator is shown in Figure 1. In WaveBuild, the down pipe can be modeled as two curved ducts and the resonator can be modeled as entry and exit ducts with Complex Y-junctions representing the entire length of the inner, perforated duct and the surrounding can.

Figure 1: Down pipe and resonator schematic

3.2 The Down Pipe

Drag and drop two orifice elements onto the canvas as shown in Figure 2, to represent the ends of the ducts used to model the downpipe. Draw the ducts representing the down pipe starting from the exit cone of the catalytic converter.

Figure 2: Down pipe junctions

Enter the geometric properties as shown in the schematic in Figure 1. Include a 90° Bend Angle for each duct and remember to use a Discretization Length of 40 [mm]. Set the Initial Conditions to 1.05 [bar] Pressure and1000 [K] Fluid Temperature with 800 [K] Wall Temperature. If desired, use control points to represent the bend angle on the canvas. With the down pipe modeled, the canvas should appear similar to Figure 3.

Figure 3: Down pipe ducts

3.3 The Resonator

The resonator is modeled with a short entry duct (40 mm long as shown in Figure 1), Complex Y junctions representing the inner perforated duct and the surrounding can, and a short exit duct. The completed WaveBuild representation of the resonator appears in Figure 4.

Figure 4: Resonator representation

The number of consecutive Complex Y-junctions to use can be determined by dividing the total length of the can (300 mm) by the exhaust discretization size (40 mm). The results in 7 Complex Y junctions used in series to represent the inner perforated duct and 7 more used to represent the surrounding can. The easiest method for building this resonator model is to build and define the first Complex Y-junction for the inner duct and outer can each, and then copy/paste them 6 times. The first Y-junction representing the inner perforated duct is cylindrical -- 42.857 mm long (300mm/7) and 50 mm in Diameter . This means it has a Volume of 84149.8 [mm 3] The Heat Transfer/Skin Friction Area can be calculated from the area of the pipe minus the area of the perforates connecting to the outer can. The area of the perforated section of pipe is 47123.89 mm 2. The total area of the perforates account for 20057.5 mm 2. Assuming the perforates are evenly distributed along the entire length of the pipe, we can calculate the surface area of a single Y-junction as 1/7th of the total surface area. Thus, the total Heat Transfer/Skin Friction Area for the single Y-junction is 3866.63 [mm 2]. Set the Initial Conditions to 1.05 [bar] Pressure, 900 [K] Fluid Temperature, and 700 [K] Wall Temperature. The Y-junction panel and pipe orientations should appear as in Figures 5 and 6.

Figure 5: Inner, perforated pipe y-junction

Figure 6: Inner, perforated pipe y-junction orientation

The first Y-junction representing the outer can is cylindrical as well, with the volume representing the inner duct subtracted (don't forget to include the 1 mm thickness of the tube wall). This creates a torus, or doughnut-shaped volume, with an equivalent Diameter of 108.15 [mm]. The resulting Volume is 393686.4 [mm 3] The Heat Transfer/Skin Friction Area of the entire outer can, including the end-caps can be averaged over all seven Y-junctions, and is 18781.3 [mm 2]. Set the Initial Conditions to 1.05 [bar] Pressure, 800 [K] Fluid Temperature, and 600 [K] Wall Temperature. The Y-junction panel and pipe orientations should appear as in Figure 7 and 8.

Figure 7: Outer can y-junction

Figure 8: Outer can y-junction orientation

Copy/paste the two Y-junctions to create seven of each, in series as shown in the figure below. All of the Y-Junctions representing the inner, perforated pipe should be connected by massless ducts with Diameters of 50 [mm]. All of the Y-junctions representing the outer can should be connected by massless ducts with Diameters of 108.15 [mm]. And each inner, perforated pipe Y-junction should be connected to the adjacent outer can Y-junction by amassless duct which represents the perforates, with a Diameter of 11.3 [mm] and a Count of 28.57 (=200/7, assuming they are evenly distributed).

Figure 9: Connectivity using massless ducts


to save the file.

Proceed to Step 4 - The Complex Muffler

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SI Tutorial, Phase 5 - Adding the Exhaust System and Creating Spatial Plots in WavePost Step 4 - The Complex Muffler (Optional) The complex muffler is a complicated portion of any WAVE model. It usually consists of multiple pipes, possibly perforated, passing through internal baffles within a large complex-shaped volume. It may have packing material made of rock wool or fiberglass in portions of the volume, used to dampen acoustic transmissions. Due to the complexity and tediousness of modeling this muffler, it is NOT mandatory for you to build it, but it is recommended that you understand the idea behind it and appreciate the need for a routine engineering tool to automatically mesh and generate a WAVE input file for such complex components. Fortunately, Ricardo Software has developed such a tool – named WaveBuild3D. WaveBuild3D is especially useful for auto-meshing intake and exhaust components for NVH applications. For more information about this tool, please contact your Ricardo Software Sales representative at (734) 394-3860 or via email at [email protected].

Chapter sections

Example Input File:



4.2 The Mid-Pipe Example Output File: 4.3 Modeling the Muffler in Quasi2D



The schematic of the mid-pipe and complex muffler is shown in Figure 1. In WaveBuild, the two segments that represent the mid-pipe can be modeled simply as two ducts, starting from the orifice junction at the end of the resonator. The complex muffler will be modeled as a series of inter-

connected Complex Y-junctions, massless duct connections, and normal ducts for the muffler entrance and tailpipe.

Figure 1: Mid-Pipe and Complex Muffler Schematic

4.2 The Mid-Pipe

Drag and drop two orifice elements onto the canvas as shown in Figure 2, to represent the ends of the ducts used to model the mid-pipe. Draw the ducts representing the mid-pipe starting from the orifice junction at the exit of the resonator.

Figure 2: Mid-Pipe Junctions

Enter the geometric properties as shown in the schematic in Figure 1. Include a 90° Bend Angle for the first duct and remember to use a Discretization Length of 40 [mm]. Set the Initial Conditions to 1.05 [bar] Pressure and800 [K] Fluid Temperature with 600 [K] Wall Temperature. If desired, use control points to represent the bend angle on the canvas. With the mid-pipe modeled, the canvas should appear similar to Figure 3.

Figure 3: Mid-Pipe Ducts

4.3 Modeling the Muffler in Quasi-2D

Because the muffler is such a large and complex volume, the three internal chambers which physically divide the muffler vertically, as shown in the schematic, should be sub-divided and modeled with multiple Complex Y-junctions. Each section of perforated pipe will also have to be represented by Complex Y-junctions attached to the surrounding volume(s) with multi-count massless ducts to represent the perforates, as in the resonator . The level of refinement is up to the user and what kind of results they desire: for performance, simple Quasi-2D meshing may be sufficient but for acoustics, detailed Quasi-3D meshing should be performed. We refer to meshing in WAVE as "Quasi" meshing as it is not identical to full-scale 3-D CFD but can approximate the same results. Quasi-2D meshing (Box A in Figure 4) is sub-division of volumes in 2 axial directions (X and Y, in this case) and ignoring the division in the 3rd direction (Z axis). Quasi-3D meshing (Box B in Figure 4) is sub-dividing volumes in all 3 axial directions. The number of subvolumes increases dramatically between Quasi-2D and Quasi-3D meshing!

Figure 4: Modeling in Multiple Dimensions

The complexity of this connectivity of Y-junctions, massless ducts, and normal ducts has no uniquelycorrect design and different designers might end up with different connectivity matrices for this same muffler. Also, this modeling work has no real engineering value, it's only routine work that could to be automated! It is expensive and tedious for you, the engineer, to spend your time on such laborious tasks. For this reason, Ricardo Software introduced WaveBuild3D as an auto-mesher for large components in the intake and exhaust systems using a solid-modeling interface to represent the geometry. The table below shows a comparison for different mesh matrix sizes vs. pre-processing time of manual meshing (by you the user) and WaveBuild3D (computer program auto-meshing). * Based on average time an engineer spends to complete one complex Y-junction input = 6 minutes ** Based on meshing using Intel Core 2 Duo T7600

# of Subvolumes (Matrix Size)

Meshing Type 2D/3D

# of Repeated Tasks

Engineer Minutes*

WaveBuild3D Minutes**

3x3

2D

18

108

0.03

3x3x3

3D

54

324

0.05

9x9x9

3D

1458

8748

0.37

15 x 15 x 15

3D

6750

40500

0.83

nxnxn

3D

2 x n3

2 x n3 x 6

–

It is left to you, the new WAVE user, to complete modeling the muffler. At this point there is nothing new to learn. All that needs to be done is repeating the geometric and duct orientation input many times to model the muffler as a network of ducts, massless ducts, and Complex Y-junctions. The muffler is shown in WaveBuild3D in Figure 5 and the corresponding WAVE mesh is shown in Figure 6.

Figure 5: Muffler in WaveBuild3D

Figure 6: Muffler mesh from WaveBuild3D

The WaveBuild3D tool creates portions of WAVE models known as Components. Any WaveBuild3D component can be used in any WAVE model, regardless of whether or not the user has a WaveBuild3D license. This muffler component is shipped as an example model. To add it to the model, expand the Tags branch under the Components branch of the Elements tree. Drag and drop the SI_Muffler component onto the canvas and connect it to the model by attaching the last duct of the mid pipe (the last orifice element can be deleted, as it is no longer necessary) to the inlet connection point of the component. Connect the outlet connection point of the muffler component to the Exhaust ambient using a duct with 50 [mm] diameters and an overall length of 40 [mm] (use initial conditions similar to the mid-pipe). When finished, the model should appear similar to Figure 7.

Figure 7: Completed Model in WaveBuild


to save the file.

Proceed to Step 5 - Creating Spatial Plots in WavePost

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SI Tutorial, Phase 5 - Adding the Exhaust System and Creating Spatial Plots in WavePost Step 5 - Creating Spatial Plots in WavePost WavePost can use time-based data to create plots of scalar/vector quantities along a length of the network to observe traveling pressure waves, temperature profiles, etc. These spatial plots can be animated to observe the temporal change in WavePost and saved as .mpg files for use in presentations and reports.

Chapter sections

Example Input File:

5.1 Creating

.\Ricardo\WAVE\8.0\examples\engine\TUT_si\tut_si4_intake.wvm

Spatial Plots in WavePost 5.2 Animating Spatial Plots


.\Ricardo\WAVE\8.0\examples\engine\TUT_si\tut_si4_intake.wps

5.1 Creating Spatial Plots in WavePost

Run the WAVE model by clicking on the Run Screen Mode button in the toolbar (if prompted to save the model before running WAVE, click the OK button to save and run sequentially). Launch WavePost from WaveBuild by clicking in the Launch WavePost button in the WaveBuild toolbar . This will open the .wps file named similarly to .wvm currently loaded in WaveBuild. Once WavePost is open, click the Open File button in the toolbar and open the .wps file created in Phase 3, Comparison.wps . This WavePost session file is currently referencing results from the 4-cylinder model without intake/exhaust ( tut_si4) and from the four-cylinder model with intake only (tut_si4_intake ). It should contain sweep plots created during the in Phase 3 of torque, power, etc. Click on the Add button at the bottom of the Output Files frame and select the newly wvd file for the WAVE model containing both the intake and exhaust systems created . (tut_si4_exhaust). The .wvd and .sum files for this W AVE run will be added to the Output Files list. A Query window will pop-up prompting whether to add curves to the existing plots using this file. Click on the Yes button and every existing plot will add data from the newly added.wvd and .sum files (if matching data exists in the new files). Open the Sweep Plots to view the comparison of the performance parameters. On the Canvas of the WavePost GUI, use the Shift+Left Click to multiple-select the ducts and junctions along the intake runner to the cyl1 junction (see Figure 1). Right-click on one of the ducts/junctions in the highlighted group and select the " Add Spatial Plot > Basic > Pressure" menu item, as shown in Figure 2.

Figure 1: Ducts and Junctions for Spatial Plot

Figure 2: Adding a spatial plot via the context menu

A Spatial Plot of the pressure along this path will be automatically created, showing a scaled view of the ducts/junctions along the path and the pressure profile in those ducts/junctions on the same plot (see Figure 3). Therepresentation of the ducts/junctions can be moved using the middle mouse button or removed from the plot altogether by double-clicking on it and de-selecting the Display Scale View option, where the crank animation can also be displayed (also accessible from the Tools > Display pull-down menu item).

Figure 3: Spatial Plot Display Panel

Figure 4: Spatial Plot of Pressure in Runner 1

5.2 Animating Spatial Plots

Spatial Plots can be anim ated just like canvas displays of network variables, as demonstrated in Phase 4. Simply open the Animation Panel by selecting the Animation... menu option from the Tools pull-down menu (seeFigure 5). The animation can be played or recorded to a MPEG file for use in reports/presentations. The Time Offset can be set to change the starting point of the animation, allowing multiple spatial plots to be shown in/out of phase.

Figure 5: Spatial Plot Animation Panel

The Animated Spatial Plot should appear as the video at the bottom of the page.

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