The powertrain design software and CAE newsletter of Ricardo Characterizing the Range Rover and Range Rover Sport using WAVE Jaguar Land Rover’s Simon Worledge of the Powertrain NVH department faced a challenge when designing different sound signatures for the Range Rover and Range Rover Sport, both of which share the same drivetrain architecture. WAVE software helped tackle the problem Virtual engineering in the form of CAE software has been with us for some time now and it is a given that systems are modelled prior to physical prototyping, saving time and money. Yet despite the relative maturity of simulation techniques, it is an area of engineering which continues to develop. This is partly due to the improved functionality of software but also because simulation is a voyage of discovery where experience plays a big part in exploiting the power of software tools to the fullest. At the Ricardo Software European User Conference held in Ludwigsburg, Germany, in April of this year, Simon Worledge of Jaguar Land Rover Powertrain NVH gave an overview of how exhaust systems were developed for the new Range Rover and Range Rover Sport models using WAVE. One platform, two very different vehicles Prior to the introduction of these new-generation cars, the outgoing models were actually quite different entities in that the Range Rover Sport was not based on the Range Rover, but the Land Rover Discovery. In contrast, both of the new vehicles are based on the company’s D7u platform which in turn, is part of Jaguar Land Rover’s Premium Lightweight Architecture. Both the Range Rover and Range Rover Sport have all-aluminium bodyshells where the previous vehicles were built from steel. The new models are not only the largest automotive aluminium bodyshells in the world but each side panel is the largest one-piece single aluminium pressing used on any passenger vehicle worldwide. The vehicles are both completely different to their predecessors structurally, the Range Rover weighing 420 kg less than the outgoing model. The outgoing vehicles In this Issue The new Range Rover Sport (right) and Range Rover (page 3) are based on the D7u platform – a key challenge for the NVH team was to provide the required sound quality and differentiation from a common exhaust layout Pages 1-3 Sound quality How Jaguar Land Rover used Ricardo WAVE software to create the right sound for the Range Rover and Range Rover Sport Pages 3-4 Exhaust vibration Independent engineering specialist Martin Unbehaun uses WAVE and FEARCE to eliminate unwanted vibration from gas excitation Pages 4 Application Engineering Ricardo Software launches a new service to help licensees maximize their effectiveness and return on investment in CAE ww.ricardo.com/SCAE • Subscribe free at www.ricardo.com/SCAE • Subscribe free at www.ricardo.com/SCAE Issue 1 2014 Software&CAE Range Rover and WAVE Range Rover Intermediate Can Fully developed CAD model Broadband high frequency attenuation of engine "crackle" – mainly empirical development after WAVE confirmed unnecessary for order control WaveBuild3D model The modelled perforated baffle had minimal acoustic benefit compared to the requirement to exclude any pack material from the slipjoint area shared common power units, the flagship being the V8 5.0 supercharged engine, but both were equipped with unique exhaust systems with intrinsically different sound quality and character. A key requirement for the two new vehicles was product differentiation. As both share not only the same architecture but the same exhaust layout, this was to prove a challenge. Both vehicles have very different characters, something that should be reflected in their sound signatures. The Range Rover represents the pinnacle of refinement but the Range Rover Sport, while remaining luxurious and refined, needed that edge to the exhaust note befitting a sports vehicle. The Land Rover engineering teams work according to quite specific character definitions given to individual vehicles. In this case, the Range Rover should have “effortless delivery of power with imperious isolation,” while the Range Rover Sport should convey a character that is “direct, powerful and purposeful.” Sound engineering The NVH teams translate these messages into hard technical facts. At the higher rev ranges, the Range Rover has no requirement to produce a ‘crisp, edgy crescendo’ whereas the Range Rover Sport does. At lower engine speeds the Range Rover has a complete absence of booms but gives a subtle acoustic ‘reward.’ The Range Rover Sport, on the other hand, is quite different at the low engine speed range with dominant fourth and subfiring orders giving a ‘burble and an overt promise of performance.’ Initial concepts were based on muffler boxes derived from Jaguar luxury saloons. Although performing well in the original saloon applications, WAVE analysis soon revealed that the designs would not be an ideal match for the bigger cabin space of the SUVs. “When we finally got hardware produced, it wasn’t quite what we needed. The back box was fairly complex with a bypass valve, we had flow issues and it was inherently prone to high frequency broadband gas rush noise which didn’t give the impression of refinement,” explains Worledge. Simulations for the front box produced sounds that were too unrefined and the small gap for mixing gas between chamber and pipe produced unsatisfactory levels of back pressure. With that much established, it was back to the drawing board, starting with the basics to examine the underlying order structure and the extremes of available tuning options. With V8s, Jaguar Land Rover focuses on four primary orders for target setting and engineering: 1.5E, 2.5E, 4E and 8E. Because the engine is a V8, 4E will always be dominant but increasing the ’half’ order content would give the Range Rover Sport exhaust note the more complex character it needed. “We control this feature by how we mix the gases early in the system,” explains Worledge. Starting with the Range Rover and taking a fully mixed approach, a new and bigger front can of 4.9-litre capacity was created in WaveBuild3D then fully developed as a CAD model. Significant work was done using CFD to optimize the main duct and minimize back pressure. The addition of a small Helmholz resonator on the main central duct proved useful, attenuating a fourth order peak quite dramatically by around 10dB(A). “Although in the WAVE model an intermediate can was not needed, in physical testing the use of one showed promise for mid to high frequency attenuation so we kept it in place for completeness,” continues Worledge. The can was designed using the same techniques and was much simpler than the front unit with two parallel perforated pipes. The rear can was a much simpler design than the very first model based on Jaguar designs, with a ‘Perf ‘n’ Pack bomb – a chamber filled with absorptive packing material, through which the main exhaust line passes – at its centre to deal with high frequency noise and flow noise attenuation. A long, relatively small diameter tailpipe gave good low frequency attenuation and a pressurised Helmholz resonator helped with specific boom control. “This resonator gave significant fourth order control at low cruising speeds and this extrapolates back to low rpm, giving a high level of refinement in the idle region and no unpleasant booms in the cabin,” says Worledge. When the finished results were compared to the WAVE predictions, the correlation, though not perfect on three orders, matched well on the fourth. “I have a suspicion that the lack of correlation is due to the high level of packing in the centre box,” explains Worledge. The results are measured using a microphone positioned 500mm from the tailpipe at an angle of 45 degrees to one side. The virtual microphone is mounted in the same position within WAVE. A more sports-like sound quality The Range Rover Sport required a different approach to reflect the vehicle’s sportier character. Two cans, front and rear, were modelled in WaveBuild3D with no intermediate can. Again, the capacity of the three-chamber front can was 2 Ricardo Software & CAE • Issue 1 • 2014 Range Rover and WAVE / Exhaust Vibration A more radical version was tried too, the front box having the stainless steel wool removed from one chamber and five 3.5 mm mixing holes added to each duct in the centre chamber. These perforations softened the effect slightly, the sound otherwise lacking subtlety. Underfloor pipes were increased in diameter to 60 mm. The rear box retained the basic form but was given two tailpipes and a more conventional resonator. One tailpipe incorporated a butterfly valve allowing the exhaust to demonstrate a duality to its signature. 4.9 litres but instead of full mixing, two ducts ran straight through in parallel, giving an unmixed system. The first and third chambers were packed with stainless steel wool and each duct perforated at the opposite end from the other (one perforated in the first chamber and the other in the third). In the rear can, the Perf ‘n’ Pack bomb was deleted and the effectiveness of the Helmholtz resonator reduced by decreasing the size of the neck. The tailpipe diameter was increased to 75 mm. In contrast to the Range Rover, it was desirable to retain the order content coming through and for it to be audible from the tailpipe. Using WavePost’s Frequency Network Display, Worledge identified a 600 Hz mode across the front chamber of the rear box: this gave a much stronger resonance at the exhaust orifice than the initial attempts, which centred only on tuning the tailpipe length, resulting in the crisp definition of the sound character. On this occasion, the physical performance of the finished system correlated closely with the WAVE predictions indicating just how powerful WAVE can be in early simulations. With the valve closed for relaxed cruising, the exhaust gas exits the first pipe into a chamber via perforations and exits via the second tailpipe, a resonator helping to attenuate the sound. With the valve open, the system becomes effectively 'straight through', emphasising the low frequency range around the 1.5 and 2.5 orders, giving a rich, deep, modulated sound. However, this version was judged to be too extreme for a mainstream product, and has been held in abeyance pending a more suitable vehicle package. Nevertheless, the other designs formed the basis of the new Range Rover line-up’s sound signatures, helping to make them among the most desirable premium vehicles in the world. Beating exhaust vibration with WAVE and FEARCE Gas excitation can cause deformation and unwanted vibration in exhaust systems. Independent engineering specialist Martin Unbehaun has discovered how to address this issue for his clients using a unique approach and Ricardo Software technology Quite where vibration comes from in a vehicle exhaust system is not always clear, but Martin Unbehaun of Unbehaun Acoustic Engineering has been looking at how a combination of WAVE and FEARCE can be used more effectively than traditional methods to measure an important aspect of exhaust system design that has so far remained overlooked. Traditionally, CAE analysis of exhaust systems has focused on temperature, back pressure and tailpipe noise using WAVE, detailed flow distribution using 3D-CFD, deformation and stresses arising from heat Issue 1 • 2014 • Ricardo Software & CAE 3 Exhaust Vibration strain, and road excitation and engine vibration, using FE methods. But the one area that has been overlooked until now has been that of deformation and stresses caused by exhaust gas excitation. “One day we found very strong vibrations in an exhaust system at engine order 1.5 with a V6 engine,” explains Unbehaun. “The engine had almost no vibration at that engine order but the exhaust system itself had strong vibrations of up Martin Unbehaun to six millimetres downstream from the flexible coupling.” A V8 exhaust system was prepared with short exits at the bottom of the downpipes. Vibration further down the system disappeared, supporting the theory that the vibration was caused by gas flow. Three parameters were singled out for investigation: average pressure, pulsating pressure and pulsating flow. Measurements at the centre of the muffler revealed an average pressure of 400 mbar. When multiplied by the area, this extrapolated to a force of 5000 N, or the equivalent of hanging a 500 kg weight from the muffler. Pulsating pressure was identified in curved sections of pipe (such as the downpipe) equivalent to 145 N; a great deal of force. Finally, pulsating flow velocities of 220 m/sec were identified, creating forces in a curved pipe of 50 N. The classical approach for measuring this was to use WAVE and an FE simulation. The system took the form of twin pipes leaving the engine and entering a centre muffler, a single pipe exiting to a rear muffler. The simulation showed exhaust gas entering the centre muffler from one bank of cylinders, trying to exit back in the opposite direction via the second branch of the system, giving a very strong resonance in the process. The forces can be calculated by exporting the pressures and velocities into a spreadsheet. The simulation was performed for steady and transient states to calculate the level of excitation, a process which requires much thought and hard work. The new method adopted by Unbehaun is to apply the WAVE temperature and pressure results to the FE model in FEARCE by exporting to a cloud file. The simulation produced a strong vibration of up to 3.5 mm, which corresponds to the measurements found in a similar physical system. The next stage was find out how best to minimize the vibration. With an open bridge linking the two pipes at the front of the system, the gas resonance bypasses the main system and the excitation is eliminated. The method was also applied to assessing the effect of sound radiated from the muffler due to vibrations. A combination of the changed muffler shape and the open bridge significantly reduced vibration and radiated noise. It is early days yet, but the results are extremely promising and Unbehaun is looking forward to exploiting this new WAVE- and FEARCE-based technique in his future client work, and correlating results in more detail with physical testing. Bespoke CAE support Ricardo Software has launched a new ‘Application Engineering’ service to help its software licensees maximize their effectiveness and return on investment in CAE simulation. The service has two distinct facets: helping customers improve their deployment of CAE through analysis process development, and the execution of small simulation projects using Ricardo Software products in order to demonstrate different applications on live design, development or research tasks. “Customers are frequently telling us that they’d appreciate support beyond the level of the conventional user training model,” explains For further information about Ricardo Software productions and support services, please contact: application engineering manager John Foy. “As the developer of the CAE products and a major consulting business in its own right, Ricardo is ideally placed to provide highly trained and experienced engineers to demonstrate complex applications or to configure CAE processes designed around the specific needs of individual clients.” The benefits of this form of service can be considerable, not least in exploring the possible use of new software products or applications. “The traditional approach to evaluating a new product is to take an evaluation licence and allow engineers who are unlikely to be Software Sales: Software Support: Or visit experienced in its use to make an evaluation,” continues Foy. “We can work with the client before this stage, to assess precisely the CAE products that will best suit their requirements, and then demonstrate the software on live projects. For a small investment, the client can be up and running much more quickly and can potentially yield a much better return on their CAE investment,” he concludes. The Application Engineering service is available across the full range of Ricardo Software CAE products. For further information contact John Foy at [email protected]. [email protected] [email protected] www.ricardo.com Subscribe free at www.ricardo.com/SCAE • Subscribe free at www.ricardo.com/SCAE • Subscribe free at www