Advances in Core CFD Technology: Meeting Your Evolving Product Development Needs

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1 White Paper Advances in Core CFD Technology: Meeting By Eric Bish, Ph.D. Software Development Manager ANSYS, Inc. Product developers may see it as a perfect storm of challenges: increased product complexity, tighter quality requirements, and higher yield and productivity indexes. Even with such constraints, today s most successful companies are bringing game-changing products to market. Consider these outside-the-box ideas that are now realities. Dyson s acclaimed new fan that eliminates blades along with associated buffeting and turbulence Chevy Volt, an electric car that boasts some of the most advanced engineering ever seen in a mainstream American automobile For over 25 years, engineers have leveraged fluid dynamics advances to bring innovative products to market faster, more cost effectively and more efficiently. Today, CFD tools must evolve to address future engineering design needs. Terrafugia s Transition Roadable Aircraft, which has a flight range of up to 490 miles and land cruising speed of 105 mph Apple s ipad and iphone, which have revolutionized the way we communicate Speedo s LZR RACER swimsuit that helped world-class swimmers at the Beijing Olympics set new world records What engineering design tools helped speed these products to market ahead of the competition? How did developers ensure that designed-in features would function as expected under real-world conditions? One of the key factors common to these products is computational fluid dynamics, or CFD. For over 25 years, engineers have leveraged fluid dynamics advances to bring innovative products to market faster, more cost effectively and more efficiently. And as end products become even more intricate, as consumers and governments demand optimized performance to meet environmental targets, CFD tools must also evolve to address future engineering design needs. For example, heightened product complexity will demand greater depth in physics models (such as turbulence, chemistry, particulates, real-fluid properties), physics breadth (structural mechanics, fluid dynamics) and coupling (for example, flow-induced deformation). More intricate designs will require transient analysis of moving parts (such as impellers, valves and pistons). Not just any design will serve: It must be the optimal design. And not just any CFD tool will serve. Technology with limited scope cannot sustain present let alone future engineering design needs. Continued advances in core CFD technology especially in the critical areas of solution fidelity and speed, optimization, and robustness and usability promise to offer innovative solutions to meet evolving product development needs. 1

2 Overall CFD Benefits CFD technology is a proven and sophisticated computationally based design and analysis technique. It aids in building a virtual prototype of the system or device, ultimately providing images and data that predict the performance of a particular design. From a top-down perspective, there are solid business reasons to use CFD analysis. CFD cross section of unique fan ring design showing contours of velocity magnitude. Dyson, a U.K. product innovator, used software from ANSYS to develop its acclaimed Air Multiplier. Insight: Applicable to any device or system design that is difficult to prototype or test through experimentation, CFD analysis enables virtual interrogation to see how a given design performs. There are many phenomena that CFD can capture some of them cost prohibitive or simply impractical to investigate any other way. CFD provides deeper insight into designs. Foresight: Because CFD is a tool for predicting what will happen under a given set of circumstances, it can readily answer what-if questions. The user provides a set of boundary conditions, and the software produces outcomes within a short time. The data can be used to predict how the design will perform, with the ability to test many variations to reach an optimal result. CFD allows engineers to identify possible design flaws in the early stages of development, before more-costly physical prototyping and latestage testing. CFD tools help to minimize the risk of costly and potentially embarrassing product failures. CFD allowed Centro Richerche Fiat in Italy to save time and money by reducing wind tunnel experiments. Use of ANSYS fluid dynamics technology during the design cycle of the fuel-efficient Fiat Panda MultiEco was instrumental in reaching aerodynamic goals. Productivity: The foresight gained from CFD helps users to design better and faster, save money, meet environmental regulations, and ensure industry compliance. CFD analysis leads to shorter design cycles and accelerated new product development. In addition, changes to existing equipment can be built and installed with minimal downtime. CFD is a tool for compressing the design and development cycle, allowing for rapid prototyping. CFD as a Catalyst for Continued Innovation Product development organizations today turn to CFD technology to help deliver ever greater efficiencies in bringing the next world-class products to market. In the future, commercial CFD software must meet and exceed requirements of depth, breadth and scalability with greater reliability and without application barriers. This holistic view will enable tomorrow s CFD practitioners to leverage CFD technology in unprecedented ways while simultaneously managing product development risk and optimizing factors that impact production time, cost and final product quality. 2

3 Continued advances in core CFD technology in critical areas promise to offer innovative solutions to meet industry s evolving and increasingly demanding product development needs. There are three compelling technology reasons to use CFD as an R&D solution: accuracy and speed, optimization, and robustness and usability. Tractebel in Brazil simulated a coal burner with ANSYS software to identify contributing erosion. The company estimated that the altered design will reduce boiler downtime from once every three years to once every five years. As products grow more sophisticated, so do companies requirements for engineering simulation tools. A decade ago, Zitron in Spain solved the characterization of a simple ventilation circuit under steady-state conditions using CFD tools from ANSYS. Today, all heat transfer modes including spectral radiation and species combustions are considered in a transient manner to accurately assess the time response to Zitron s ventilation management system in the event of fire in a tunnel several kilometers long. Solution Accuracy and Speed CFD solutions must produce more-accurate results for more-realistic virtual prototypes. Greater fidelity allows the engineer to explore increasingly realistic designs, which contribute greatly to making important design decisions. Essential to improved accuracy are advances in numerical algorithms and mainstream use of higher-order discretization methods. In many cases, proper modeling requires the ability to predict the dynamic behavior of the flow field as a function of time. As time-dependent solution methods become more accurate and efficient, transient CFD solutions will become an intrinsic part of day-to-day product development. The ability to simulate models with moving parts in applications such as turbomachinery (pumps, compressors, turbines), mixing tanks, valves and reciprocating machines like IC engines has become more commonplace in many industries. CFD offers product developers in these areas the potential for greater realism in simulation. CFD s numerical models virtually represent all the physics happening in a process or device in reality. More sophisticated and accurate physical models will drive more-authentic CFD simulations that can reveal new levels of insight into product designs. Turbulence and multiphase modeling are ubiquitous in fluids engineering simulation; these continue to be active areas for further research and development. And though added complexity sometimes leads to longer turnaround time, engineers don t have to make tradeoffs: The best CFD software suites offer both speed and accuracy, which are enabled by the specialized advancements made in CFD core technology. Commercial CFD software must also produce results robustly and in a minimum amount of time. More-efficient solution algorithms for both steady-state and transient CFD simulations are essential. High-performance computing (HPC) and parallel computing have become indispensible enabling technologies. Continued optimization of CFD algorithms for peak scalability will enable organizations to leverage hardware technology and peripherals advances for multi-core machines and distributed cluster networks. Solution-steering techniques can help in automatically selecting and adjusting solution settings for improved solver robustness and performance with less babysitting. In addition, emerging advances handle solution instabilities, especially on low-quality meshes. Solution sensitivity analyses have the potential to improve the process by identifying optimal choices for input parameters, such as boundary conditions, solution controls, time steps and local mesh density. 3

4 Blade flutter with compressors and turbines is a serious cause of machine failure. Until recently, it has been beyond the design capability to satisfactorily investigate and avoid this phenomenon. Bidirectionally coupled CFD and structural tools from ANSYS can now predict vibration modes that occur over an entire wheel from a single-blade component model. Fluid structure interaction accurately predicts how a design will function in a real-world environment. Courtesy PCA Engineers Ltd. Advanced turbulence models offers tools that eliminate the tradeoffs between speed and accuracy. Zonal RANS-LES models in ANSYS software enable the user to define LES only in the region where it is needed for highest accuracy, while RANS is used to model the remaining region. This enables design teams to speed up the computation while maintaining a high accuracy in regions of highest interest. Solution Optimization CFD solutions must allow an engineer to easily and seamlessly explore a wider parameter space for design optimization. Traditionally, exploring optimal design configurations has involved computing individual solutions to a set of strategically chosen configurations representing points in a parameter space. The variation in key engineering output quantities for the system are mapped as a function of input conditions to help target an optimized configuration that can be further explored and refined. The sensitivity of product performance to off-design conditions can also be considered. Typically, however, only a limited number of input/output parameters and cases can be included in the analysis for time and cost reasons, making the entire process prone to error and highly dependent on the expertise of the engineering team. The ability to optimize designs for new products without the benefit of past operational experience can be prohibitively costly. New methods for determining the derivative of a CFD solution with respect to input parameters using the solution of adjoints have the potential to take design optimization to a powerful new level. An adjoint solution is able provide the derivative of an engineering observation (for example, lift, drag or total pressure drop through a system) with respect to a very large number of input parameters simultaneously via a single computation. The adjoint solution can be used to guide the optimal adjustment that will improve a system s performance as part of a gradient-based optimization algorithm. An adjoint solution can be used to estimate the effect of a change prior to actually making the change. The derivatives with respect to the geometric shape of the system can also be determined. Sensitivity data derived from these gradients can be combined with mesh morphing, for example, to guide smooth mesh deformations for shape optimization. Automation of optimization tools into the CFD workflow from initial concept to final design is essential to leveraging these techniques to their greatest advantage. Solution Robustness and Usability Engineers must be able to rely on CFD simulation to help guide increasingly complex and critical product development decisions. Continuous improvements in coding practices, along with comprehensive code verification and validation, are needed to ensure high-quality reliable code. Code defects are a leading risk factor; they can have a significant negative impact on the effectiveness of CFD simulation in product development. Defects can slow the pace of product development and lead to additional project costs in terms of work hours and unrealized productivity. When problems do occur, support organizations must be ready to help mitigate the immediate impact and deliver a solution in a timely manner. 4

5 Therefore, CFD code quality must be an ongoing priority for code vendors. Much good has been done and is expected for the future with the adoption of quality standards such as ISO-9001 and NQA-1. The adjoint solver in ANSYS software provides specific information about a fluid system that is very difficult to gather otherwise. This vector plot of an internal combustion engine s inlet port shows sensitivity of geometry shape to pressure drop, created using the adjoint solver in ANSYS software. The vector direction and magnitude indicate the recommended geometry change to improve the design. For CFD simulation to have it greatest impact on the design process, it should go beyond serving as a predictive tool for a given configuration and set of conditions. It must also shed light on the relative goodness of any given solution. One promising approach is to estimate the solution error using sensitivity analyses. With this process, the reliability of a design can be investigated along with the sensitivity of a design to variations in operating conditions. Sensitivity analyses can be used to assess tradeoffs in a set of plausible designs. CFD technology provides even greater value when it is more widely accessible within product development organizations. Democratizing simulation for wider deployment requires that CFD codes be more reliable. Intuitive and easy-to-use interfaces are making it possible for more engineers with little CFD experience to effectively utilize simulation as a value-added engineering tool. Expert users need to be able to collaborate with others to share knowledge and increase productivity. The integration of CFD simulation with other physics disciplines such as structural mechanics and electromagnetics is already under way. Further development will open even more windows of opportunity to leverage CFD simulation in product development organizations. Robust CFD tools are especially critical when the ability to perform physical testing is limited. In designing pulse jet mixers (PJMs) for use in converting nuclear plant radioactive waste into stable, storable materials U.S.-based Bechtel National engineers needed sufficient confidence that their fluid flow model would provide pass fail judgments. Software from ANSYS enabled them to accurately predict the ability of the units to provide sufficient mixing for each of the different vessels in which the waste would be treated. This image shows contours of solid particle concentration. During the suction phase, the solids were found to become more concentrated along the bottom of the vessel, as shown by the red color in the early suction. ANSYS, Inc. Southpointe 275 Technology Drive Canonsburg, PA U.S.A ansysinfo@ansys.com Toll Free U.S.A./Canada: Toll Free Mexico: Europe: eu.sales@ansys.com ANSYS combines the most respected names in fluid simulation ANSYS FLUENT and ANSYS CFX to expertly address evolving CFD needs at a time when product reliability, safety and market performance are paramount. ANSYS offers the most complete suite of advanced CFD software tools available, coupled with unrivaled modeling capabilities, to help you achieve a faster total time to solution. Product development leaders worldwide trust ANSYS software as their fluid dynamics simulation platform for its accuracy, reliability and speed ANSYS, Inc. All Rights Reserved. For more information, visit: