when we think of CFD (computational fluid dynamics) in the aerospace and aeronautical industries, we often limit our thinking to the aerodynamic analysis of wing/tail structure or fuselages. But CFD analysis applies to almost all of the critical components and systems of an aircraft. For example, excessive heat in the electronic components can lead to failure and reliability issues. Fuel delivery and engine cooling systems must be optimized. Cabin air conditioning/heating systems need to be analyzed. And the industry cannot afford to either over-conservatively design these systems (excessive cost) or prove efficiency/reliability by building multiple physical prototypes, testing in labs, and then re-designing, which is a long and expensive process. Because of these issues, CFD comes into play early and throughout the design process for multiple components and systems in the aircraft.
Using CFD is no longer relegated to the realm of the specialist. A new class of CFD analysis software, “Concurrent CFD,” is proving to be highly effective at performing these analyses, enabling design engineers as well as specialists to accelerate key decisions at their workstations as they experiment with design scenarios and as they hone in on the best, most efficient, reliable, and cost-effective design. With CFD embedded into the MCAD environment, this intuitive process allows design engineers to optimize a product during the design stages; and that first physical prototype will often be the design that goes into final manufacturing.
Until recently, the commercial software available for CFD typically has been geared toward only the specialists, limiting its widespread use. Besides being expensive, these tools have been challenging to use. As a result, engineering analysis for applications such as pressure drop, heat transfer, fluid flow, etc. traditionally have been carried out only by CFD specialists in analysis departments, separate from mainstream design and development departments. This limited the number of design approaches tested and taxed the overburdened specialists.
Fortunately, new tools have emerged that embed a complete range of flow analyses within mainstream MCAD toolsets such as CATIA® V5, PTC Creo®, and Siemens NX™. For example, the FloEFD™ design/ analysis technology offered by Mentor Graphics is specifically targeted at the design engineer as well as the specialist. It has the combination of simulation accuracy plus the ease-of-use and speed needed to be used as an integral part of the design process.
With these new CFD tools, a design engineer with standard training and working in any size company can use his or her existing knowledge to successfully perform analyses, all within the familiar MCAD environment of choice. Certainly, there will always be a few very demanding applications where more advanced CFD knowledge is needed to fine-tune the meshing and solver settings to converge to a solution. However, taking CFD out of the exclusive domain of specialists and bringing it into the mainstream enables design engineers with little specific training in CFD to analyze problems in roughly 80 to 90% of the time compared to using traditional tools. This offers designers a fundamental breakthrough in design efficiency.
Characteristics of CFD Targeted at the Design Engineer
For example, some CFD simulation software provides a complete environment for performing analysis such as heat transfer by combining all the phases of analysis in one single package: from solid modeling, to problem set up, running, results visualization, validating the design, and reporting. Figure 1 illustrates some of the important characteristics of CFD software that enables it to be useful to design engineers and not just specialists.
MCAD system embedded
All the designer needs is knowledge of the MCAD system and the physics of the product to use next-generation CFD. After installation, all the menus and commands necessary to run a full CFD flow analysis are created in the MCAD package’s menu system. This CFD embedded within the MCAD system makes it extremely easy to use. The design engineer is already familiar with the menu structures. The CFD analysis tool uses the same GUI structures so the engineer does not have to learn a completely new interface (Figure 2).
The starting point of any heat transfer and fluid flow analysis is to define the overall boundary conditions of the problem. A wizard is available to direct the setup, including the selection of models. This lets a designer take advantage of existing MCAD models for analysis, without having to export or import additional data, saving significant amount of time and effort. The embedded CFD software can use newly created or existing 3D CAD geometry and solid model information to simulate designs in real-world conditions.
Automated cartesian meshing
Once a model is created, the model needs to be meshed. Developing a mesh is one of those skills that previously separated CFD specialists from mechanical design engineers. With FloEFD, meshes are created automatically in a matter of minutes rather than requiring hours of tedious proportioning of regions and cells. The software actually creates an adaptive mesh that reduces the cell size (increasing the resolution of the analysis) to ensure more accurate simulation results in complex areas of the model, as shown in Figure 3.
Easy-to-Use engineer oriented interfaces
Stepping through the analysis process can be very confusing to the non-specialist. However, with a next-generation CFD tool, the design engineer is stepped through the process by wizards that ensure all data such as materials, fluid characteristics, boundary conditions, and execution parameters are properly defined.
Multi-Variant parametric modeling
This feature enables the design engineer to set up a series of experiments and submit multiple analyses for batch runs. The engineer can define a range of values and then modify the design (number of fins on the heat sink, dimensions of an outlet, etc.) or boundary conditions (pressure, flow volume, temperature, etc.) across a spectrum. The software automatically generates a series of analysis runs and submits them for execution. The results of these experiments can be compared and visualized, and then the best design can be chosen.
Laminar-Turbulent transitional modeling
The modeling of a fluid flow is extremely complex while the flow transitions from laminar to turbulent or vice versa. In typical CFD software, this requires two different models and an understanding on the part of the engineer as to which one should be used. A model that senses this transition and automatically employs the correct modeling at the correct time in the transition eliminates the need for two different models and the intervention of the engineer (Figure 4).
Automated/Guaranteed convergence
One of the most difficult tasks even for the CFD specialist is to ensure that the CFD analysis converges. Many factors can contribute to a CFD analysis non-convergence. Model complexity, meshing, boundary conditions, etc. can all cause older-generation software not to converge. The specialist must then experiment, sometimes using trial and error, to urge the software into convergence. With software such as FloEFD, convergence is virtually guaranteed, thus eliminating the need for the design engineer to tweak the model.
These are just some examples of the technologies that enable complex CFD to be put into the hands of the design engineer as well as the specialist.
CFD Analysis from Complex Components to Systems
When we think of CFD analysis, we might limit our thinking to the individual components of an aircraft or satellite, such as the electronics in a navigation computer for proper heat management, the fuel flow through an injector, or the capability of an oil cooling component. We might not imagine, given the size and complexity of a complete system such as fuel delivery, that we could analyze it with all the feet of piping, pumps, valves, etc. in an efficient manner. Using a traditional 3D CFD tool for this type of analysis would create a huge model requiring excessive computing power to analyze.
On the other hand, if we limited our analysis to the straight onedimensional (1D) flow of the fuel through the piping, we would compromise accuracy by not considering the effects of the complex components in the system. A good solution is to analyze the many feet of piping using a 1D CFD analysis software, such as the Mentor GraphicFlowmaster1D flow simulation software, while inserting the models for the more complex components using 3D CFD analysis. Figure 5 shows an example of this type of system: an air-to-air refueling system with pipes and the refueling nozzle and how the combination of the 1D-3D analysis works.
The output from such an analysis could be a determination of the flow rates to refuel the jet or the “water hammer” effects if the aircraft were to suddenly disengage (Figure 6).
Example of Using CFD—Bell Helicopter Improves Safety, Saves Cost on Fuel Tank Design
Requirements
Bell Helicopter manufactures helicopters designed for a broad range of commercial and military applications. The latter class of aircraft includes defensive features designed to protect the helicopter and its occupants in the most adverse situations. Bell Helicopter needed a cost-effective evaluation solution that would give reliable results and guide the design of these and other complex features.
Bell engineers were tasked with reviewing and refining a system that injects nitrogen gas into the helicopter’s fuel tank to displace oxygen as the fuel is consumed. This makes the tank less likely to ignite if it is hit by an incendiary projectile. The incoming nitrogen must fill the tank’s recesses rapidly since, after all, the assumption is that the helicopter is under hostile fire and needs to escape as quickly as possible
เมื่อเราคิดว่า ของ CFD (คำนวณพลศาสตร์ของไหล) ในอุตสาหกรรมการบินและอวกาศ และการเดินอากาศ เรามักจะจำกัดความคิดของเราการวิเคราะห์อากาศพลศาสตร์ของโครงสร้างปีก/หางหรือ fuselages แต่ใช้ CFD วิเคราะห์ส่วนประกอบสำคัญเกือบทั้งหมดและระบบของเที่ยวบิน ตัวอย่าง ความร้อนมากเกินไปในชิ้นส่วนอิเล็กทรอนิกส์สามารถนำไปสู่ความล้มเหลวและความน่าเชื่อถือปัญหา ต้องปรับจัดส่งเชื้อเพลิงและระบบทำความเย็นของเครื่องยนต์ ระบบปรับอากาศ/เครื่องทำความร้อนห้องโดยสารจะวิเคราะห์ได้ และอุตสาหกรรมไม่สามารถ over-conservatively การออกแบบระบบเหล่านี้ (ต้นทุนมากเกินไป) หรือพิสูจน์ประสิทธิภาพ/ความน่าเชื่อถือ ด้วยการสร้างต้นแบบทางกายภาพหลาย การทดสอบในห้องแล็บ แล้ว ออกใหม่ ซึ่งเป็นกระบวนการยาวนาน และราคาแพง เนื่องจากปัญหาเหล่านี้ CFD มา เข้าเล่นก่อน และตลอด ทั้งกระบวนการออกแบบหลายคอมโพเนนต์และระบบในเครื่องบิน ไม่ relegated การใช้ CFD กับขอบเขตของผู้เชี่ยวชาญ ชั้นเรียนใหม่ของซอฟต์แวร์ CFD วิเคราะห์ "พร้อม CFD เป็นการพิสูจน์ให้มีประสิทธิภาพสูงในการวิเคราะห์เหล่านี้ การเปิดใช้งานออกแบบวิศวกรรวมทั้งผู้เชี่ยวชาญเร่งตัดสินใจที่สำคัญที่เวิร์กสเตชันของพวกเขา เป็นพวกเขาทดลองกับสถานการณ์การออกแบบ และพวกเขาเหลาในในการออกแบบที่ดีที่สุด มากที่สุดมีประสิทธิภาพ เชื่อถือได้ และคุ้มค่า ด้วย CFD ถูกฝังอยู่ในสิ่งแวดล้อมมิ กระบวนการนี้ใช้งานง่ายช่วยให้วิศวกรออกแบบเพื่อเพิ่มประสิทธิภาพของผลิตภัณฑ์ในระหว่างขั้นตอนการออกแบบ และต้นแบบทางกายภาพที่แรกมักจะเป็นการออกแบบไปเป็นผลิตขั้นสุดท้าย Until recently, the commercial software available for CFD typically has been geared toward only the specialists, limiting its widespread use. Besides being expensive, these tools have been challenging to use. As a result, engineering analysis for applications such as pressure drop, heat transfer, fluid flow, etc. traditionally have been carried out only by CFD specialists in analysis departments, separate from mainstream design and development departments. This limited the number of design approaches tested and taxed the overburdened specialists. Fortunately, new tools have emerged that embed a complete range of flow analyses within mainstream MCAD toolsets such as CATIA® V5, PTC Creo®, and Siemens NX™. For example, the FloEFD™ design/ analysis technology offered by Mentor Graphics is specifically targeted at the design engineer as well as the specialist. It has the combination of simulation accuracy plus the ease-of-use and speed needed to be used as an integral part of the design process. With these new CFD tools, a design engineer with standard training and working in any size company can use his or her existing knowledge to successfully perform analyses, all within the familiar MCAD environment of choice. Certainly, there will always be a few very demanding applications where more advanced CFD knowledge is needed to fine-tune the meshing and solver settings to converge to a solution. However, taking CFD out of the exclusive domain of specialists and bringing it into the mainstream enables design engineers with little specific training in CFD to analyze problems in roughly 80 to 90% of the time compared to using traditional tools. This offers designers a fundamental breakthrough in design efficiency. Characteristics of CFD Targeted at the Design Engineer For example, some CFD simulation software provides a complete environment for performing analysis such as heat transfer by combining all the phases of analysis in one single package: from solid modeling, to problem set up, running, results visualization, validating the design, and reporting. Figure 1 illustrates some of the important characteristics of CFD software that enables it to be useful to design engineers and not just specialists. MCAD system embedded All the designer needs is knowledge of the MCAD system and the physics of the product to use next-generation CFD. After installation, all the menus and commands necessary to run a full CFD flow analysis are created in the MCAD package’s menu system. This CFD embedded within the MCAD system makes it extremely easy to use. The design engineer is already familiar with the menu structures. The CFD analysis tool uses the same GUI structures so the engineer does not have to learn a completely new interface (Figure 2). The starting point of any heat transfer and fluid flow analysis is to define the overall boundary conditions of the problem. A wizard is available to direct the setup, including the selection of models. This lets a designer take advantage of existing MCAD models for analysis, without having to export or import additional data, saving significant amount of time and effort. The embedded CFD software can use newly created or existing 3D CAD geometry and solid model information to simulate designs in real-world conditions. Automated cartesian meshing Once a model is created, the model needs to be meshed. Developing a mesh is one of those skills that previously separated CFD specialists from mechanical design engineers. With FloEFD, meshes are created automatically in a matter of minutes rather than requiring hours of tedious proportioning of regions and cells. The software actually creates an adaptive mesh that reduces the cell size (increasing the resolution of the analysis) to ensure more accurate simulation results in complex areas of the model, as shown in Figure 3. Easy-to-Use engineer oriented interfaces Stepping through the analysis process can be very confusing to the non-specialist. However, with a next-generation CFD tool, the design engineer is stepped through the process by wizards that ensure all data such as materials, fluid characteristics, boundary conditions, and execution parameters are properly defined. Multi-Variant parametric modeling This feature enables the design engineer to set up a series of experiments and submit multiple analyses for batch runs. The engineer can define a range of values and then modify the design (number of fins on the heat sink, dimensions of an outlet, etc.) or boundary conditions (pressure, flow volume, temperature, etc.) across a spectrum. The software automatically generates a series of analysis runs and submits them for execution. The results of these experiments can be compared and visualized, and then the best design can be chosen. Laminar-Turbulent transitional modeling The modeling of a fluid flow is extremely complex while the flow transitions from laminar to turbulent or vice versa. In typical CFD software, this requires two different models and an understanding on the part of the engineer as to which one should be used. A model that senses this transition and automatically employs the correct modeling at the correct time in the transition eliminates the need for two different models and the intervention of the engineer (Figure 4). Automated/Guaranteed convergence One of the most difficult tasks even for the CFD specialist is to ensure that the CFD analysis converges. Many factors can contribute to a CFD analysis non-convergence. Model complexity, meshing, boundary conditions, etc. can all cause older-generation software not to converge. The specialist must then experiment, sometimes using trial and error, to urge the software into convergence. With software such as FloEFD, convergence is virtually guaranteed, thus eliminating the need for the design engineer to tweak the model. These are just some examples of the technologies that enable complex CFD to be put into the hands of the design engineer as well as the specialist. CFD Analysis from Complex Components to Systems When we think of CFD analysis, we might limit our thinking to the individual components of an aircraft or satellite, such as the electronics in a navigation computer for proper heat management, the fuel flow through an injector, or the capability of an oil cooling component. We might not imagine, given the size and complexity of a complete system such as fuel delivery, that we could analyze it with all the feet of piping, pumps, valves, etc. in an efficient manner. Using a traditional 3D CFD tool for this type of analysis would create a huge model requiring excessive computing power to analyze. On the other hand, if we limited our analysis to the straight onedimensional (1D) flow of the fuel through the piping, we would compromise accuracy by not considering the effects of the complex components in the system. A good solution is to analyze the many feet of piping using a 1D CFD analysis software, such as the Mentor GraphicFlowmaster1D flow simulation software, while inserting the models for the more complex components using 3D CFD analysis. Figure 5 shows an example of this type of system: an air-to-air refueling system with pipes and the refueling nozzle and how the combination of the 1D-3D analysis works. The output from such an analysis could be a determination of the flow rates to refuel the jet or the “water hammer” effects if the aircraft were to suddenly disengage (Figure 6). Example of Using CFD—Bell Helicopter Improves Safety, Saves Cost on Fuel Tank Design Requirements Bell Helicopter manufactures helicopters designed for a broad range of commercial and military applications. The latter class of aircraft includes defensive features designed to protect the helicopter and its occupants in the most adverse situations. Bell Helicopter needed a cost-effective evaluation solution that would give reliable results and guide the design of these and other complex features. Bell engineers were tasked with reviewing and refining a system that injects nitrogen gas into the helicopter’s fuel tank to displace oxygen as the fuel is consumed. This makes the tank less likely to ignite if it is hit by an incendiary projectile. The incoming nitrogen must fill the tank’s recesses rapidly since, after all, the assumption is that the helicopter is under hostile fire and needs to escape as quickly as possible
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