Numerical Simulations ∇ CFD Simulations
The numerical simulation is always used when flows are to be examined in detail without experimentation. However, the numerical simulation is not only characterized by the fact that the cost is significantly lower, but also by the fact that physical quantities are often not measurable. For example, it is not possible in an experiment to record the flow details in the entire measuring room, since the measuring instruments can often only determine local quantities. As already written on the main page of Holzmann CFD, numerical simulation can be used in a variety of engineering and science fields. Below are some examples to make numerical simulation easier to understand.
Fluid Flows and Hydraulic
Hydraulic problems or pipe flows of any kind can be examined numerically in order to better understand the flow behavior and to provide new technical solutions. The visual preparation of the results enables targeted approaches to be developed and implemented. Technically sophisticated solutions can also be checked numerically to ensure that the ideas that are implemented lead to the correct goal. As not every well-thought-out system takes into account all physical effects that exist, it is always helpful to analyze the design numerically.
Engineering approaches are often applied correctly, but various aspects are not taken into account. The result is, for example, geometrical internals that does not serve their intended purpose. This may reduce efficiency or, in individual cases, may even result in a system that has been incorrectly designed or not working optimally at the operating point.
Examples of this would be unexpected stalls, unnoticed inertia effects of the fluid (deflection of fluids), transient effects that were not known, and much more.
All fluid flows and hydraulic flow problems can be examined in a targeted and well-founded manner using numerical simulation.
Building and Ventilation Analysis
Numerical building and ventilation simulations, also known as Heat Ventilation and Air Condition (HVAC), are nowadays part of the state of the art analysis in building planning. Due to numerical simulations, the building ventilation can already be analyzed in the planning and concept phase, and measures for optimization can be taken already prior if necessary. Especially, the calculation of the flow and temperature field enables the determination of comfort indicators according to DIN ISO 7730, even before the construction phase began. These indicators provide information about the comfort of people inside buildings, halls, or other constructions such as theatres.
In general, HVAC analysis is not only used in the building sector. A numerical investigation of subway stations, entrance halls of shopping centers, or stadiums (of any kind) are also calculated, analyzed, and optimized in advance using numerical simulation.
HVAC analyzes are carried out even in the pharmaceutical industry. However, the term cleanroom or dustfree calculation is used here. In these scenarios, the CFD calculation often considers the distribution of particles in defined cleanrooms and workplaces.
Exhaust Gas Systems and Catalysts
Exhaust gas systems and catalysts are used in the automotive and plant engineering industries. The exhaust system differs in both industries only from the mass flow rates and possibly from the gas composition. However, the primary intensity in both sectors is the same: to maintain the maximum species conversion rate (limited exhaust emissions) with the lowest backpressure and at the same time to limit the noise emissions so that the standards and guidelines of the country are fulfilled.
While in the automotive sector, the intended use appears immediately (exhaust gas system), this is often not immediately obvious in plant engineering. However, the same intension is applied: reducing the species emissions (mainly NOx). For example, large gas or diesel engines are used in the energy sector to generate electricity and hot water (nowadays mainly gas engines). The burned natural gas-air mixture is released from the engine into the environment through large exhaust gas ducts. Similar to the automotive industry, high legal requirements regarding noise and pollutant emissions must be fulfilled. Therefore, silencer systems and catalytic converters are used here, of course, in a completely different size ratio.
Furthermore, silencer systems (absorption and resonator silencers) are analyzed concerning flow problems and improved if necessary. Heating curves of the catalysts can also be calculated numerically, using suitable models, or explosion calculations can be carried out. However, this is mainly of interest in plant engineering, for example, if the cylinder ignition systems fail, the natural gas / air mixture gets unburned into the exhaust gas duct and can be ignited there.
DeNOx Systems and Exhaust Gas Treatment
In the process engineering area, DeNOx systems and exhaust gas treatment regarding NOx emission limitation are analyzed using CFD analyses. Here, primarily the mixing of the reactant and exhaust gas is investigated in advance to ensure an ideal (homogeneous and well mixed) flow to the catalyst elements. While using numerical simulations, measures can be taken to improve the flow pattern. Furthermore, an optimization of the mixing of the DeNOx reactant and exhaust gas can be measured in order to achieve a homogeneous mixture of the flow streams in front of the catalytic converter. This saves catalyst volume and reactant consumption. Furthermore, it minimizes the ammonia slip.
In general, DeNOx and exhaust gas cleaning systems are used in plant construction for combustion and engine systems. DeNOx systems are also used in the automotive sector, explicitly for diesel-powered vehicles (keyword: diesel scandal).
The following internals are generally used to optimize the flow pattern inside the exhaust gas system:
- Static mixer
- Perforated plates
- Baffle plates (guiding plates)
The models used differ depending on the application. In general, Lagrangian models are used for particle injection and porosity models for modeling SCR and OXI catalysts zones. The injected DeNOx reactant (Lagrangian 's observation) is evaporated within the flue gas and is converted to ammonia (hydrolysis and pyrolysis), which is then converted to N2 with NO and NO2 on the SCR surface. Here, evaporation models can be used in combination with other assumptions.
Cooling and Heating Systems, Fans
Cooling and heating systems, as well as fan analyzes, can be calculated using numerical simulations. For example, water coolers for CPU units can be optimized by numerical simulations, and the flow field of the water can be analyzed. Dead flow and inadequate cooling zones can be determined through the simulations. The pressure loss of such a CPU cooler can also be calculated in order to select the correct water pump (power).
Cooling and heating systems can, therefore, be calculated individually and designed for the working point. Coupling with acoustic calculation libraries also enables the investigation of the noise generation of fan blades.
In the field of cooling and heating systems, the energy exchange of different regions is of primary interest. Energy exchange can be found in every technical device. For example, large heat exchangers are used in plant constructions to extract the energy from the exhaust gas and then make it available for other processes. The paper industry or the use of exhaust gas to heat districts are classic examples here. Heat exchangers are also used in other processes, for example, to cool circuits or to keep electronics or other technical equipment at a certain temperature level. Some cases are engine cooling applications, cooking plates, hairdryers, and much more.
Especially in the field of small components and in power electronics, the thermal energy exchange is often of significant interest. Here, CFD simulations are used to determine thermal stresses and keep the temperature gradient in a defined range and thus prevent thermal cracks (electronics).
Dynamic Systems and Flow-Induced Rotations
A supreme discipline in the numerical simulations are CFD analyzes of dynamic systems and fluid-induced rotations such as the motion of impellers or rotors of water turbines and wind turbines. The numerical simulation enables design optimizations, which increase the efficiency of the system or device.
The numerical models are used differently here. While the interaction between the fluid and solid is considered in flow-induced movements, a defined speed (angular velocities) is specified if, e.g., fans, centrifuges, or turbines are analyzed.
Dynamic systems are also used for engine analysis (piston movement) or other moving systems. If the appropriate assumptions and models for the dynamic system are set, rotary and translation motion can be evaluated, and an investigation into the fluid flow can be performed.
External fluid flows occur everywhere in nature and technical equipment. In the engineering sector, the drag and lift coefficients of a geometric shape are typical of particular interest. A classic example of this is the flow around a wing profile. The lift forces can be calculated using the numerical simulation.
External flows also occur in the automotive sector. Here, the drag force is commonly evaluated and minimized to reduce gasoline or diesel consumption.
Furthermore, external flows occur in the building sector. Numerical simulations can help to analyze possible vortex shedding at the building structure, which may lead to an increased load on the structure. The additional force may lead to a critical load state. Buildings such as bridges can be of particular interest here. The flow around the profiles may occur in the resonance frequency. The additional load can then lead to the failure of the statics (historical examples are already available here).
Classic examples are the flow calculation of entire geographic landscapes, cars, airplanes, and ships. The area of the building simulation (HVAC) can also integrated into the external flows.
Multiphase flows occur regularly in technical systems. Regardless of whether there are different immiscible liquids or different aggregate states of the fluid, these systems are referred to as multiphase systems.
The numerical simulation of multiphase flows can be used, for example, to examine river flows, and, for example, to generate a standing wave (see ice channel in Munich; keyword: hydraulic jump). The mixing of different fluids can also be examined in this way, especially when different CFD disciplines are brought together (dynamic systems - moving networks).
Strictly speaking, DeNOx systems in exhaust gas cleaning systems are also related to multiphase flows. Since a fine mist of liquid drops is introduced into the gas phase (exhaust gas carrier gas, carrier phase) (second phase). Instead of Lagrangian analyzes, Euler-Euler calculations (real multiphase flows) can also be performed here.
If the phase interface of two immiscible fluids can be clearly determined, the method called Volume-Of-Fluid (VOF) is often used. A wide variety of analyzes in the field of multiphase flows be analyzed in the process and chemical industries. Numerical simulations, including multiphase flow analysis with chemical reactions and dynamic meshes, are one of the most complex systems.
Are you interested in a numerical simulation to better understand physical effects, optimize your design, or use the data obtained for advertising purposes? Holzmann CFD reliably calculates your fluid flows in a variety of application areas, analyzes, and prepares the numerical data according to your individual requirements.
Through simulations, you gain insights that you can use to improve your design and thus act sustainably with the best performance in the market, while technology providing the best solution.
Numerical Stress Analysis
Numerical simulations can also be used in the field of stress analysis in solid bodies, for example, to calculate thermally-induced stresses. Of course, it is also possible to examine the stresses introduced due to fluid forces or due to contact with other rigid bodies.
Holzmann CFD analyzes your system and calculates the stresses occurring in the component. Especially in the area of the coupling of such problems, Dr. Tobias Holzmann has in-depth knowledge based on his doctoral thesis in the field of local heat treatment for cast aluminum alloys.