Exciting advances in Wind Engineering using ANSYS CFD
Wind engineering requires engineers to consider how a building responds to its environment as well as the effect that the structure will have on the space around it. Learn more about the use of CFD in wind engineering...
Using CFD to predict flow-generated noise and other aeroacoustic effects
Flow-generated noise can have significantly adverse effects on our everyday lives. Product designers and engineers at the world’s most innovative and successful companies have recognised this fact, and are increasingly using CFD to incorporate noise mitigation strategies into their product design process.
Can CFD help to solve Australia’s greatest aviation mystery?
On a stormy night in August 1981, a Cessna Centurion 210 aircraft crashed with 5 people on board in Barrington Tops, a rugged and isolated national park north of Newcastle, New South Wales. Despite a massive initial search effort and ongoing attempts by a group of dedicated volunteers, the challenging and complex terrain has conspired to prevent the wreckage from ever being found. To put this into some perspective: according to Corporal Mark Nolan (Pilot, Australian Army), this is the only aircraft to have crashed on mainland Australia and never be recovered. We can only imagine how frustrating and heartbreaking this must be for the victim’s families to be denied this closure. One of the biggest factors that has inhibited previous search attempts is the rugged, dense bushland in the Barrington Tops national park. NSW Police Superintendent Peter Thurtell confirms that “the terrain out there is as rugged as anywhere you'll find in Australia.” Importantly, he notes that the primary search area has two steep ridges that makes it particularly difficult to get in and out each time, furthering hampering the efficiency of any search efforts. However, with recent advances in technology and some novel use of computational fluid dynamics using ANSYS ICEM and ANSYS CFD, we hope that this mystery is about to be cracked wide open. This coming weekend, the concerted efforts of numerous professional and volunteer organisations (including Police Rescue, National Parks and Wildlife, NSW Rural Fire Service, NSW State Emergency Service and the Bushwalkers Wilderness Rescue Squad) will combine to have over 100 members on the ground searching for the elusive wreckage of Cessna 210M VH-MDX. Police Superintendent Peter Thurtell adds that while the team is not overly confident, a lot of planning has been done and he now believes "we've identified an area that gives us the best chance of locating the plane." At this point, you may ask how CFD has contributed to solving this 32 year-old mystery? In advance of this major search operation in October 2013, the search coordinators recently undertook a major push to evaluate all the available evidence and comprehensively review all of the theories about what happened to the aircraft. The technology involved includes side-scan sonar of the Chichester Dam, high-resolution aerial photography as well as LIDAR scans of the likely crash site. After painstaking evaluation of the available evidence, the likely crash site was narrowed down significantly by a team of 5 people, including a Police Rescue intelligence officer, a Police GIS officer, a Navy Pilot, a 1981 Air traffic control operator and a dedicated volunteer, Glenn Horrocks, who just happens to be a specialist CFD engineer (in his ‘day...
Turbulence Part 5 - Overview of Scale-Resolving Simulations (SRS)
An increasing number of industrial CFD users are recognising the need to move away from RANS modelling and resolve a greater spectrum of turbulence (particularly in cases involving large-scale separation, strongly swirling flows, acoustics, etc.). Here we present an overview of Scale Resolving Simulation techniques and important considerations when considering applying SRS to your project.
Tips & Tricks: Estimating the First Cell Height for correct Y+
In previous posts we have stressed the importance of using an appropriate value in combination with a given turbulence modelling approach. Today we will help you calculate the correct first cell height () based on your desired value. This is an important first step as the global mesh resolution parameters will also be influenced by this near-wall mesh as well as the Reynolds number. Let's review the two main choices we have in choosing a near-wall modelling strategy: Resolving the Viscous Sublayer Involves the full resolution of the boundary layer and is required where wall-bounded effects are of high priority (adverse pressure gradients, aerodynamic drag, pressure drop, heat transfer, etc.) Wall adjacent grid height must be order Must use an appropriate low-Re number turbulence model (i.e. Shear Stress Transport) Adopting a Wall Function Grid Involves modelling the boundary layer using a log-law wall function. This approach is suitable for cases where wall-bounded effects are secondary, or the flow undergoes geometry-induced separation (such as many bluff bodies and in modern automotive vehicle design). Wall adjacent grid height should ideally reside in the log-law region where All turbulence models are applicable (e.g. Shear Stress Transport or k-epsilon with scalable wall functions) During the pre-processing stage, we need to estimate the first cell height ( ) so that our falls within the desired range. The computed flow-field will dictate the actual value which in reality will vary along the wall. In some cases, we may need to locally refine our mesh to achieve the desired value in all regions. So how to calculate the First Cell Height for a desired Y+ value? Firstly, we should calculate the Reynolds number for our model based on the characteristic scales of our geometry such that: , where and are the fluid density and viscosity respectively, is the freestream velocity, and is the characteristic length (e.g. pipe diameter, body length, etc.). The definition of the value is such that: The target value and fluid properties are known a priori, so we need to calculate the frictional velocity , which is defined as: The wall shear stress, can be calculated from skin friction coefficient, , such that: The ambiguity in calculating surrounds the value for . Empirical results have been used to provide an estimate to this value: Flow Type Empirical Estimate Internal Flows External Flows We can then input these known values into the above equations to estimate our value for . When considering simple flows and simple geometry, we might find this correlation is highly accurate. However, when considering complex geometry, refinement in the boundary layer may be required to ensure the desired value is achieved. In these cases, you can choose to re-mesh in ANSYS Meshing or use anisotropic mesh adaption (ie. adaption of local cells only in...
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