Get to Know Altair FlightStream

In May 2024, Altair acquired Research in Flight and with it the powerful CFD solver, FlightStream. Previously, Altair customers had access to Altair HyperWorks CFD Solvers like Altair Acusolve for general CFD applications (Also included in Altair SimLab), Altair Inspire Fluids, Altair nanoFluidX for free surface and sloshing simulations and Altair ultraFluidX for aerodynamics and aeroacoustics. In this post, we will look at the newly branded Altair FlightStream, what its capabilities are and what are some of its best applications.

What is Altair FlightStream?

Altair FlightStream is a rapid computational fluid dynamics (CFD) solver set designed specifically for the aerospace industry. It leverages advanced algorithms to provide accurate and efficient simulations of complex aerodynamic phenomena. It is a tool designed to provide quick and accurate solutions for complex flow conditions, including compressible and incompressible flows.

Fig 1: FlightStream screenshot stability control on a UAV

Key Features and Benefits

Streamlined Workflow for Rapid Results

FlightStream reduces computational requirements by focusing on the most critical aspects of the flow, such as the behavior near surfaces and in regions of high aerodynamic interest. This targeted approach reduces the number of calculations needed compared to solvers that attempt to model every aspect of the flow in detail. Key aspects include:

Surface Mesh Discretization

Unlike volumetric mesh methods that discretize the entire fluid domain (both around and inside the object), surface mesh discretization focuses only on the object's surface. This significantly reduces the number of elements and the computational load, making the simulations faster and more efficient.

Adaptive Meshing

The solver set employs adaptive meshing techniques that focus computational effort where it’s most needed, such as near leading edges, trailing edges, and areas with high gradients in flow properties. The ability to control mesh density ensures that computational resources are used efficiently, with finer meshes applied only where necessary. This balance between mesh resolution and computational cost is crucial for achieving accurate results within a reasonable timeframe.

Fig 2: Meshing example in FlightStream

Aeroacoustics Toolbox

A fully integrated aeroacoustics toolbox implemented under a NASA-funded STTR activity. This toolbox is capable of modeling both tonal and broadband noise components of UAM propellers, rotors and flexible structures. FlightStream exports all FAA vehicle certification acoustic data at the click of a button.

Aerodynamic Solvers

Altair FlightStream is designed to perform simulations of both steady and unsteady flows. This means that engineers can accurately model complex flow phenomena, such as turbulence, shock waves, and boundary layer effects, which are critical for understanding and optimizing the performance of aerospace vehicles. The variety of CFD solvers allows users to choose the right solver for their application. 

Panel Method and Vortex Lattice Method Solvers

The Panel Methods technique focuses on solving potential flow around the surfaces of interest, rather than throughout the entire flow field. This approach significantly reduces the number of calculations required compared to volume-based methods like finite element or finite volume solvers. As a result, simulations can be run much faster, enabling rapid design iterations and analyses.

The Vortex Lattice Method (VLM) solver is specifically designed to analyze the aerodynamics of lifting surfaces like wings and rotor blades. It models these surfaces using a lattice of bound vortices that simulate the lift distribution along the span and chord of the surface. This approach is particularly well-suited for analyzing the aerodynamic loads and performance of wings, control surfaces, and other components that generate lift.

Fig 3: Aerodynamic load example

Viscous Inviscid Solver (VII)

Combines an inviscid flow solver, such as a Panel Method or Vortex Lattice Method (VLM), with a boundary layer model to account for viscous effects. This approach provides a more accurate prediction of aerodynamic forces, including lift, drag, and pitching moments, than inviscid solvers alone. By considering both inviscid and viscous contributions to drag, the VII Solver can accurately predict total drag, including skin friction drag and pressure drag due to flow separation.

Fig 4: Viscous coupled with boundary layer example

Unsteady Aerodynamics Solver

Allows engineers to model time-varying flow conditions, such as gusts, maneuvers, and oscillatory motions. This capability is crucial for understanding how aerodynamic forces and moments change over time. This can be used to simulate transient events, such as sudden changes in angle of attack, rapid maneuvers, or the effects of wind gusts.

Fig 5: Rotorcraft example using Unsteady Solver

Compressible Flow Solver

Accurately captures the effects of compressibility, which are crucial when analyzing flows at high speeds. At supersonic, and hypersonic speeds, air behaves differently due to changes in density and pressure, and these effects must be considered to ensure accurate predictions of aerodynamic forces.

Fig 6: Left - Subsonic example in FlightStream, Right – F-18 Hornet at subsonic speed

Applications

While the primary applications for FlightStream have been in the aerospace industry, there are many applications that go far beyond that including maritime, turbomachinery and energy applications. Let’s look at these main industry applications in a little more detail.

Aerospace Industry

Allows engineers to optimize designs for better lift, less drag, and improved overall performance. By running these simulations, they can ensure that the aircraft is efficient, stable, and safe before it even takes flight. Because of its ability to focus on just the areas of importance, one strong example is the simulation of designs at subsonic and hypersonic speeds, where traditional CFD methods take an extended period of time and are very hardware intensive.  The solver set is ideal for working on aerospace applications.

Maritime Industry

Users can analyze the performance of ships and underwater vehicles using the Viscous Inviscid Solver (VII). These simulations commonly include focus on boundary layers and flow separation, which is ideal for this solver. It simulates how water flows around the hull, propellers, and other parts of the vessel, helping engineers reduce resistance and improve fuel efficiency. This is particularly important for designing ships that move smoothly through water and consume less energy. Also, the surface mesh discretization enables users to analyze water flow around ship hulls, optimizing the design to reduce drag and improve fuel efficiency.

Turbomachinery Industry

In the turbomachinery industry, which includes things like jet engines, turbines, and compressors, FlightStream can be used to study how air or other fluids flow through these machines. One of the main goals in turbomachinery design is to maximize the efficiency of energy conversion. Whether in a jet engine (where fuel energy is converted into thrust) or a gas turbine (where fuel energy is converted into electricity), FlightStream allows users to understand this process better to enable them to optimize the aerodynamic design to achieve higher efficiency.

Wind Energy Industry

Similar to the turbomachinery industry, FlightStream can be used to improve the design of wind turbine blades. The aerodynamic performance of wind turbine blades is critical to the efficiency of the entire turbine. FlightStream allows engineers to simulate the airflow over the blades, optimizing the shape and structure to maximize lift and minimize drag. This ensures that the blades capture as much wind energy as possible, converting it into rotational motion efficiently.

Altair FlightStream is a versatile tool that helps engineers in different industries simulate and optimize the flow of air and water around vehicles and machines. Whether it’s making airplanes more efficient, ships faster, engines more powerful, or wind turbines more productive, FlightStream provides the insights needed to design better and more efficient systems. We are excited to see FlightStream become available for Altair customers shortly.  If you have any questions or want to explore FlightStream further, reach out to us.