Car Demonstration Also See Acoustics Demonstration

LINFLOW (developed by ANKER–ZEMER Engineering AB in Karlskoga, Sweden) is a Fluid/Structure Interaction (FSI) software package that bridges the gap between Computational Fluid Dynamics (CFD) and structural dynamics, enabling engineers to visualize and understand the dynamics of fully coupled fluid/structure systems. LINFLOW complements Navier-Stokes based fluid dynamic solutions and FE based structure dynamics. LINFLOW makes it possible to study the response of aero- and hydro-elastic systems in a reasonable time. LINFLOW reduces computer time by orders of magnitude compared to other methods and results compare extremely well to measurements. LINFLOW uses the Boundary Element Method for the discretization of the velocity potential. Because of the general and rigorous mathematics and numerical methods employed by LINFLOW, users can study internal and external acoustics accounting for steady flow effects (acoustics in flowing media).

LINFLOW analyzes Fluid Flow, Aeroelasticity, Acoustics, Fluid-Structure Interaction, and Aeroelastic Stability (flutter prediction). It is excellent for studying propellers, fans, vibrations in ducts and pipes, lift and drag of airfoils and spoilers, acoustics, and general FSI. Recent additions to LINFLOW include a spectrum analysis (PSD) module, an enhanced p-k-stability analysis module, a (semi-) automatic wake element generation tool, and improved numerical procedures.

Methods used by LINFLOW differ greatly from other FSI products. Many other software packages simulate FSI by directly coupling Navier-Stokes solvers, for general fluid flow, with finite element analysis software, for statics and structural dynamics. The concept of directly coupling CFD and structural analysis is very general and works well for certain classes of problems. Direct coupling allows for the inclusion of structural nonlinear effects in the problem. However, direct coupling is not very well suited for vibration problems (acoustics, aeroelasic stability analysis to predict flutter, etc.). Even for small, single point, low frequency problems, the approach is computationally very inefficient. For higher frequency problems (fans, flow induced vibrations in pipes, etc.) direct coupling between a Navier-Stokes solver and a structural analysis program is practically unfeasible due to the computer resources needed.

In contrast, LINFLOW solves small amplitude, high frequency FSI problems several orders of magnitude faster than software based on other concepts.

LINFLOW can be used to study fluid flow, provided the fluid can be considered inviscid and irrotational. Thus, there are many FSI problems where a Navier-Stokes solver is needed to capture fluctuations due to viscous effects. The calculated spectrum of the unsteady pressure oscillations is then input to LINFLOW for fluid-elastic response analysis. See Aeroelastic Analysis of Fan System Dynamics by Jari Hyvärinen (PDF format) for an example of this method.

LINFLOW may be used alone or in combination with other software such as:

• Structural: Structural analysis system to compute Eigenvalues, Eigenforms, and Modal Load Vector for LINFLOW and for stress and displacement calculations.
• Navier-Stokes Solver (NSS): CFD software for general fluid flow.
• Large Eddy Simulation (LES): CFD Software for detailed simulation of fluid flow, allowing large scale turbulent eddies to be calculated explicitly and small scale turbulent eddies calculated with a sub-grid model.

Typical combinations include:

LINFLOW

Steady and unsteady irrotational and inviscid fluid flow.

Structural	LINFLOW
FSI analysis for eigenfrequencies of combined fluid/structure system, for static or dynamic fluid. Aeroelastic stability analysis, p-k or v-g, compressible or incompressible.

Structural	LINFLOW	Structural
FSI based structural response (harmonic and response spectrum) for displacements and stresses, acoustics.

NSS	Structural	LINFLOW	Structural
Finds pulsations in the pressure field for input to LINFLOW.

NSS/LES	LES	Structural	LINFLOW	Structural
Checks for instationary fluid flow behavior (LES for more resolution).	Finds fluctuations in the pressure field for input to LINFLOW.