On the quantification and visualization of transient periodic instabilities in pulsatile flows

Area of Science:

• Cardiovascular fluid dynamics
• Biomechanical engineering
• Computational fluid dynamics

Background:

• Cardiovascular flow studies increasingly report turbulent-like flows without cycle-to-cycle variations.
• Quantifying the mechanobiological relevance of these flows is challenging due to limitations of classical methods like Reynolds decomposition.

Purpose of the Study:

• To introduce novel frequency-based operators for objective quantification of transient, cycle-invariant turbulent-like flows in cardiovascular systems.
• To differentiate flow instabilities from underlying cardiac pulsatility.

Main Methods:

• Decomposition of flow signals into low- and high-frequency components using a high-pass filter (25Hz cut-off).
• Introduction of the spectral power index and computation of fluctuating kinetic energy based on filtered velocity components.
• Evaluation in an aneurysm model using computational fluid dynamics simulations at various flow rates.

Main Results:

• Frequency-based operators demonstrated a stronger correlation with qualitatively observed flow instabilities than conventional descriptors (e.g., time-averaged wall shear stress, oscillatory shear index).
• The proposed methods successfully isolated high-frequency components indicative of turbulent-like flow characteristics.
• Demonstrated analysis and visualization of high-frequency flow data.

Conclusions:

• The developed frequency-based operators provide a robust method for separating and quantifying cycle-invariant turbulent-like flows in cardiovascular applications.
• These operators offer improved objectivity and correlation with flow instabilities compared to traditional metrics.
• The methodology is generalizable and extendable to other cardiovascular regions.