What is it about?
This study explains how aircraft flying close to the ground can experience sudden choking of airflow beneath them, triggered by a narrowing between the aircraft and the ground. This phenomenon, predicted by the Sanal flow choking model, causes shock wave formation and performance loss—especially in low-flying, high-speed vehicles. Sanal flow choking is a localized fluid flow effect that satisfies all conservation laws and is free from assumptions or approximations. It occurs precisely at a critical pressure ratio, regardless of how that ratio is achieved. This model is a scientific breakthrough with broad impact: it not only improves the understanding of ground-effect aerodynamics but also helps predict deflagration to detonation transitions, asymptomatic strokes, and myocardial infarction. It provides a universal benchmark for CFD code verification and guides the design of chemical rockets, transonic aircraft, ground-effect vehicles, and drug development for heart disease.
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Why is it important?
Sanal flow choking is a universal fluid dynamic phenomenon that occurs in internal or external flow systems at a critical pressure ratio, regardless of the viscosity, geometry, or energy input method. It leads to shock wave formation, acoustic amplification, and potentially catastrophic failure in systems with blockage, divergence, or bifurcation regions. What makes this work unique is the application of the Sanal flow choking model to ground-effect aerodynamics—a critical but underexplored area in aerospace safety. This study provides the first proof-of-concept demonstration of external flow choking in low-flying aircraft, revealing how shock waves and lift loss can occur due to boundary-layer buildup near the ground. The findings enable precise CFD code validation and support safer design of aircraft, drones, and reentry vehicles operating in near-ground conditions. The same model also has broader implications for detonation prediction, stroke and MI risk assessment, and drug design—making this discovery both timely and transformative.
Perspectives
The Sanal flow choking model, which I had the privilege to develop with an international team, represents a scientific breakthrough with global relevance. Originally conceived to explain flow choking in aerospace systems, this model has evolved into a powerful framework for understanding diverse phenomena—from detonation in chemical rockets to asymptomatic strokes and myocardial infarction in humans. In our investigations, we comprehended that when blood pressure falls below the vapor pressure, microbubbles nucleate within the cardiovascular system. This microbubble formation increases the compressibility of blood, a factor traditionally overlooked in hemodynamics. These findings highlight the compressible nature of blood and its central role in decompression-related pathologies. As sound waves propagate through this bubbly medium, oscillating microbubbles absorb energy and alter wave behavior. The wave speed can reduce drastically—approaching blood flow velocity—leading to multiphase Sanal flow choking in the cardiovascular system. This mechanism provides a novel explanation for flow instabilities and shock-like events under decompression, such as those experienced by astronauts, divers, or high-altitude aviators. Beyond biomedical implications, the model remains a robust benchmark for CFD code verification and design of transonic aircraft, ground-effect vehicles, and valves in pipelines prone to cavitation. Notably, we’ve discovered that Sanal flow choking can be mitigated by increasing the heat capacity ratio of the working fluid or decreasing the total-to-static pressure ratio. I am hopeful that this interdisciplinary model will drive innovations in both engineering design and clinical strategy, uniting the fields of aerospace and medicine in addressing life-critical challenges.
Dr. SANAL KUMAR VR
Amity University
Read the Original
This page is a summary of: The theoretical prediction of the boundary-layer-blockage and external flow choking at moving aircraft in ground effects, Physics of Fluids, March 2021, American Institute of Physics,
DOI: 10.1063/5.0040440.
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