In the realm of fluid dynamics, certain phenomena captivate both scientists and enthusiasts alike. One such captivating occurrence is the formation of shock diamonds, also known as mach diamonds or mach disks.
These striking patterns emerge when jet exhaust travels faster than the speed of sound in the atmosphere. Recently, a viral video demonstrated an unexpected source of these mesmerizing patterns: a humble soda bottle filled with water and pressurized with air.
How Can a Soda Bottle Create Shock Diamonds?
The viral video showcased a simple yet remarkable experiment: a plastic soda bottle partially filled with water and sealed tightly. When air pressure was introduced into the bottle, the water was expelled through a small nozzle at supersonic speeds. The result? A series of brilliant shock diamonds illuminated against the dark backdrop. But how does this seemingly mundane setup produce such an awe-inspiring display?
Shock Diamonds: A Brief Overview
Shock diamonds emerge due to supersonic flow and compression waves. As air rushes through a nozzle or exhaust pipe, it accelerates to supersonic velocities. The abrupt expansion of high-pressure gas into lower-pressure surroundings generates compression waves, creating regions of alternating high and low pressure. These pressure variations lead to the formation of shock diamonds.
The role of the Mach number is crucial in this phenomenon. When the Mach number exceeds 1 (indicating supersonic flow), shock waves form. Each shock wave corresponds to a shock diamond. These diamonds exhibit repeating patterns due to constructive and destructive interference between compression waves. The alternating regions of high and low pressure cause light to refract differently, resulting in visible bands.
Shock diamonds possess aesthetic allure due to their symmetry and luminosity. The intense pressure gradients create localized heating, causing gases to emit light—a process known as chemiluminescence. The resulting glow accentuates the diamond-like shapes, captivating observers whether witnessed in rocket plumes or captured in viral videos.
Take a look at a soda bottle creating these beautiful diamonds.
A soda bottle filled with water and pressurized with air creates supersonic exhaust and shock diamonds. Also called mach diamonds or mach disks, they occur when jet exhaust travels faster than the speed of sound in atmosphere and tend to exhibit repeating 
Real-World Applications of Shock Diamonds
Shock diamonds are more than just beautiful to look at, they play an important role in real world situations. For example in Aerospace Engineering, jet engines, rocket nozzles, and afterburners often display shock diamonds. Engineers sometimes use the shock diamond output as a threshold to optimize nozzle designs to enhance thrust efficiency while minimizing noise.
In combustion research, studying shock diamonds aids in understanding combustion processes. Researchers investigate flame stability and pollutant emissions.
The soda bottle shock diamond experiment serves as a delightful reminder that scientific wonders can emerge from everyday objects. Whether witnessed in rocket plumes or captured in viral videos, shock diamonds continue to inspire curiosity and awe.
As we gaze at these luminous patterns, we glimpse the intricate dance between fluid dynamics and aesthetics—a dance that transcends disciplinary boundaries, and invites us all to marvel at the beauty hidden within our world.