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The Power of Hypersonic Wind Tunnels: Testing Grounds for Future Hypersonic platforms and Technologies

Introduction:

In the world of advanced military and technological development, the race to achieve hypersonic speeds has become increasingly competitive. Hypersonic vehicles, capable of traveling at speeds exceeding Mach 5 (approximately 3,800 miles per hour), offer a new paradigm in military capabilities and technological advancements. At the heart of this race lies a critical infrastructure: hypersonic wind tunnels. These testing grounds serve as the backbone for the development and evaluation of future hypersonic platforms and technologies, playing a pivotal role in geopolitical military and technological landscapes.

 

The era of hypersonic flight had arrived.

Hypersonic refers to aircraft, missiles, rockets, and spacecraft that can reach speeds through the atmosphere faster than Mach 5, which is near 4,000 miles per hour. The hypersonic wind tunnel is used to test flight characteristics in a hypersonic region of Mach number 5 or more.

Aerospace engineer Steven Beresh emphasizes the immense difficulty of the physics involved in hypersonic speed. Air and gases behave differently compared to subsonic speed, materials experience extreme temperatures and pressure, and guidance mechanisms must withstand these challenging conditions.

The hypersonic regime introduces a multitude of complex flow attributes, including high turbulence, pressure, temperature, density, vorticity, and energy. Other factors such as thin shock layers, viscous interactions, entropy layers, changes in vehicle stability and control, and physical-chemical gas changes like ionization, dissociation, and equilibrium effects further complicate the understanding of hypersonic aerodynamics.

The current knowledge base in this field is limited, especially considering the shift from focusing solely on vehicle survival during re-entry to ensuring the vehicle thrives throughout the entire hypersonic flight. Researchers are actively striving to overcome these challenges to successfully navigate through hypersonic environments.

Hypersonic research has revealed several persistent challenges in vehicle aerodynamics, primarily due to the limitations of ground testing facilities for simulating hypersonic flows. One key challenge is the scarcity of an extensive aerothermodynamic flight test database. Access to existing databases is often restricted, and there have been limited efforts to verify computational fluid dynamics (CFD) aerothermodynamic codes against ground test data.

What are Hypersonic wind tunnels?

Hypersonic wind tunnels are specialized testing facilities designed to simulate and study the aerodynamic characteristics of hypersonic flight. These tunnels play a crucial role in the development and evaluation of hypersonic platforms and technologies.

The primary objective of a hypersonic wind tunnel is to generate a hypersonic flow field in the working section, replicating the typical flow features and conditions experienced during hypersonic flight. This includes factors such as compression shocks, pronounced boundary layer effects, entropy layers, viscous interaction zones, and high total temperatures of the flow. By creating an environment that closely mimics hypersonic flight, researchers can gather valuable data and insights to refine the design and performance of hypersonic vehicles.

Hypersonic wind tunnels are equipped with advanced instrumentation and measurement systems to capture various parameters during testing. These include pressure sensors, temperature sensors, force and moment sensors, and flow visualization techniques. The collected data provides researchers with a comprehensive understanding of the aerodynamics, thermal management, structural integrity, and propulsion characteristics of hypersonic vehicles.

There are different types of hypersonic wind tunnels, each offering specific capabilities and operating principles. One common type is the shock tunnel, which uses a combination of high-pressure gas storage and rapid release to create the hypersonic flow. Another type is the expansion tube, which utilizes the expansion of high-pressure gas into a low-pressure environment to generate hypersonic speeds.

These wind tunnels are typically large, complex structures that require precise engineering and control systems. They employ high-temperature and high-pressure gases, often including a mix of air and combustion products, to achieve the desired flow conditions. Safety measures are in place to handle the extreme conditions within the tunnels, ensuring the protection of personnel and equipment.

Hypersonic wind tunnel testing poses numerous challenges due to the unique nature of hypersonic flows. Matching the aerodynamic conditions accurately, maintaining cost-effectiveness, and achieving rapid turnaround times are among the key difficulties faced by researchers.In addition to creating databases, analyzing the fundamental fluid dynamics of hypersonic flow, such as boundary layer transition and its effects on surface heating, is essential for aerodynamic research. This comprehensive understanding contributes to the development of advanced hypersonic vehicles and technologies. However, despite these challenges, hypersonic wind tunnels remain indispensable tools for advancing hypersonic flight technology.

To make substantial progress in hypersonic research, collaboration among experts from different disciplines is crucial. This includes individuals knowledgeable about hypersonic vehicles, fluid dynamics, measurement science, and computer simulations. By pooling their expertise, researchers can gain a deeper understanding of the underlying physical phenomena and make significant advancements in hypersonic technology.

The advances in Computational fluid Dynamics ( CFD) modelling on high speed supercomputers has reduced the demand of wind tunnel testing but the modelling results are still not completely reliable and wind tunnels are used to verify CFD predictions.

In summary, hypersonic wind tunnels are specialized facilities that enable researchers to simulate and study the complex aerodynamic characteristics of hypersonic flight. Through their capabilities and instrumentation, these testing grounds contribute significantly to the understanding and development of hypersonic platforms and technologies, playing a vital role in shaping the future of high-speed aerospace endeavors.

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Geopolitical Significance:

Geopolitically, hypersonic technology has gained immense attention due to its potential to reshape the balance of power. Nations with advanced hypersonic capabilities can gain significant military advantages, including enhanced strike capabilities, rapid response times, and the ability to penetrate existing defenses. Hypersonic platforms can overcome traditional missile defense systems, making them a potent force multiplier for nations that possess them. As a result, countries worldwide are investing heavily in hypersonic research and development programs to secure their positions in the new era of military dominance.

Military Implications:

Hypersonic wind tunnels are indispensable in evaluating and refining the performance of hypersonic platforms. These facilities enable researchers and engineers to simulate hypersonic flight conditions, allowing them to understand aerodynamic forces, thermal management, and structural integrity. By subjecting prototypes to extreme conditions, researchers can optimize their designs, enhance maneuverability, and ensure operational viability.

Moreover, hypersonic wind tunnels contribute to the development of advanced hypersonic propulsion systems. These tunnels facilitate the study of airflow and the combustion processes that occur within hypersonic engines. By analyzing and fine-tuning engine performance, researchers can achieve greater efficiency, reliability, and power, paving the way for more advanced hypersonic vehicles.

 

 

US Infrastructure

According to a study conducted by the Institute for Defense Analyses (IDA) in 2014, the United States had 48 critical hypersonic test facilities and mobile assets essential for the development of hypersonic technologies. These facilities included DOD ground test facilities, open-air ranges, mobile assets, NASA facilities, Department of Energy facilities, and industry/academic facilities.

However, the study also highlighted that no existing U.S. facility could provide the necessary full-scale, time-dependent, coupled aerodynamic and thermal-loading environments for evaluating characteristics above Mach 8. Since then, progress has been made with the opening of a Mach 6 hypersonic wind tunnel at the University of Notre Dame and ongoing development of Mach 8 and Mach 10 wind tunnels at Purdue University and the University of Notre Dame, respectively.

The United States also utilizes international test ranges, such as the Royal Australian Air Force Woomera Test Range in Australia and the Andøya Rocket Range in Norway, for flight testing. In addition, the Navy plans to reactivate its Launch Test Complex at China Lake, CA, to enhance air launch and underwater testing capabilities.

One notable facility is the Naval Research Laboratory (NRL) Hypersonic Wind Tunnel, which offers a long-duration mid-size aerodynamics test capability with the ability to vary altitude and speed in real-time. The range spans sea level to over 30km and Mach 1.3 to 6+ in a 12” x 12” x 24” test section. Pressurized air is stored in stagnation tanks, then forced through a convergent-divergent planar nozzle where it reaches a sonic condition at the throat. The flow then expands to supersonic speeds in the test section at the desired density altitude or turbulence level and Mach number. This wind tunnel can simulate a wide range of flight conditions, including varying Mach numbers, Reynold’s numbers, density altitude, and dynamic pressure. It provides cost-effective operation and rapid test turnaround, with air tanks being recharged in less than 90 minutes.

In summary, the United States possesses a significant number of hypersonic test facilities and mobile assets, but challenges remain in providing comprehensive evaluation capabilities for hypersonic technologies. Ongoing efforts include the development of advanced wind tunnels and the utilization of international test ranges to support hypersonic research and development.

U.S. Army Hypersonic Test Center

The U.S. Army Hypersonic Test Center, located at the RELLIS campus in Texas, is set to become a hub for collaboration and advanced testing in support of national security. The Texas A&M Engineering Experiment Station has secured a $65 million cooperative research agreement with the Combat Capabilities Development Command (CCDC)-Army Research Laboratory (ARL), and an additional $50 million has been allocated by the Texas State Legislature for Army Futures Command efforts.

The center aims to assist the U.S. Army Futures Command in its modernization mission by enabling soldiers from Fort Hood and the A&M Corps of Cadets to test high-tech prototypes during their development. With a budget of $200 million, the facility will house cutting-edge laboratories, runways, underground and open-air ranges, as well as a resilient network of sensors and systems for experimentation, data collection, analysis, and storage.

Of particular significance, the center will feature the nation’s only kilometer-long hypersonic facility, allowing researchers to evaluate the most effective designs and materials for the fastest vehicles ever built. The establishment of this state-of-the-art complex is expected to attract private investments, making Central Texas a desirable location for defense contractors collaborating with the U.S. Army Futures Command.

In summary, the U.S. Army Hypersonic Test Center at the RELLIS campus will enhance collaboration, testing capabilities, and accelerate the procurement process for the U.S. Army. It will provide critical infrastructure for the development and evaluation of high-tech prototypes, including a unique kilometer-long hypersonic facility, positioning Texas as a prominent hub for advanced defense research and development.

Engineers make modifications at Arnold AFB hypersonic propulsion unit

Engineers at Arnold Air Force Base (AFB) have successfully addressed issues with an electrical component in the Aerodynamics and Propulsion Test Unit (APTU), a blowdown wind tunnel used for aerodynamic testing of supersonic and hypersonic systems. The team made software modifications to detect unsafe conditions, prevent damages, and avoid unnecessary downtime. By enhancing the programmable logic controllers, electrical engineer Adam Webb was able to handle uncommanded runaways of the rectifier, preventing unplanned test terminations, fuel system damage, and unscheduled test repeats.

Additionally, instrumentation data and controls engineer Gareth Penfold developed a computer database to track equipment calibration, spare instruments, and warranty dates. This new system improves the efficiency of instrument management and provides time-sensitive data for engineering decision-making.

The APTU facility at Arnold AFB is capable of generating test conditions ranging from Mach 3.1 to Mach 7.2, allowing for a wide range of tests related to propulsion, materials, structures, store separation, and directed energy lethality/survivability. The successful modifications and database implementation ensure the continued reliability and effectiveness of the APTU facility in supporting crucial aerodynamic testing of high-speed systems.

Russian Infrastructure

Russia reportedly conducts hypersonic wind tunnel testing at the Central Aero-Hydrodynamic Institute in Zhukovsky and the Khristianovich Institute of Theoretical and Applied Mechanics in Novosibirsk, and has tested hypersonic weapons at Dombarovskiy Air Base, the Baykonur Cosmodrome, and the Kura Range.

Central Aerohydrodynamic Institute (TsAGI) in Zhukovsky, Moscow Oblast.

TsAGI is one of the oldest and largest aeronautics research centers in the world. It has a number of hypersonic wind tunnels, including the largest in Russia, the T-101. The T-101 can simulate speeds up to Mach 25.

Institute for Problems in Mechanics of the Russian Academy of Sciences (IPMech RAS) in Moscow.

IPMech RAS has a number of hypersonic wind tunnels, including the G-3. The G-3 can simulate speeds up to Mach 20.

Khrunichev State Research and Production Space Center in Moscow.

Khrunichev is a major manufacturer of space launch vehicles and spacecraft. It has a number of hypersonic wind tunnels, including the M-2. The M-2 can simulate speeds up to Mach 18.

These facilities are used to test a variety of hypersonic vehicles, including scramjets, hypersonic glide vehicles, and hypersonic missiles. The data from these tests is used to improve the design and performance of these vehicles.

In addition to these government-funded facilities, there are also a number of private companies in Russia that are developing hypersonic wind tunnels. These companies are developing the technology to meet the growing demand for hypersonic vehicles from the Russian military and commercial sectors.

 

Chinese Infrastructure

China has a robust research and development infrastructure devoted to hypersonic weapons. USD (R&E) Michael Griffin stated in March 2018 that China has conducted 20 times as many hypersonic tests as the United States.  China tested three hypersonic vehicle models (D18-1S, D18-2S, and D18-3S) each with different aerodynamic properties in September 2018.  Analysts believe that these tests could be designed to help China develop weapons that fly at variable speeds, including hypersonic speeds. Similarly, China has used the Lingyun Mach 6+ high-speed engine, or “scramjet,” test bed  to research thermal resistant components and hypersonic cruise missile technologies.

Lingyun-1 Hypersonic Cruise Missile Prototype

 

Chinese constructing world’s most high speed Hypersonic Win Tunnel

The wind tunnel, which is being built by the Chinese Academy of Sciences (CAS) at its Institute of Mechanics in Beijing, is scheduled to be completed in 2023. It will be the largest and fastest hypersonic wind tunnel in the world, capable of simulating speeds up to Mach 30.

The wind tunnel is being built to support China’s growing research and development efforts in hypersonic weapons and vehicles. Hypersonic weapons are capable of traveling at speeds of Mach 5 or greater, which makes them difficult to track and intercept. China has already conducted a number of successful tests of hypersonic weapons, and the new wind tunnel will help it to further develop and improve these weapons.

The wind tunnel is also being used to support China’s efforts to develop hypersonic commercial aircraft. Hypersonic aircraft could travel at speeds of Mach 5 or greater, which would make them much faster than traditional aircraft. This could potentially revolutionize the travel industry, as it would allow people to travel between distant cities in a fraction of the time it currently takes.

The construction of the wind tunnel is a significant step forward for China’s hypersonic weapons and vehicles programs. It will allow China to conduct more realistic and accurate tests of these weapons, which will help it to improve their performance and reliability. The wind tunnel is also a sign of China’s growing ambition in the hypersonic weapons and vehicles field. China is clearly determined to become a leader in this field, and the new wind tunnel will help it to achieve that goal.

Here are some additional details about the wind tunnel:

  • It will be 265 meters long and 10 meters in diameter.
  • It will be capable of generating air flow speeds up to Mach 30.
  • It will be used to test a variety of hypersonic weapons and vehicles, including scramjets, hypersonic glide vehicles, and hypersonic missiles.
  • The wind tunnel is being built at a cost of $1 billion.

The completion of the wind tunnel is a significant achievement for China. It is a sign of China’s growing ambition in the hypersonic weapons and vehicles field, and it will help China to become a leader in this field.

A new hypervelocity wind tunnel in China has passed its acceptance check.

China has successfully completed the development of a world-leading hypervelocity wind tunnel, the JF-22, which is expected to play a crucial role in the country’s advancement in aerospace transport systems and hypersonic aircraft. The project, sponsored by the National Natural Science Foundation of China and undertaken by the Institute of Mechanics of the Chinese Academy of Sciences, has been in progress since 2018.

The wind tunnel, with a length of 167 meters, a nozzle exit of 2.5 meters, and a test cabin diameter of four meters, has achieved comprehensive performance parameters at world-leading levels. Capable of testing airflows at speeds of three to 10 kilometers per second, or up to Mach 30, the JF-22 wind tunnel will significantly contribute to the development of China’s aerospace transport systems and hypersonic aircraft.

The combination of the JF-22 and the previously developed JF-12 reproduction wind tunnel creates a ground experimental platform covering all flight ranges for near-space aircraft. The development of hypersonic aircraft is expected to have both military and civilian applications, revolutionizing transportation by significantly reducing travel time across the globe.

 

Indan Infrastructure

India is also developing an indigenous hypersonic cruise missile as part of its Hypersonic Technology Demonstrator Vehicle program and successfully tested a Mach 6 scramjet in June 2019. India operates approximately 12 hypersonic wind tunnels and is capable of testing speeds of up to Mach 13.

 

Satish Dhawan Wind Tunnel Complex Commissioned at VSSC

In the quest to reduce the cost of access to space and to extend the frontiers of space exploration, ISRO has ventured into Reusable Launch Vehicle (RLV) and Re-entry missions, Air-breathing propulsion technology demonstration and Interplanetary missions. These missions encounter design criticalities at Hypersonic Mach number regime and need rigorous aero-thermodynamic characterisation at these Mach numbers. In order to cater to the above need, Industrial type Hypersonic Wind Tunnel and Shock Tunnel have been established at Vikram Sarabhai Space Centre (VSSC).

The hypersonic wind tunnel uses an intermittent blowdown system to simulate flight conditions, blowing air at hypersonic speeds for short periods at regular intervals. It consists of various subsystems such as a high-pressure system, wind tunnel system, nozzle, test section, and vacuum chamber.

The first phase of the facility, commissioned in 2012, features a Mach 6 system and a shock tunnel that have been extensively utilized for ongoing programs at the Indian Space Research Organisation (ISRO). The second phase includes the realization of Mach 8, 10, and 12 nozzles, heating systems, shut-off valves, and cooling systems. The realization of these systems involved intricate design, precision machining, fabrication of high-performance materials, and the development of state-of-the-art components.

With a capability of up to Mach 12 operation, the hypersonic wind tunnel at VSSC is the third-largest in the world in terms of hypersonic flow simulation. It can simulate flow field conditions at Mach 6, 8, 10, and 12 with a nominal nozzle exit diameter of 1 meter. The tunnel operates on a pressure-vacuum system and utilizes a regenerative storage heater to preheat compressed air before it is expanded through the nozzle. Data acquisition and control are facilitated by a programmable logic controller-based system.

The commissioning of these facilities has enabled indigenous development in areas such as cored bricks, hot shut-off valves, and massive forgings. The complex consists of 500 valves, 2 km of pipelines, and various electric motors and fluid pumps. These facilities have been designed and developed with the support of Indian industries.

This state-of-the-art facility will play a crucial role in advancing India’s space exploration endeavors and reducing the cost of access to space.

 

 

 

Other Countries

In addition to the Woomera Test Range facilities one of the largest weapons test facilities in the world Australia operates seven hypersonic wind tunnels and is capable of testing speeds of up to Mach 30. France operates five hypersonic wind tunnels and is capable of testing speeds of up to Mach 21. Germany operates three hypersonic wind tunnels and is capable of testing speeds of up to Mach 11. The Japan Aerospace Exploration Agency operates three hypersonic wind tunnels, with two additional facilities at Mitsubishi Heavy Industries and the University of Tokyo. Other countries including Iran, Israel, and South Korea have conducted foundational research on hypersonic airflows and propulsion systems, but may not be pursuing a hypersonic weapons capability at this time.

 

Technological Advancements:

The power of hypersonic wind tunnels extends beyond military implications. The technologies developed in these testing grounds have wide-ranging applications across various industries. For instance, hypersonic flight has the potential to revolutionize space exploration and transportation. The ability to transport payloads and passengers at unprecedented speeds could significantly reduce travel time, open up new possibilities for scientific research, and enable faster satellite deployment.

Additionally, hypersonic wind tunnels drive technological breakthroughs in materials science and engineering. The extreme conditions experienced during hypersonic flight require materials that can withstand intense temperatures, pressures, and stresses. Researchers utilize wind tunnels to test and develop innovative materials capable of withstanding the extreme environments of hypersonic flight, thereby advancing the broader field of materials science.

 

Conclusion:

Hypersonic wind tunnels serve as crucial infrastructure, providing testing grounds for the development of future hypersonic platforms and technologies. The geopolitical military implications are profound, with nations vying for dominance in this new era of warfare. These facilities also fuel technological advancements that extend beyond the military realm, impacting space exploration, transportation, and materials science. As the race for hypersonic supremacy intensifies, the power of hypersonic wind tunnels will continue to shape the trajectory of military capabilities and technological progress, heralding a new era of speed and innovation.

 

References and resources also include:

https://www.isro.gov.in/satish-dhawan-wind-tunnel-complex-commissioned-vssc

https://www.airforce-technology.com/news/arnold-afb-propulsion-facility/

https://phys.org/news/2018-11-tunnel-lasers-hypersonic-ground-sandia.html

https://www.everycrsreport.com/files/20200317_R45811_1e4d2084a7518e06a80a088da796d084f7232fc0.html

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