{"history":[],"article":{"id":"07e24802-9b37-4342-8c83-e42aec3a74a6","title":"Subsonic and transonic wind tunnel","slug":"subsonic-and-transonic-wind-tunnel","content":":::summary\n:::\n\n# \n**Subsonic wind tunnels** are used for operations at low [Mach numbers](https://bliptext.com/articles/mach-number), with speeds in the test section up to 480 km/h (~ 134 m/s, M = 0.4).\nThey may be of open-return type (also known as the [Eiffel](https://bliptext.com/articles/gustave-eiffel) type) or closed-return flow (also known as the [Prandtl](https://bliptext.com/articles/ludwig-prandtl) type).\nThese tunnels use large [axial fans](https://bliptext.com/articles/axial-fan) to move air and increase dynamic pressure, overcoming viscous losses.\nThe design principles of subsonic wind tunnels are based on the [continuity equation](https://bliptext.com/articles/continuity-equation) and [Bernoulli's principle](https://bliptext.com/articles/bernoulli-s-principle), which allow for the calculation of important parameters such as the tunnel's contraction ratio.\n**Transonic wind tunnels** (0.75 < M < 1.2) are designed on similar principles as subsonic tunnels but present additional challenges, primarily due to the reflection of [shock waves](https://bliptext.com/articles/shock-wave) from the walls of the test section.\nTo mitigate this, perforated or slotted walls are used to reduce shock reflection.\nIn transonic testing, both [Mach number](https://bliptext.com/articles/mach-number) and [Reynolds number](https://bliptext.com/articles/reynolds-number) are critical and must be properly simulated.\nThis often necessitates the use of large-scale facilities and/or [pressurized](https://bliptext.com/articles/pressurized-wind-tunnel) or [cryogenic wind tunnels](https://bliptext.com/articles/cryogenic-wind-tunnel).\nThese tunnels are crucial for studying aerodynamic properties of objects at speeds approaching and surpassing the [speed of sound](https://bliptext.com/articles/speed-of-sound), such as high-speed aircraft and spacecraft during critical phases of flight.\n\n# Low subsonic tunnel\nLow-speed wind tunnels are used for operations at very low [Mach number](https://bliptext.com/articles/mach-number), with speeds in the test section up to 480 km/h (~ 134 [m/s](https://bliptext.com/articles/metre-per-second), [M](https://bliptext.com/articles/mach-number) = 0.4).\nThey may be of open-return type (also known as the [Eiffel](https://bliptext.com/articles/gustave-eiffel) type, [see figure](https://bliptext.com/articles/image-windtunnel1-en-svg)), or closed-return flow (also known as the [Prandtl](https://bliptext.com/articles/prandtl) type, [see figure](https://bliptext.com/articles/image-windtunnel1-en-svg)) with air moved by a propulsion system usually consisting of large axial fans that increase the dynamic pressure to overcome the [viscous](https://bliptext.com/articles/viscosity) losses.\n\n## Open wind tunnel\nThe working principle is based on the continuity and [Bernoulli's equation](https://bliptext.com/articles/bernoulli-s-equation):\nThe continuity equation is given by:\nThe Bernoulli equation states:-\nPutting Bernoulli into the continuity equation gives:\nThe contraction ratio of a windtunnel can now be calculated by:\n# [Schematic of an open wind tunnel with a closed test section | upload.wikimedia.org/wikipedia/commons/b/b8/Windtunnel1-en.svg]\n\n## Closed wind tunnel\nIn a return-flow wind tunnel the return duct must be properly designed to reduce the pressure losses and to ensure smooth flow in the test section.\nThe compressible flow regime:\nAgain with the continuity law, but now for isentropic flow gives:\nThe 1-D area-velocity is known as:\nThe minimal area A where M=1, also known as the sonic throat area is than given for a perfect gas:\n# [Schematic of a closed (return-flow) wind tunnel | upload.wikimedia.org/wikipedia/commons/0/0f/Windtunnel3-en.svg]\n\n# Transonic tunnel\nHigh subsonic wind tunnels (0.4 < M < 0.75) and transonic wind tunnels (0.75 < M < 1.2) are designed on the same principles as the subsonic wind tunnels.\nThe highest speed is reached in the test section.\nThe Mach number is approximately 1 with combined subsonic and supersonic flow regions.\nTesting at transonic speeds presents additional problems, mainly due to the reflection of the shock waves from the walls of the test section (see figure below or enlarge the thumb picture at the right).\nTherefore, perforated or slotted walls are required to reduce shock reflection from the walls.\nSince important viscous or inviscid interactions occur (such as shock waves or boundary layer interaction) both Mach and Reynolds number are important and must be properly simulated.\nLarge-scale facilities and/or pressurized or cryogenic wind tunnels are used.\n# [Experimental rhombus variation with the Mach number | upload.wikimedia.org/wikipedia/commons/1/1c/Tunnelreflection-en.svg]\n\n# de Laval nozzle\nWith a sonic throat, the flow can be accelerated or slowed down.\nThis follows from the 1D area–velocity equation.\nIf an acceleration to supersonic flow is required, a convergent-divergent [nozzle](https://bliptext.com/articles/nozzle) is required.\nOtherwise:\nConclusion: The Mach number is controlled by the expansion ratio","current_revision":null,"created_by":"kACnuQmH5k9Nr5VNVEpVeg7XpvUmMctD","created_at":"2025-01-26T06:59:58.320Z","updated_at":"2025-01-26T06:59:58.320Z","search_vector":"'subson':1 'transon':3 'tunnel':5 'wind':4","search_content":" \n \n\n# \n**Subsonic wind tunnels** are used for operations at low [Mach numbers](https://bliptext.com/articles/mach-number), with speeds in the test section up to 480 km/h (~ 134 m/s, M = 0.4).\nThey may be of open-return type (also known as the [Eiffel](https://bliptext.com/articles/gustave-eiffel) type) or closed-return flow (also known as the [Prandtl](https://bliptext.com/articles/ludwig-prandtl) type).\nThese tunnels use large [axial fans](https://bliptext.com/articles/axial-fan) to move air and increase dynamic pressure, overcoming viscous losses.\nThe design principles of subsonic wind tunnels are based on the [continuity equation](https://bliptext.com/articles/continuity-equation) and [Bernoulli's principle](https://bliptext.com/articles/bernoulli-s-principle), which allow for the calculation of important parameters such as the tunnel's contraction ratio.\n**Transonic wind tunnels** (0.75 < M < 1.2) are designed on similar principles as subsonic tunnels but present additional challenges, primarily due to the reflection of [shock waves](https://bliptext.com/articles/shock-wave) from the walls of the test section.\nTo mitigate this, perforated or slotted walls are used to reduce shock reflection.\nIn transonic testing, both [Mach number](https://bliptext.com/articles/mach-number) and [Reynolds number](https://bliptext.com/articles/reynolds-number) are critical and must be properly simulated.\nThis often necessitates the use of large-scale facilities and/or [pressurized](https://bliptext.com/articles/pressurized-wind-tunnel) or [cryogenic wind tunnels](https://bliptext.com/articles/cryogenic-wind-tunnel).\nThese tunnels are crucial for studying aerodynamic properties of objects at speeds approaching and surpassing the [speed of sound](https://bliptext.com/articles/speed-of-sound), such as high-speed aircraft and spacecraft during critical phases of flight.\n\n# Low subsonic tunnel\nLow-speed wind tunnels are used for operations at very low [[M](https://bliptext.com/articles/mach-number)ach number](https://bliptext.com/articles/mach-number), with speeds in the test section up to 480 km/h (~ 134 [m/s](https://bliptext.com/articles/metre-per-second), [M](https://bliptext.com/articles/mach-number) = 0.4).\nThey may be of open-return type (also known as the [Eiffel](https://bliptext.com/articles/gustave-eiffel) type, [[see figure](https://bliptext.com/articles/image-windtunnel3-en-svg)](https://bliptext.com/articles/image-windtunnel1-en-svg)), or closed-return flow (also known as the [Prandtl](https://bliptext.com/articles/prandtl) type, [[see figure](https://bliptext.com/articles/image-windtunnel3-en-svg)](https://bliptext.com/articles/image-windtunnel1-en-svg)) with air moved by a propulsion system usually consisting of large axial fans that increase the dynamic pressure to overcome the [viscous](https://bliptext.com/articles/viscosity) losses.\n\n## Open wind tunnel\nThe working principle is based on the continuity and [Bernoulli's equation](https://bliptext.com/articles/bernoulli-s-equation):\nThe continuity equation is given by:\nThe Bernoulli equation states:-\nPutting Bernoulli into the continuity equation gives:\nThe contraction ratio of a windtunnel can now be calculated by:\n# [Schematic of an open wind tunnel with a closed test section | upload.wikimedia.org/wikipedia/commons/b/b8/Windtunnel1-en.svg]\n\n## Closed wind tunnel\nIn a return-flow wind tunnel the return duct must be properly designed to reduce the pressure losses and to ensure smooth flow in the test section.\nThe compressible flow regime:\nAgain with the continuity law, but now for isentropic flow gives:\nThe 1-D area-velocity is known as:\nThe minimal area A where M=1, also known as the sonic throat area is than given for a perfect gas:\n# [Schematic of a closed (return-flow) wind tunnel | upload.wikimedia.org/wikipedia/commons/0/0f/Windtunnel3-en.svg]\n\n# Transonic tunnel\nHigh subsonic wind tunnels (0.4 < M < 0.75) and transonic wind tunnels (0.75 < M < 1.2) are designed on the same principles as the subsonic wind tunnels.\nThe highest speed is reached in the test section.\nThe Mach number is approximately 1 with combined subsonic and supersonic flow regions.\nTesting at transonic speeds presents additional problems, mainly due to the reflection of the shock waves from the walls of the test section (see figure below or enlarge the thumb picture at the right).\nTherefore, perforated or slotted walls are required to reduce shock reflection from the walls.\nSince important viscous or inviscid interactions occur (such as shock waves or boundary layer interaction) both Mach and Reynolds number are important and must be properly simulated.\nLarge-scale facilities and/or pressurized or cryogenic wind tunnels are used.\n# [Experimental rhombus variation with the Mach number | upload.wikimedia.org/wikipedia/commons/1/1c/Tunnelreflection-en.svg]\n\n# de Laval nozzle\nWith a sonic throat, the flow can be accelerated or slowed down.\nThis follows from the 1D area–velocity equation.\nIf an acceleration to supersonic flow is required, a convergent-divergent [nozzle](https://bliptext.com/articles/nozzle) is required.\nOtherwise:\nConclusion: The Mach number is controlled by the expansion ratio","revisionCount":0},"hasMore":false,"nextCursor":null}

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