The University of Wisconsin–Madison College of Engineering now operates a large-scale, low-speed, closed-circuit wind tunnel that serves as a core experimental facility for fundamental and applied fluid mechanics research. Originally conceived to address the absence of a high-capability wind tunnel on campus, the facility has matured into a research-grade experimental platform supporting cutting-edge investigations in turbulence, aerodynamics, and aeroacoustics.

The wind tunnel features a 4 ft × 3 ft (1.22 m × 0.91 m) test section and is capable of operating at freestream velocities of up to 62 m/s, providing Reynolds numbers well beyond those achievable in prior UW–Madison facilities. These capabilities have already enabled experiments that directly address scale effects, turbulent boundary layers, and flow–structure interactions relevant to aerospace, energy, and transportation systems. The free-stream turbulence intensity has been estimated to be 0.22%. 

To further expand its research reach, the tunnel is currently being extended to a total test-section length of 10 m, a transformative enhancement that enables high-Reynolds-number flows with fully developed turbulence. The extended test section allows for longer development lengths, reduced inlet-condition sensitivity, and more faithful representation of real-world flow physics. This upgrade positions the facility to address longstanding challenges in high-Reynolds-number turbulence, including scale separation, intermittency, and anisotropy, which are difficult or impossible to study in smaller laboratory tunnels.

The closed-circuit configuration remains a defining strength of the facility. By recirculating flow, the tunnel achieves high flow quality and energy efficiency, allowing for sustained high-speed operation with manageable power requirements and thermal loads. This design is particularly critical for aeroacoustic research, where background noise levels, flow uniformity, and long run times are essential for resolving low-amplitude sound generation mechanisms.

Current and Future Research Applications

The wind tunnel is now actively used for:

• High-Reynolds-number turbulence research, including boundary-layer development, coherent structures, and energy cascades

• Aeroacoustic studies, focusing on flow-induced noise, wall-pressure fluctuations and . 

• Unsteady Aerodynamics Studying the impact of incoming turbulence, using active grid, on flow separation, tip leakage vortex and laminar separation bubble and their recovery.

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The wind tunnel is embedded within a well-equipped experimental fluid mechanics laboratory that enables comprehensive, multi-modal measurements of velocity, turbulence, wall loading, and acoustic response. Available diagnostics include:

• Hot-wire anemometry for high-frequency, pointwise measurements of velocity fluctuations and turbulence spectra

• Particle Image Velocimetry (PIV) system from LaVision® .

• Microphone arrays and acoustic sensors for aeroacoustic source characterization and flow-noise coupling studies

• Wall-shear-stress sensors for direct measurement of near-wall turbulence dynamics and boundary-layer development

The combination of a large test section, long streamwise development length, and advanced instrumentation allows simultaneous measurement of velocity fields, wall shear, and radiated sound, enabling experiments that directly link turbulent flow structures to aerodynamic loading and noise generation.

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The laboratory is equipped with Fused Deposition Modeling (FDM) from Bambu Labs and Stereolithography (SLA) resin 3D printers, which are used for the rapid fabrication of airfoils, aerodynamic models, and custom small-scale components for experimentation. These in-house 3D printing capabilities enable fast design–test–iterate cycles, allowing experimental geometries to be modified and redeployed within days rather than weeks.

FDM printing is used for robust, structurally stable models and mounting hardware, while SLA resin printing provides high-resolution surface finish suitable for aerodynamic surfaces, flow-control devices, and sensor housings where geometric fidelity is critical. The ability to rapidly manufacture and refine test articles directly supports high-Reynolds-number turbulence and aeroacoustic experiments by reducing lead time, increasing experimental throughput, and enabling systematic parametric studies.