Wind Tunnel

(In progress)

The Wind Tunnel project is an ongoing effort to design and build a compact, open-loop aerodynamic testing system for educational and experimental use.

Objective

The objective of this project is to design and construct a semi-modular, open-loop wind tunnel capable of accurately measuring aerodynamic forces such as drag, lift, and side forces on scale models. The tunnel will prioritize flow uniformity and repeatable data collection, using integrated Arduino-based sensors to record real-time velocity, pressure, temperature, etc. Designed with mobility and practicality in mind, the system will feature a compact frame that can be easily disassembled for transport and storage while maintaining structural rigidity during operation. CAD modeling and CFD analysis in SolidWorks and ANSYS will guide the optimization of diffuser angles, contraction ratios, and fan placement to achieve smooth, laminar airflow. Once complete, the tunnel will provide a reliable platform for aerodynamic testing, model validation, and hands-on research in fluid dynamics. This project is being developed as part of a larger goal to support future research in vehicle aerodynamics, wing design, and propulsion system efficiency.

Requirements

Goals

Develop a compact open-loop wind tunnel for aerodynamic testing of scale models and vehicle components.
Measure drag and lift using integrated Arduino-based sensors and load cells.
Capture real-time airflow data (velocity, pressure, and temperature) for analysis and calibration.
Achieve test-section airspeeds up to 9 m/s (≈20 mph) under controlled conditions.
Use CFD simulations (SolidWorks / ANSYS) to optimize contraction ratio, diffuser angle, and flow conditioning.
Design a semi-modular frame that can be disassembled for transport and storage.
Incorporate acrylic or polycarbonate panels for optical access and flow visualization (e.g., smoke or tufts).
Power the system with a single high-static-pressure fan, optimized for flow uniformity and noise reduction.
Maintain stable operation for continuous runs up to 5 minutes without overheating or fan instability.
LEARN

Design Development

Initial Concept Calculations

The design process began with establishing key geometric parameters and chamber ratios to achieve smooth, uniform airflow through the test section. Early concept sketches and calculations focused on defining the dimensions of the inlet, contraction, test, and diffuser chambers based on aerodynamic efficiency and manufacturability. A 5th-degree polynomial contraction profile was selected to minimize boundary layer separation and pressure losses, while diffuser walls were angled at 7° to promote stable flow recovery. Each section’s geometry, including inlet area, test section ratio, and chamber lengths, was derived through iterative analysis to balance performance with the constraints of an open-loop system.

CAD Designs

The wind tunnel geometry was modeled and refined in SolidWorks through multiple design iterations, focusing on aerodynamic efficiency, manufacturability, and structural stability. Each stage of development addressed weaknesses observed in previous versions, while preserving smooth flow transitions and modularity for easy transport and upgrades. The models also served as a foundation for CFD analysis, ensuring the final tunnel maintains uniform flow distribution, minimal turbulence, and ease of assembly.

1st Iteration

The initial CAD model established the overall form factor of the open-loop tunnel, including the inlet, contraction, test, and diffuser chambers. This version focused primarily on defining chamber proportions and the curvature of the contraction section. While effective for spatial layout and airflow path visualization, it lacked structural reinforcement and mounting features for sensors, highlighting areas for mechanical and aerodynamic improvement.

2nd Iteration

The second iteration introduced structural bracing to improve rigidity under load and maintain precise alignment between chambers. The flow-conditioning screens were integrated into the design to enhance flow uniformity entering the test chamber. Additional areas were included for installing instrumentation and future upgrades. The base structure acts as both a stand and an area to install electronics and sensors.

Parts List (Changes to be made)

The wind tunnel’s components were carefully selected to balance performance, accuracy, and cost efficiency while maintaining modularity for future upgrades. The current design prioritizes reliable airflow generation, precise aerodynamic measurement, and robust data acquisition using Arduino-based control and sensing systems. Each component, ranging from the high-static-pressure fan to the differential pressure and load sensors, was chosen to ensure repeatable testing conditions and ease of integration with the data collection interface.

Prototyping

Scale Prototype

A 24% scale protype of the wind tunnel prototype was fabricated to validate the CAD model’s geometry, ensuring accurate representation of the contraction, test, and diffuser sections before full-scale construction. A prototype was 3d printed using PLA, allowing for rapid testing of contraction and diffuser transitions as well as assembly fit. The design was scaled proportionally to preserve flow characteristics while minimizing print time and material cost.

3d Print File

The digital slicing stage in the 3D printing workflow defined the orientation, scale, and print supports of the model. The wind tunnel was sectioned and arranged to minimize warping and ensure the contraction and diffuser curves printed cleanly.

3d Printing

Layer adhesion and tolerance testing ensured that the contraction and test chambers could be printed as continuous, sealed volumes. Real-time adjustments to speed, temperature, and support placement improved print quality and minimized post-processing time.

The first assembled prototype was used to evaluate fit, proportion, and airflow pathway alignment. The open-loop tunnel was supported by a lightweight frame that replicated full-scale mounting conditions. This version provided an initial physical sense of scale and helped assess stability and flow uniformity.

The final scaled prototype incorporated reinforced walls, a larger base for stability, and an integrated fan inlet for consistent airflow entry. Its modular structure allows for easy transport and sensor integration during early calibration tests. This version represents the optimized configuration that will inform full-scale fabrication and CFD validation.

Fabrication

Full-Size Build

The fabrication process centered on constructing a structurally stable wind tunnel capable of producing reliable airflow conditions. Key considerations included surface smoothness, contraction shaping, and modular assembly to support iterative testing and mobility. Each stage of development informed refinements, leading to an optimized configuration suitable for experimental validation and comparison with CFD results.

Contraction Cone

Initial Assembly

The contraction cone was constructed using matboard and tape to establish the overall geometry and validate the 5th-degree polynomial contraction profile.

Refined Structure

The contraction section was integrated into a reinforced wooden frame to improve rigidity and maintain the designed contour to preserve a smooth contraction profile for airflow acceleration.

Inside the Cone

The interior of the contraction cone will be "bondo'd" and sanded to provide a smooth, continuous surface following the 5th-degree profile, guiding airflow into the test section.

Air Flow Straightener

Printing Sections

The inlet flow straightener was fabricated using 3D printing in multiple sections due to size constraints.

Assembled Layout

All flow straightener sections were completed and arranged to verify alignment. This step ensured consistency across the array and confirmed proper coverage of the inlet cross-section.

Sections Installed

The flow straightener was integrated into the tunnel inlet to condition incoming airflow. Minor adjustments, including sanding, will help achieve a precise fit and ensure uniform flow distribution into the test section.

Test Section and Data Measurement

Electronic Components

The measurement system is built around an Arduino Nano and includes dual 5lb load cells for lift and drag, load cell amplifiers, a Pitot tube with pressure sensor, and a BME280 for temperature and humidity. These components form the foundation for real-time aerodynamic data acquisition.

Mechanical Integration

The force measurement structure was redesigned to improve load transfer, allowing lift and drag forces to travel more directly to their respective sensors. This refinement reduces unwanted deflection and cross-interference, resulting in more accurate and consistent measurements.

Wiring and Operation

All sensors are integrated through the Arduino Nano to provide real-time accurate data. Data from the BME280 is used to determine air density, allowing accurate airspeed, Reynolds number estimation, and other crucial aerodynamic analysis.

Diffuser

Diffuser Structure

The diffuser section was constructed to gradually expand the flow area, reducing air velocity while recovering static pressure. The expansion geometry was designed with a 7° typical diffuser angle to minimize the risk of flow separation.

Interior View

The internal surface of the diffuser follows a smooth, continuous expansion from the test section outlet. Maintaining surface continuity and controlled divergence helps preserve flow stability and allows effective pressure recovery.

Fan Integration

The diffuser was paired with an external axial fan rated at 2850CFM. As a low static pressure fan, its effective flowrate decreases when upstream components such as flow straighteners and contractions create resistance.

Modularity

Alignment Structure

Custom connector interfaces were fabricated to align and join individual tunnel sections. The design ensures proper positioning between modules and provides a continuous airflow path across section transitions.

Latching Mechanism

Toggle latches were integrated into the connector system to provide secure and repeatable fastening between sections. These latches apply compressive force across the joint, enabling the use of edge sealing material to minimize air leakage. There are connectors on the top and bottom of the structure.

Assmebled Connection

The completed connector system allows the tunnel sections to be rigidly joined while remaining fully modular. When latched, the joints compress sealing material along the edges, creating an airtight interface that preserves flow quality and prevents pressure losses.

Semi-Completed Wind Tunnel (needs bondo and paint)

The completed wind tunnel integrates the contraction section, test section, diffuser, and measurement systems into a fully functional modular setup. Designed for aerodynamic testing and analysis, the system enables controlled airflow, real-time force measurement, and environmental correction for accurate data collection. This final configuration represents the combination of iterative design, fabrication, and refinement, providing a reliable platform for experimental validation and comparison with CFD results.

Testing & Validation

This part of the build is in progress — photos and data will be added once testing is complete.

Results & Analysis

This part of the build is in progress — photos and data will be added once testing is complete.

Potential Improvements

Fan with higher CFM and higher static pressure to better maintain airflow under resistance from the flow straightener, contraction, and test model, especially for higher-speed testing.
More vibration damping between the fan, tunnel structure, and sensor system to reduce noise in force and pressure measurements.
Incorporate additional screens or refined straightener geometry upstream of the contraction to further reduce swirl and improve flow uniformity.
Further stiffen and isolate the lift and drag measurement assembly to reduce cross-interference and improve load transfer directly into the sensors.
Add dedicated differential pressure measurement, additional temperature points, or flow uniformity measurement locations to improve data quality and diagnostic capability.
Add closed-loop fan control to maintain target airflow speed more consistently under changing test conditions.
Improve model mounting and test section accessibility to allow faster setup changes and more repeatable positioning of test articles.
Develop more refined calibration procedures for force and velocity measurements to improve repeatability and confidence in experimental results.

Technical Skills Applied

Mechanical & Design

Designed and developed wind tunnel geometry including contraction cone (5th-degree polynomial profile), test section, and diffuser for controlled airflow behavior.
Engineered modular structural components to ensure alignment, rigidity, and repeatable assembly across sections.
Optimized internal surfaces and transitions to minimize flow separation, leakage, and turbulence.

Fabrication & Manufacturing

Fabricated tunnel structure using wood, matboard, and reinforcement techniques with focus on structural integrity and dimensional accuracy.
Produced multi-part 3D printed flow straighteners within printer constraints and assembled into a full inlet conditioning system.
Implemented sealing strategies at section interfaces using compression latching to reduce air leakage and pressure loss.

Aerodynamics & Flow Control

Applied aerodynamic principles including flow straightening, contraction shaping, and diffuser expansion to achieve uniform test section flow.
Designed within practical diffuser angle limits to minimize separation and improve pressure recovery.
Evaluated airflow performance through iterative physical testing and design refinement.

Instrumentation & Data Acquisition

Integrated dual load cells for lift and drag measurement with dedicated amplification for accurate force sensing.
Implemented Pitot-based pressure measurement system for velocity determination.
Incorporated environmental sensing (temperature, humidity, pressure) to enable real-time air density correction.

Data Analysis & Experimental Validation

Calculated derived aerodynamic parameters including airspeed, air density, Reynolds number, lift, drag, and lift-to-drag ratio.
Correlated experimental results with CFD predictions to evaluate model accuracy and system performance.
Designed and executed controlled test procedures to ensure repeatability and data reliability.

Engineering Process

Applied iterative design methodology to refine mechanical structure, airflow components, and measurement systems.
Identified and resolved issues related to force transmission, airflow uniformity, and system integration.
Managed full system integration from concept through fabrication, testing, and validation.

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