📋 Case Study

Small-Scale Marine Hydrodynamics Implementation

Limited resources and tight budget

🏗️ Project Overview

Design and validation of a low-cost miniature flow tank (L=1.2m, H=0.4m, W=0.3m) for university-level marine hydrodynamics research, enabling PIV measurements and CFD validation for small craft hull form optimization with a total budget under $8,000.

🎯 Challenge

University research team needed experimental hydrodynamics capability for catamaran hull optimization but lacked access to conventional towing tanks (>$2M). Required Reynolds number similarity at model scale (Re ≈ 3×10⁵) while maintaining free-surface effects within a compact laboratory footprint.

🔧 Design Approach

Modular acrylic flow tank with recirculating system: 0.75 kW centrifugal pump, honeycomb flow straightener, and 50μm tracer particles for 2D PIV. Open-source OpenFOAM RANS solver (k-ω SST turbulence model) validated against experimental velocity profiles. Budget-constrained sensor suite: single LaVision NanoLite Nd:YAG laser ($3.2K), two Phantom v711 CMOS cameras ($2.8K pair), and Arduino-based synchronization ($200).

📐 Key Calculations

Reynolds Number (model scale)

Re = VL/ν, V=0.27 m/s, L=1.2m

Result: 3.2 × 10⁵

Ensures turbulent flow regime matching full-scale Froude similarity

Froude Number

Fr = V/√(gL)

Result: 0.35

Free-surface effects properly scaled for wave-making resistance

Boundary Layer Thickness

δ = 0.37x/Re_x^0.2

Result: 8.2 mm

Determines PIV window placement and camera field-of-view requirements

Pump Head Requirement

H = fL/D × V²/2g + ΣK×V²/2g

Result: 0.85 m

Ensures uniform flow velocity within ±2% across test section

📊 Results

Achieved velocity uniformity of ±1.5% across 800mm test section. PIV measurements agreed with OpenFOAM predictions within 4% for mean velocity profiles and 8% for Reynolds stress distributions. Successfully identified optimal catamaran demihull separation (S/L = 0.22) reducing total resistance by 12% compared to monohull baseline. Total project cost: $7,400.

💡 Lessons Learned

•Honeycomb element aspect ratio >6:1 is critical for turbulence intensity <1% at test section inlet
•Acrylic wall thickness must account for hydrostatic pressure + safety factor of 4:1 at 0.4m water depth
•Tracer particle buoyancy correction needed for long-duration runs (>30 min) — hollow glass spheres (ρ=1.05) outperformed polyamide
•OpenFOAM mesh independence study required minimum 2.4M cells for y+<1 at model-scale Reynolds numbers
•Side-wall boundary layer interference can be corrected using wake-similarity method with <3% error

✅ Key Takeaways

1University-scale hydrodynamics labs are feasible under $10K with modern open-source CFD and consumer-grade cameras
2PIV accuracy at small scale is limited by seeding density — minimum 5-8 particles per interrogation window (32×32 px)
3Froude scaling demands careful attention to both Reynolds and Weber number effects when surface tension becomes significant at model scale