Laboratory 2: Fluid Mechanics Simulation Study Notes

Laboratory 2 Alternate Introduction to Simulation – Fluid Mechanics

• Date: January 16, 2026
• Version: 0.28
• Instructor: P.D. Washabaugh
• Courses: Eng 100-700 and Aero 205

Purpose

• Introduce aspects of fluid simulation and testing.
• Familiarize students with a commercially available simulation tool.
• Understand internal flows of the hovercraft.
• Approximate hovercraft's overall lift performance.

Key Concepts

• Fluid Simulation
• Conservation of mass, momentum, and energy
• Bernoulli’s Equation

Summary

1. Preparation

   • Finish the shell assembly from Lab 1.
   • Modify an air-puck model to simulate internal fluid flow.
   • Study lift performance as a function of input energy.
   • Physical model construction requires cutting struts using a laser-cutter.
   • Testing will involve a power supply and pressure sensors.

2. Instrumentation Required

   • Computer workstation with CFD software
   • Laser cutter
   • Power supply
   • Manometers

3. Operational Notes

   • Sit at Lab 1 stations.
   • Use paper/chipboard/cardboard materials.
   • For other StarCCM+ implementations (e.g., no StarCat 5) refer to the appendix.
   • Individual activities should be turned into demos.

Due Dates

• Preparatory assignment: Due at start of lab section.
• Technical Questions: January 26, 7:00 pm via Canvas.
• Team Questions: January 26, 11:00 pm via Canvas.

Introduction

• Goal: Introduce modern simulation tools.
• Model internal flows in air-cushioned vehicle for increased efficiency.
• Seek regions for component integration without disrupting flow.

Hovercraft Testing

1. Setup

   • Use a built shell with a motor, propeller, and custom-fabricated strut.
   • Engaged instruments to measure plenum pressure and flow speed.
   • Focus: Pressure recovered inside shell and flow escaping from it.

2. Important Parameters

   • Measure pressure needed to determine mass-carrying capability.
   • Assess influence on flight altitude by evaluating the gap size.
   • Analyze overall mass-flow rates from flow speed measurements.

3. Simulation vs. Experiment

   • Simulation: Assumes ideal conditions; perfect geometry.
   • Experiment: Recognizes real-world inefficiencies like leakage and flow non-uniformities.

Conservation Principles

Conservation of Mass

• Continuity Equation: States that mass flow into a system equals mass flow out (no accumulation).
  • M = u1 ho1 A1 = u2
    ho2 A2
  • Assumes density ($
    ho$) remains constant in slow flows.
  • Valid assumption if speeds are below ~200 m/s.

Bernoulli's Equation

• Energy conservation along a streamline with no additional energy input/output.
• Decomposes total energy into static energy, dynamic energy, and potential energy terms:
  • P_T = P + rac{1}{2}
    ho u^2 +
    ho g h
• Definition of various pressure types:
  • Static Pressure: $P_s = P$
  • Dynamic Pressure: P_d = rac{1}{2}
    ho u^2
  • Head (Potential Energy): P_h =
    ho g h
  • Total Pressure: $P<em>T = P</em>s + P<em>d + P</em>h$

Example Calculations

1. Continuity and Velocity Calculation

   • Given an inlet area of 0.01 m², speed of 3 m/s, and an outlet area of 0.005 m², calculate outlet speed:
   • $u<em>2 = u</em>1 \frac{A<em>1}{A</em>2} = 3 \frac{0.01}{0.005} = 6 ext{ m/s}$

2. Bernoulli's Principles

   • Assuming input total pressure of 22.05 kPa, static pressure at inlet: - For dynamic pressure calculations use the equation:
   • Ps = PT - rac{1}{2}
     ho u^2
   • Static Pressure Calculation Example: $P_s = 22.05 kPa - 5.51 kPa = 16.49 kPa$

Pressure and Power

• Description of internal velocity implications around propellers and relationship with mass flow rates to pressure measurement.
• Power input and the efficiency of the motor-propeller system's contribution to system performance must be calculated and monitored over various conditions.

Experimentation Setup

• Define components: spacers, craft structure, and instrumentation for measuring parameters like power supply voltage, plenum pressure, dynamic pressure, etc.
• Ensure pressure sensors read zero at startup, monitor increases in voltage and corresponding pressure metrics.

Notes

• Comprehensive understanding of pressures, mass flow, lift functions during experimentation is essential.
• Continuous adjustment and monitoring of operational parameters to facilitate accurate data acquisition and analysis.

Procedure for Experimentation

1. Initialization of power supply and sensors.
2. Systematic increase in power voltage and recording of respective pressure measurements.
3. Daily analysis of lift performance comparing simulation and experimental models at various velocities and configurations.

Conclusion

• Summation of expected outcomes based on computed pressures at specific inlet velocities, leading to estimations of lift.
• Necessary adjustments to methods/approaches based on comparative analyses of simulation data vs. actual performance measurements.