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Airfoil

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An airfoil is the cross-section of a wing, blade, rudder or foil, shaped to produce lift with as little drag as possible. The same theory applies in air and in water, from aircraft wings and wind turbine blades to ship rudders, keels and hydrofoils. This post covers the fundamentals, the key equations, a worked wing example and the checks that keep airfoil estimates useful in design. Aircraft model in the NASA Ames 40x80 ft wind tunnel. Photo: NASA Ames Research Center / NASA , Public domain via Wikimedia Commons Airfoil Fundamentals A flowing fluid creates lift on an airfoil because the pressure on the lower surface is higher than on the upper surface. Equivalently, the airfoil generates circulation around itself. The sharp trailing edge fixes the flow there (the Kutta condition), which sets the amount of circulation and therefore the lift. Term Meaning Chord (c) Straight-line distance from leading edge to trailing edge Camber Curvature of the mean line, which gives lift at ...
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External Flow

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External flow is flow over the outside of a body: wind around a stack, air over a pipe rack, current past a pile, or air across a vehicle. The key questions are how much force the fluid applies and whether it excites vibration. This post covers the fundamentals, the key equations, a worked wind-load example and the checks that keep external flow estimates useful in design. Karman vortex street forming in clouds behind Rishiri Island, Japan. Photo: NASA , Public domain via Wikimedia Commons External Flow Fundamentals When fluid meets a body, a thin boundary layer forms on its surface. Inside the layer, velocity rises from zero at the wall to the free-stream value. Two mechanisms produce drag. Skin friction drag: shear stress along the surface. It dominates for streamlined bodies and flat plates aligned with the flow. Pressure (form) drag: a pressure imbalance between the front and the wake. It dominates for bluff bodies such as cylinders, plates facing the flow and most structur...
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Internal Flows

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Internal flow is flow confined by solid walls, most commonly liquid or gas moving through pipes, ducts and channels. It sets pump and compressor duty, line sizes, control valve ranges and many of the loads piping must carry. This post covers the fundamentals, the key equations, a worked pressure drop and pump power example, and the checks that keep a hydraulic calculation reliable. The Trans-Alaska Pipeline, a classic internal-flow system. Photo: Luca Galuzzi (Lucag) , CC BY-SA 2.5 via Wikimedia Commons Internal Flow Fundamentals As fluid enters a pipe, a boundary layer grows from the wall until it fills the cross-section. Beyond this entrance region the flow is fully developed and the velocity profile no longer changes along the pipe. The profile depends on the flow regime, which is set by the Reynolds number, Re = ρVD/μ. Laminar flow (Re below about 2,300): smooth layers with a parabolic profile, where maximum velocity is twice the average. Transitional flow (about 2,300 to 4,...
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Convective Heat Transfer

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Convective heat transfer is the exchange of heat between a surface and a moving fluid. It sets the performance of heat exchangers, cooling coils, ducts, electrical enclosures, boilers and process lines. The physics is straightforward in principle, but the heat transfer coefficient depends on flow regime, geometry and fluid properties. This post explains the fundamentals, the key equations, a worked example and the checks that keep a calculation reliable. Air-cooled heat exchangers at the Molten Salt Reactor Experiment. Photo: Oak Ridge National Laboratory via Wikimedia Commons (U.S. government work, public domain). Convective Heat Transfer Fundamentals Convection combines two mechanisms: conduction through the fluid layer next to the surface, and bulk fluid motion that carries energy away. Near a wall, the fluid forms a thin boundary layer where velocity and temperature change steeply. The thinner the layer, the higher the heat transfer. The rate is described by Newton's law o...
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Heat Exchangers

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Heat exchangers move thermal energy from one fluid to another without letting the fluids mix. They sit in nearly every process, power and utility system, from crude preheat trains to lube oil coolers. Getting one right means getting the thermal duty, the pressure drop and the mechanical design right together. This post covers the fundamentals, the key equations, a worked sizing example and the checks engineers apply before releasing a design. Tube bundle of a shell-and-tube heat exchanger. Photo by Alnitak3/Wikimedia Commons , licensed CC BY-SA 4.0 . Heat Exchanger Fundamentals Heat flows from the hot stream through a wall to the cold stream. Three resistances act in series: convection on the hot side, conduction through the tube or plate wall, and convection on the cold side. Fouling layers add resistance on each surface over time. The designer's job is to provide enough surface area to transfer the required duty with acceptable pressure drop and cost. Type Strengths Limits...
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Marine Engineering and Naval Architecture: Stability, Loads and Design Workflow

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A vessel or floating structure has to float upright, move through water efficiently, survive the sea and satisfy a class society before it can sail. Each of those requirements is a naval architecture problem, and they interact. This post explains the core calculations and the design workflow behind marine engineering and naval architecture services, from stability to class approval. Underwater hull form of the SS Great Britain in dry dock. Photo: Nortix08 , CC BY-SA 4.0 via Wikimedia Commons Intact Stability and GM Intact stability describes a vessel's ability to return upright after a heel disturbance. The starting measure is the metacentric height, GM = KM − KG , where KM = KB + BM and BM = I / ∇ (waterplane second moment of area divided by displaced volume). The GZ curve then shows the righting lever across all heel angles. Its shape matters more than GM alone. Worked example. A box barge is 40 m long, 10 m wide, floats at a 2 m draft and has KG = 3.0 m. Displaced volume ∇...
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Solar PV Engineering Design: Yield, Structures and Grid Connection

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Solar PV looks simple on paper: modules, inverters, cables and a grid connection. In practice, the energy a plant delivers depends on decisions made in design: how irradiance is modelled, how strings are sized, how the structure resists wind and how the plant meets grid requirements. This post follows the main steps of solar PV engineering design, from site assessment to final deliverables. Ground-mounted PV arrays at a solar farm near Vulcan, Alberta. Photo: Kkiefuik , CC BY 4.0 via Wikimedia Commons Site Assessment and Irradiance Data Design starts with the site. Irradiance data sets the energy yield, and site conditions set cost and risk. Gather the following early: Irradiance and weather: GHI, DNI and diffuse data from satellite-derived sources such as Meteonorm, PVGIS or Solargis, ideally checked against on-site pyranometer measurements for financing. Temperature, wind, snow, humidity and dust: these drive losses and structural loads. Terrain and shading: slope, horizon p...
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