y+ Value in CFD: Theory, Free Calculator & Why It Matters
You can build a beautiful mesh, choose a respected turbulence model, run for three days on a cluster — and still get drag wrong by 30%. Very often the culprit is a single number that beginners overlook and experts obsess over: y⁺ . It decides whether your turbulence model is even being used correctly, and it is set before you ever press "solve". This guide covers the full theory of y⁺, gives you a free first-cell-height calculator (validated against published data), and shows exactly how to choose, achieve, and verify the right value for your simulation. Figure 1. The turbulent boundary layer is not uniform. y⁺ tells you which of these zones your first cell centre lands in — and that determines which near-wall model is valid. Table of Contents The y⁺ / First Cell Height Calculator What Is y⁺? (Theory) Structure of the Boundary Layer Why y⁺ Matters So Much The Formula, Step by Step Target y⁺ for Each Turbulence Model The ...