Enter the jet velocity, jet thickness, surface radius of curvature (or curvature), and fluid density to estimate the pressure difference needed to curve a jet along a surface (a simplified radial-equilibrium scaling). Optionally, enter an available pressure difference to estimate the minimum velocity.
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Coanda Effect Formula
The Coandă effect is a flow phenomenon and does not have a single universal “one-size-fits-all” equation. However, for a thin jet following a curved surface, a commonly used radial-equilibrium scaling can estimate the pressure difference needed to bend the jet along a radius of curvature.
( \Delta p \approx \rho V^2 b K = \rho V^2 \frac{b}{R} )Variables:
- Δp is the estimated pressure difference across the jet thickness (Pa)
- ρ is the fluid density (kg/m³)
- V is the jet (fluid) velocity (m/s)
- b is the jet thickness (m)
- R is the radius of curvature of the streamline path (m)
- K is curvature (1/m), where K = 1/R
To estimate the pressure difference needed to curve a thin jet, multiply ρV² by the thickness-to-radius ratio b/R (equivalently, multiply by b·K). This is a simplified scaling; real Coandă attachment also depends on geometry, turbulence/entrainment, viscosity, surface roughness, and nearby boundaries.
What is the Coanda Effect?
The Coandă Effect is the tendency of a fluid jet to be attracted to and follow a nearby surface. This phenomenon occurs when a fluid stream, such as air or water, follows the contour of a nearby surface rather than continuing in its initial direction. The effect is named after Romanian engineer Henri Coandă, who described and popularized it in the 1930s (with related observations dating back earlier). The Coandă Effect is utilized in various engineering applications, including blown/fluidic flow-control devices, some aircraft high-lift concepts, and HVAC systems, to influence and direct fluid flow.
How to Calculate Coanda Effect?
The following steps outline one simplified way to estimate the pressure difference associated with curving a thin jet along a surface.
- Determine the jet velocity (V).
- Determine the jet thickness (b).
- Determine the radius of curvature (R) of the surface/streamline path (or curvature K = 1/R).
- Determine the fluid density (ρ).
- Estimate the pressure difference using Δp ≈ ρV²(b/R).
- After inserting the values and calculating the result, compare your estimate with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
Fluid Velocity (V) = 10 m/s
Fluid Density (ρ) = 1.20 kg/m³, Jet Thickness (b) = 0.02 m, Radius of Curvature (R) = 0.10 m (K = 10 1/m)
Estimated Pressure Difference (Δp) ≈ ρV²(b/R) = 1.20 × 10² × (0.02/0.10) = 24 Pa