RYURAKU - Fluid Dynamics

RYURAKU is an interactive educational simulation app for experiencing fluid dynamics phenomena firsthand.

Developer: Fuji Bit Inc.

The 6th title in the SUUGAKU / BUTURAKU / DENRAKU / HARAKU / NETURAKU series. The theme is "flow." Discover the wonders of fluid physics through 12 hands-on simulations.

12 simulations in 3 categories:

- Flow basics
- Streamlines: particles reveal potential flow around a cylinder in a uniform stream. Drag the obstacle and watch the flow field change in real time.
- Bernoulli's Principle: flow through a Venturi tube with live pressure gauges. Watch speed rise and pressure drop where the pipe narrows, and see A1v1 = A2v2 at work.
- Reynolds Number: laminar-turbulent transition in pipe flow. Adjust speed, viscosity and diameter and see the dramatic change at Re ≈ 2300.
- Boundary Layer: a boundary layer growing over a flat plate, from the laminar Blasius solution to turbulent transition at Re_x ≈ 5×10^5.
- Darcy's Law: slow flow through porous media such as sand or rock. Adjust permeability, pressure gradient and porosity to experience q = (k/μ)·∇P, the law behind groundwater, oil reservoirs and filters.

- Vortices & lift
- Vortex: point vortices and their mutual induction. Tap to add a counterclockwise vortex, long-press for clockwise.
- Kármán Vortex Street: alternating vortex shedding behind a cylinder, with live Strouhal and Reynolds numbers.
- Lift Force: flow around an airfoil and how lift and drag arise. Change the angle of attack or camber and watch the force vectors.
- Magnus Effect: asymmetric flow and a sideways force on a spinning cylinder: the physics of curveballs and banana kicks.

- Water & gravity
- Buoyancy (new): Archimedes' principle. Change the object and fluid densities to find where things float, sink or hang in balance. Drag the object under, let go, and watch it bob until it settles with a submerged fraction of ρ_s/ρ_f.
- Torricelli's Law (new): water jetting from a hole in a tank. See the exit speed v = √(2gh), the falling water level and the jet range R = 2√(y₀h). Drag the hole to find the height that throws the water farthest.
- Surface Wave: free-surface gravity waves. As the depth-to-wavelength ratio changes, particle orbits shift smoothly from circles (deep water) to flattened ellipses (shallow water).

Features:
- Real-time parameter adjustment for every simulation
- A hint on how to try each screen, plus an explanation with formulas
- Live physics formulas and values
- Works with large text sizes, landscape, iPad and Split View
- Taps and drags can also be done with buttons and sliders (works with VoiceOver and Switch Control)
- 16 languages (English, Japanese, Chinese Simplified / Traditional, Korean, Spanish, Portuguese, German, French, Hindi, Indonesian, Russian, Italian, Turkish, Thai, Vietnamese)
- Dark mode / Light mode

Pricing & ads:
- Free. No in-app purchases, subscriptions or paid unlocks
- A banner ad (Pangle) is shown at the bottom of the screen
- Ads are personalized only if you allow tracking (ATT). You can also turn off personalized ads from "About this app" > "Ad settings"

Recommended for:
- Students studying fluid dynamics in physics class
- Anyone who wants to understand how flow behaves
- Teachers looking for interactive teaching materials
- Anyone interested in aeronautics or fluid mechanics