CHT – Derived Heat Flux on Inner Cylinder Wall Gives Unrealistically Low Temperatures

Using SimScale Thermal
1

Hi everyone,

I am simulating a high-pressure compressor cylinder (80 → 350 bar, bore 14 mm, stroke 50 mm) in a steady-state CHT setup in SimScale. Since I cannot model the actual compression cycle, I pre-calculated cycle-averaged values for hh and TrefTref using the Woschni correlation and applied them as External Wall Heat Flux → Derived Heat Flux BCs across 20 axial zones on the inner cylinder wall. The cylinder is cooled externally by a fan (Velocity Inlet, 11 m/s).

Problem: The simulation converges but gives wall temperatures of only ~30°C — barely above ambient. Analytically, I would expect ~80–95°C based on the balance between hihi = 656 W/m²K (TrefTref = 108°C) and hehe ≈ 99 W/m²K from the fan.

2

I think your result (~30°C wall temperature) is almost certainly caused by the way the “Derived Heat Flux” BC is being interpreted in SimScale.

3

From looking at the project, it sounds like you were able to figure out the issue with temperatures. Could you expand a bit on what was done? Thanks.