CFD Surrogate Studio — User Manual

1What is CFD Surrogate Studio?

It is a fast reduced-order ("surrogate") model of a mixing vessel. Instead of solving the full Navier–Stokes equations on a million-cell mesh, it uses engineering correlations (power number, flow number, Metzner–Otto shear, Zwietering suspension, etc.) plus a jet-based reduced field solver to estimate the velocity, shear, power, kLa, heat and solids behaviour of your vessel.

23-step quick start

3Input guide (sidebar)

The sidebar is organised as six numbered steps. Ranges below are the exact limits enforced in the app.

Step 1 · Platform

Choose stirred, shaken or rocked. This decides which container families, impellers and result tabs are available.

Step 2 · Container family + geometry

• Container family fixes the footprint shape: round cylinder · square PETG box · pillow wave bag. The vessel drawing changes with it.
• Preset size seeds dimensions (you can override anything).
• Fill fraction: 0.05 – 1.0 of the straight section.
• Geometry (round): inner diameter T 0.02–3.0 m, straight height Ht 0.03–4.0 m, optional lock of H/T ratio 0.5–3.0.
• Geometry (square): side S 0.02–2.0 m, height Ht 0.03–4.0 m.
• Geometry (bag): width W 0.05–3.0 m, length L 0.05–4.0 m, height H 0.03–2.0 m.
• Bottom (round stirred only): flat / dished / conical. Dished depth ≈ 0.15·T, cone height ≈ 0.30·T by default.
• Baffles (round stirred only): toggle on/off; 2–8 baffles, width 0.04–0.15·T. Square bottles & bags are always flat-bottom and unbaffled.

Step 3 · Size — ONE method

Pick either "Type dimensions" or "Type target liquid litres" (e.g. 655 L). You never enter the same quantity twice.

• Dimensions mode: directly edit T/H (or S/H, or W×L×H).
• Litres mode: keep the footprint, solve Ht and fill so working volume == target. Range 0–5000 L.
• Working liquid volume also editable directly 0–5000 L (fills derived from a fixed Ht).

Step 4 · Liquid property

• Pick a fluid preset (water, PBS, CHO broth, glycerol, silicone oil, CMC, xanthan, kaolin slurry, blood, …) or toggle Custom liquid to type density 500–3000 kg/m³ and viscosity 0.01–1 000 000 mPa·s (≈ cP).
• Temperature 2–90 °C. Non-Newtonian presets (CMC, xanthan, blood) use shear-thinning / yield models.

Step 5 · Impeller

• Impeller count 1–4 on one shaft (round STR / mobile vessels). Bottles (square / DS) lock to a single stir bar.
• For each impeller: Type (see atlas below), diameter D 0.005 – 0.95·T, off-bottom clearance 0.002 – (h_liq − 0.005) m.
• Stir-plate coupling limit 0–300 mN·m (0 = auto by bar size): micro ≤20 mm → 8; lab 25–50 mm → 35; large 60–80 mm → 60; heavy-duty ≥80 mm → 120. Above the limit the bar slips / stalls.

Step 6 · Speed & process context

• Speed 5–3000 rpm (stirred & shaken).
• Shaken: orbit / shaking diameter 3–100 mm. Rocked: rock angle 1–12°, rate 5–45 rocks/min.
• Process context (guideline bands): mammalian CHO/HEK, insect Sf9, plant cell, microbial E. coli/yeast, filamentous fungi. Drives P/V and tip-speed warnings.
• Optional expanders (stirred): Gas sparge & mass transfer (vvm 0.005–3.0, O₂ 5–100 %), Heat transfer (ΔT 1–80 K, utility h 100–8000 W/m²K), Solids suspension (ρ 900–5000 kg/m³, d 1–5000 µm, x 0.01–40 %), Sampling probe (shear exposure at r, z).

4Blade-type atlas (23 impellers)

Every impeller is characterised by its turbulent power number Np∞, laminar asymptote Kp (Np·Re limit), primary flow number Fl, and Metzner–Otto shear constant ks. The family cards below use clean 3D product-style renders for realism; the close-clearance family uses a schematic because anchor/ribbon geometry is clearer drawn than rendered.

RADIAL

Radial-flow turbines — discharge straight out, then split up & down

Blades sit on a disc and throw liquid radially outward, creating two circulation loops (up the wall, down the centre, or vice-versa). Highest shear at the blade tips — great for gas dispersion, harsher on shear-sensitive cells.

• Rushton DT-6 — the classic 6-blade disc turbine, Np≈5.0 (Bates et al. 1963).
• CD-6 / BT-6 / Scaba 6SRGT — concave / hollow blades; better gas handling and kLa efficiency at lower Np.
• Flat paddle (2-blade) — large-D/T, common in glass vessels & DS bottles.

MIXED

Mixed-flow — pitched blades, mostly downward axial with radial component

Pitched-blade turbines (PBT) blend axial and radial flow. 4×45° and 6×45° are axial-dominant workhorses for blending and moderate gas handling. Magnetic stir bars (egg, cylindrical, octagonal, cross, floating, pivot-ring) are up-pumping mixed-flow devices for bottles and shake-style vessels.

• PBT 4×45°: Np∞ 1.60; PBT 6×45°: Np∞ 1.85.
• Stir bars: Np∞ 0.70–1.15; cross strongest, floating weakest. Effective hydraulic D ≈ 0.7× bar length.

AXIAL

Axial-flow hydrofoils & propellers — strong top-to-bottom pumping, low shear

High-efficiency, low-power-number blades that push liquid axially (top-to-bottom), giving excellent bulk blending and gentle shear — ideal for cell cultures. Propellers and low-pitch PBTs also fall here.

• A310 / HE-3 hydrofoils: Np∞ ≈ 0.30 — the efficiency champions.
• Maxflo WSE: up-pumping, Np∞ 0.48.
• Marine propellers (pitch 1.0 / 1.5): Np∞ 0.32 / 0.55.
• PBT 4×30°: Np∞ 0.95, more axial than the 45° version.

DISPERSER

Sawtooth (Cowles) disperser — extreme local shear for emulsification & deagglomeration

A toothed disc that generates intense localized dissipation for dispersing solids into liquids and making fine emulsions. Very low flow number, very high local shear — not for bulk blending.

• Cowles sawtooth: Np∞ 0.17, Kp 145, Fl 0.22, ks 14.

Full impeller data table

Np∞ = turbulent power number at standard D/T=1/3, w/D=1/5. Kp = laminar Np·Re asymptote. Fl = primary flow number. ks = Metzner–Otto average shear-rate constant. All are editable in the app's Advanced panel.

5Vessel preset library

Presets seed the geometry; everything stays editable. "Deq" is the area-equivalent diameter used by the correlations (square PETG bottles and wave bags are screened on Deq).

6Liquid / fluid presets

Pick a category then a fluid, or toggle Custom liquid to type density & viscosity directly. Non-Newtonian presets use shear-thinning (power-law) or yield-stress models.

Process-context guideline bands

Selecting a context adds P/V and tip-speed warning bands in the Overview:

7Reading the results

After ▶ Run, a horizontal tab bar appears (stirred mode shows all nine; shaken/rocked show Overview only). A red verdict in Overview links you straight to the tab that fixes the problem.

8Worked example — 1000 L CHO fed-batch fermenter

9Model limitations & best practice