Effect of manhole molds and inlet alignment on the hydraulics of circular manhole at changing surcharge

Head loss coefficient of a manhole is dependent on various hydraulic and structural characteristics. This study analyses the effect on manhole head loss coefficients using numerical VOF model due to three factors: manhole structural mold shapes, small changes in inlet orientations and changes in the manhole to inlet pipe ratios. Head loss coefficients showed a strong dependence on the available surcharge. Presence of sump created the maximum head loss while benching provided the best efficiency. Within small deviation of inlet pipe orientations, two different hydraulic regimes were observed indicating effects on both head loss coefficients and threshold surcharge heights. Change of manhole to inlet pipe diameter ratios (Φ_m/Φ_p) showed three head loss characteristics. Head loss in small manholes (Φ_m/Φ_p<3) did not change with surcharge. Medium manholes (3 < Φ_m/Φ_p< 4.0) showed high head losses up to a specific surcharge. Big manholes (Φ_m/Φ_p>4.5) showed a high head loss at all the surcharges.