Numerical and Experimental Investigation of Trailing Edge - PowerPoint PPT Presentation

Numerical and Experimental Investigation of Trailing Edge Modifications of Centrifugal Wastewater Pump Impellers Oliver Litfin a Antonio Delgado a Kais Haddad b Horst Klein b a University of Erlangen-Nuremberg, Institute of Fluid Mechanics b Sulzer Pump Solutions Germany GmbH ASME 2017 Fluids Engineering Division Summer Meeting, July 31 - August 3, 2017, Waikoloa, Hawai’i, USA E r l a n g e n

Scope of the work E r l a n g e n

E r l a n g e n Scope of this work In classical textbooks (Guelich, Karassik) it is stated, that under-filing typically leads to an increase of 3 percent in head while pump efficiency stays constant or increases slightly by 0.5 to 1 percent. More recent publications (Wu et al. 2015, Gao et al. 2016) showed significant increase in pump efficiency for a mixed-flow and a low-speed centrifugal pump due to trailing edge modifications. In this work the effect of trailing edge modifications on the performance of the wastewater pump impellers is numerically investigated. ⇒ Can under-filing increase the efficiency of a wastewater pump impeller? ⇒ How can under-filing increase the hydraulic efficiency? ⇒ What are the main mechanisms involved? Oliver Litfin a , Antonio Delgado a , Kais Haddad b , Horst Klein b FEDSM 2017 | | FAU | 3

Description of the test pumps E r l a n g e n

E r l a n g e n Wastewater pumps NS065 and NS100 Property NS065 NS100 D 2 0.38 m 0.48 m D 1 t / D 2 0.47 0.53 b 2 / D 2 0.25 0.26 β 2 b @camber 29.0 degree 18.4 degree s θ 2 / D 2 0.06 0.12 N s (US units) 1780 2730 default (cut-off) straight-cut under-filed (incl. blunt portion) Oliver Litfin a , Antonio Delgado a , Kais Haddad b , Horst Klein b FEDSM 2017 | | FAU | 5

E r l a n g e n Numerical model � CFX � 17.1) • 3D RANS (ANSYS R R • Impeller only in rotating frame • No tip-gap, no backchannel • k - ω -SST turbulence model with curvature correction • 1st to 2nd order upwind blending scheme with β = 0.95 • Unstructured mesh with 2.8 million nodes (tetra and prism elements) • Average y+ ≈ 0.5 • Convergence criteria 10 -5 for rms residuals of the mass and momentum equations Oliver Litfin a , Antonio Delgado a , Kais Haddad b , Horst Klein b FEDSM 2017 | | FAU | 6

E r l a n g e n Dimensionless characteristics for both impellers (CFD) NS065 NS100 0.18 1.05 0.14 1.05 0.16 1 0.12 1 0.14 0.95 0.1 0.95 0.12 0.9 0.08 0.9 η * η * Ψ Ψ 0.1 0.85 0.06 0.85 NS065 Ψ NS100 Ψ NS065 η * NS100 η * 0.08 0.8 0.04 0.8 NS065SC Ψ NS100SC Ψ NS065SC η * NS100SC η * NS065UF Ψ NS100UF Ψ 0.06 0.75 0.02 0.75 NS065UF η * NS100UF η * 0.04 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.015 0.02 0.025 0.03 0.035 0.04 Φ Φ 2 ) ; Ψ = ( g · H ) / ( ω · D 2 ) 2 ; η ∗ = η/η max , ref • Φ = Q / ( ω · D 3 • Both trailing edge modifications increase the head coefficient • Under-filing leads to an increased efficiency for the NS100 impeller, for the NS065 impeller efficiency is the same as with default trailing edge Oliver Litfin a , Antonio Delgado a , Kais Haddad b , Horst Klein b FEDSM 2017 | | FAU | 7

Loss analysis based on rothalpy E r l a n g e n

E r l a n g e n Concept of rothalpy and stations for evaluation Outlet h T = h + 0 . 5 · C 2 − U · C θ 2b 2b 2 TE 2 p T = p + 0 . 5 · ρ · C 2 − ρ · U · C θ 2a 2a PA 1 p T = p 0 − ρ · U · C θ 0 LE 1b 1a • If rothalpy is constant along a streamline (isentropic) → rise in stagnation pressure must correspond to the change in angular momentum. • Impeller was divided in three sections by defining a couple of stations in the flowpath • Leading edge section (LE), passage section (PA) and trailing edge section (TE) • Rothalpy losses were evaluated for the LE, PA and TE section separately Oliver Litfin a , Antonio Delgado a , Kais Haddad b , Horst Klein b FEDSM 2017 | | FAU | 9

E r l a n g e n Impeller section rothalpy pressure losses (normalized) NS065 NS100 0 0 -0.005 -0.005 -0.01 dp T / 0.5* ρ *U2 2 dp T / 0.5* ρ *U2 2 -0.01 -0.015 -0.015 -0.02 -0.02 -0.025 NS065, LE NS100, LE -0.025 -0.03 NS065, PA NS100, PA NS065, TE NS100, TE -0.035 -0.03 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.015 0.02 0.025 0.03 0.035 0.04 Φ Φ • For NS065 at BEP ( Φ =0.02) LE and TE losses are almost equal ( ≈ -0.004). PA losses are around -0.01. • For NS100 similar behavior except LE losses → slightly misaligned flow at BEP . Oliver Litfin a , Antonio Delgado a , Kais Haddad b , Horst Klein b FEDSM 2017 | | FAU | 10

E r l a n g e n Rothalpy pressure losses at LE for different TE shapes NS065 NS100 0 0 -0.005 -0.01 -0.01 dp T,LE / 0.5* ρ *U2 2 dp T,LE / 0.5* ρ *U2 2 dp T,LE / dp t,is dp T,LE / dp t,is -0.02 -0.015 0 -0.02 0 -0.03 -0.01 -0.01 -0.02 NS065 NS100 -0.02 NS065SC NS100SC -0.03 NS065UF NS100UF -0.04 -0.03 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.015 0.02 0.025 0.03 0.035 0.04 Φ Φ • Normalized rothalpy pressure losses (bottom half) not affected by TE (quite obvious). • Relative rothalpy pressure losses (top half) are affected by TE shape. This is due to the increased work input (higher Ψ -values). Oliver Litfin a , Antonio Delgado a , Kais Haddad b , Horst Klein b FEDSM 2017 | | FAU | 11

E r l a n g e n Rothalpy pressure losses at PA for different TE shapes NS065 NS100 0 0 -0.01 -0.03 -0.02 dp T,PA / 0.5* ρ *U2 2 dp T,PA / 0.5* ρ *U2 2 dp T,PA / dp t,is dp T,PA / dp t,is -0.06 -0.03 0 -0.04 -0.01 -0.09 -0.01 -0.02 -0.02 NS065 NS100 NS065SC NS100SC -0.03 -0.03 NS065UF NS100UF -0.04 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.015 0.02 0.025 0.03 0.035 0.04 Φ Φ • For NS065 impeller normalized rothalpy pressure losses are not affected by TE shape. Relative losses are reduced at higher flow coefficients due to the TE modifications. • For NS100 impeller normalized losses are also affected by TE shape. Relative losses are strongly reduced by under-filing at all flow coefficients. Oliver Litfin a , Antonio Delgado a , Kais Haddad b , Horst Klein b FEDSM 2017 | | FAU | 12

E r l a n g e n Rothalpy pressure losses at TE for different TE shapes NS065 NS100 0 0 -0.01 -0.03 -0.02 dp T,TE / 0.5* ρ *U2 2 dp T,TE / 0.5* ρ *U2 2 dp T,TE / dp t,is dp T,TE / dp t,is -0.06 -0.03 0 -0.04 0 -0.09 -0.01 -0.02 -0.02 NS065 NS100 -0.04 NS065SC NS100SC -0.03 NS065UF NS100UF -0.04 -0.06 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.015 0.02 0.025 0.03 0.035 0.04 Φ Φ • Normalized losses are strongly increased by straight-cut TE → large mixing losses. Default and under-filed TE are very similar for NS065. For NS100 under-filed TE reduces losses at higher flow coefficients. • For NS100 there is a strong decrease in relative losses for under-filed TE at higher flow coefficients. Oliver Litfin a , Antonio Delgado a , Kais Haddad b , Horst Klein b FEDSM 2017 | | FAU | 13

Effect of TE shape on slip factor E r l a n g e n

E r l a n g e n CFD slip factor for different TE shapes NS065 NS100 0.8 0.75 0.75 0.7 0.7 0.65 � CFD � CFD 0.65 0.6 0.6 0.55 NS065 NS100 0.55 NS065SC 0.5 NS100SC NS065UF NS100UF 0.5 0.45 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.015 0.02 0.025 0.03 0.035 0.04 � � • σ CFD = 1 − ∆ C θ 2 with ∆ C θ 2 = C θ 2 , th − C θ 2 U 2 • NS065 σ ≈ 0 . 6 @BEP , NS100 σ ≈ 0 . 55 @BEP • Slip factor increased by TE modifications compared to default TE. Oliver Litfin a , Antonio Delgado a , Kais Haddad b , Horst Klein b FEDSM 2017 | | FAU | 15

E r l a n g e n CFD slip factor: Trailing edge flow NS065 0.8 0.75 0.7 � CFD 0.65 0.6 NS065 0.55 NS065SC NS065UF 0.5 0.005 0.01 0.015 0.02 0.025 0.03 0.035 � • Flow deflection towards the circumferential direction for default TE (top). • With both TE modifications the flow detached at the trailing edge end of the pressure side → less flow deflection, increased slip factor. Oliver Litfin a , Antonio Delgado a , Kais Haddad b , Horst Klein b FEDSM 2017 | | FAU | 16

Experimental validation E r l a n g e n

E r l a n g e n Experimental results (whole pump) NS065 NS100 0.18 1.1 0.14 1.1 0.17 1 0.13 1 0.16 0.9 0.12 0.9 0.15 0.8 0.11 0.8 0.14 0.7 0.1 0.7 0.13 0.6 0.09 0.6 η * η * Ψ Ψ 0.12 0.5 0.08 0.5 0.11 0.4 0.07 0.4 0.1 0.3 0.06 0.3 NS065 Ψ NS100 Ψ NS065 η * NS100 η * 0.09 0.2 0.05 0.2 NS065UF Ψ NS100UF Ψ 0.08 0.1 0.04 0.1 NS065UF η * NS100UF η * 0.07 0.03 0 0.005 0.01 0.015 0.02 0.025 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 Φ Φ • For NS065 under-filing does increase the head coefficient by 7.7 percent @BEP , while efficiency remains constant. • For NS100 head coefficient @BEP is increased by even 11.7 percent while efficiency is increased by 1.7 percent. The maximum efficiency is even increased by 4.5 percent, shifted to higher flow coefficient. Oliver Litfin a , Antonio Delgado a , Kais Haddad b , Horst Klein b FEDSM 2017 | | FAU | 18

Conclusions E r l a n g e n