A new swirl apparatus: design, numerical analysis and preliminary measurements

Transcription

1 A new swirl apparatus: design, numerical analysis and preliminary measurements Romeo Susan-Resiga, Professor, PhD Sebastian Muntean, Senior Researcher, PhD Constantin Popescu, PhD student Daniel Mos, Master student Raul Szakal, Master student Research Centre for Complex Fluid Systems Engineering IAHRWG 2017

2 Why a new swirl apparatus? h$p://qnet-erco0ac.cfms.org.uk/ w/index.php/ac6-14 The swirl apparatus developed for the past decade at the Politehnica University Timișoara is available as an ERCOFTAC test case (detailed geometry, experimental data). It was extensively used for precessing vortex rope invesrgarons. A new, simpler and more controlable configuraron is suitable for basic swirling flow stability studies Our aim is to develop and validate mathemarcal models and tractable algorithms for predicrng the instabilires in swirling flows without brute force 3D unsteady turbulent flow computarons. 2

3 Design of the meridian contour dimensionless radial coordinate We start with a converging pipe and we progress inwards with constant cross -secron area tubes dimensionless axial coordinate 3

4 Design of the meridian contour + bladed region radial coordinate [mm] bladed region mm mm blade ring swirling flow The convergent part of the pipe is manufactured separately as a profiled ring axial coordinate [mm] 4

5 Meridian cross-section of the swirl apparatus The swirl apparatus includes a bladed swirl generator (upstream) and a test secron (downstream) with oprcal windows for LDV measurements and pressure sensors. 5

6 Meridian cross-section of the swirl apparatus The blades are plane, leaned with respect to the meridian plane 6

7 Meridian cross-section of the swirl apparatus Flow rotaron is the result of the flow tangency condiron on the leaned blades. The convergent pipe generated inwards radial velocity, with a corresponding circumferenral velocity component. v θ v r = tanλ(r) tanλ(r) = r r 2 r 2 r := circle tangent to the blades λ := lean angle 7

8 Swirl apparatus installed on the test rig 8

9 Axisymmetric swirling flow model In the axisymmetric swirling flow model, the blades effect is represented by the blade blockage coefficient and the blade body force, respecrvely. This is the idea of the turbomachinery throughflow models. In our case we have 36 blades, thus the axisymmetric model is appropriate. (βρ) t (βρv) t + ( βρv) = 0, + ( βρvv) = β p + βρf B +viscous terms, where β(r) = 1 N δ B B tanλ(r) is the blade blockage, 2πr and f B is blade body force acceleration. 9

10 Axisymmetric swirling flow model The blade body force is normal to the blades, therefore there are only circumferenral and radial components. f B θ = v v r z z + v r f B r = f B θ tanλ. v r z v 2 r r tan2 λ tanλ, The blade body force is implemented as source terms in the radial and circumferenral momentum equarons, using User Defined FuncRons (UDF). For each cell we can access the cell centroid coordinates, as well as velocity Components and their gradients. 10

11 Velocity profiles measured and computed Upstream window Downstream window 6 6 velocity components [m/s] velocity components [m/s] radius [m] radius [m] The 2D axisymmetric swirling flow computarons, with blade body force and blade blockage, qualitarvely captures the swirling flow parrcularires: Axial velocity with a strong central wake Swirl velocity with a central rigid body rotaron 11

12 Preliminary conclusions ü The new swirl apparatus has a very simple geometry, with plane leaned blades ü Swirl is generated by a mild flow contracron -> radial velocity -> flow tangency -> circumferenral velocity ü The swirl generator is separated from the test secron -> allows for flexibility in test secron geometry: cylindrical pipe, step diffuser, conical diffuser, etc. ü A 2D axisymmetric swirling flow model can reasonably capture the axial and circumferenral velocity profiles. ü The Achilles heel of the 2D axisymmetric swirling flow computarons is the turbulence model (physically there is no such thing as axisymmetric turbulence) 12