Development and Design of a Two-Stage Contraction Zone and Test Section of an Organic Rankine Cycle Wind Tunnel

This contribution presents the development and design of a two-stage contraction zone and modular test section for a closed loop Organic Rankine Cycle (ORC) wind tunnel. The first contraction consists of four truncated cones, whose length and angle of inclination are derived from a two-stage optimization procedure, with the objective to minimize flow deviation and to avoid boundary-layer separation. The geometrical optimization yields a profile with minor deviation to the ideal polynomial shape, whereas the flow optimized shape minimizes flow separation at the break-points between the single conical pieces. The second contraction has to perform two major tasks, namely the acceleration of the flow up to a Mach number of Ma = 0.8 for organic fluids and the transformation of the circular inlet to a rectangular outlet cross-sectional shape, required by the working section. The circular-to-rectangular transition is accomplished by variation of the generalized ellipse, also known as Lamé curve. Smooth polynomials are then used to define the reduction of cross-sectional area. A comprehensive number of contraction geometries with fixed contraction ratio, variable length, and different points of inflection are analyzed with regards to minimum flow deviation, the avoidance of flow separation, as well as a uniform velocity field at the contraction outlet. A semi-analytical approach based on a potential flow solution in combination with the Stratford criterion is the basis for evaluating boundary-layer separation. The design of a two-part modular diffuser, based on the concept of a dumped diffuser, as commonly encountered in gas turbine design, is presented. The numerical results are compared with analytical findings and special characteristics of the different designs are explained. Finally, the overall design concept of the test section is presented.

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Unsteady Operation of a Highly Supersonic Organic Rankine Cycle Turbine

Journal of Turbomachinery ◽

10.1115/1.4033973 ◽

2016 ◽

Vol 138 (12) ◽

Cited By ~ 12

Author(s):

Enrico Rinaldi ◽

Rene Pecnik ◽

Piero Colonna

Keyword(s):

Boundary Layer ◽

Organic Rankine Cycle ◽

Suction Side ◽

Rankine Cycle ◽

Boundary Layer Separation ◽

Expansion Ratio ◽

Ideal Gas ◽

Rotor Blades ◽

Navier Stokes ◽

Shock Interactions

Organic Rankine cycle (ORC) turbogenerators are the most viable option to convert sustainable energy sources in the low-to-medium power output range (from tens of kWe to several MWe). The design of efficient ORC turbines is particularly challenging due to their inherent unsteady nature (high expansion ratios and low speed of sound of organic compounds) and to the fact that the expansion encompasses thermodynamic states in the dense vapor region, where the ideal gas assumption does not hold. This work investigates the unsteady nonideal fluid dynamics and performance of a high expansion ratio ORC turbine by means of detailed Reynolds-averaged Navier–Stokes (RANS) simulations. The complex shock interactions resulting from the supersonic flow (M ≈ 2.8 at the vanes exit) are related to the blade loading, which can fluctuate up to 60% of the time-averaged value. A detailed loss analysis shows that shock-induced boundary layer separation on the suction side of the rotor blades is responsible for most of the losses in the rotor, and that further significant contributions are given by the boundary layer in the diverging part of the stator and by trailing edge losses. Efficiency loss due to unsteady interactions is quantified in 1.4% in absolute percentage points at design rotational speed. Thermophysical properties are found to feature large variations due to temperature even after the strong expansion in the nozzle vanes, thus supporting the use of accurate fluid models in the whole turbine stage.

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Analysis of the Effect of Vortex Generator Spacing on Boundary Layer Flow Separation Control

Applied Sciences ◽

10.3390/app9245495 ◽

2019 ◽

Vol 9 (24) ◽

pp. 5495 ◽

Cited By ~ 4

Author(s):

Xin-kai Li ◽

Wei Liu ◽

Ting-jun Zhang ◽

Pei-ming Wang ◽

Xiao-dong Wang

Keyword(s):

Boundary Layer ◽

Wind Tunnel ◽

Kinetic Energy ◽

Flow Control ◽

Flow Separation ◽

Lift Coefficient ◽

Boundary Layer Separation ◽

Wind Tunnel Experiments ◽

Flow Separation Control ◽

Layer Separation

During the operation of wind turbines, flow separation appears at the blade roots, which reduces the aerodynamic efficiency of the wind turbine. In order to effectively apply vortex generators (VGs) to blade flow control, the effect of the VG spacing (λ) on flow control is studied via numerical calculations and wind tunnel experiments. First, the large eddy simulation (LES) method was used to calculate the flow separation in the boundary layer of a flat plate under an adverse pressure gradient. The large-scale coherent structure of the boundary layer separation and its evolution process in the turbulent flow field were analyzed, and the effect of different VG spacings on suppressing the boundary layer separation were compared based on the distance between vortex cores, the fluid kinetic energy in the boundary layer, and the pressure loss coefficient. Then, the DU93-W-210 airfoil was taken as the research object, and wind tunnel experiments were performed to study the effect of the VG spacing on the lift–drag characteristics of the airfoil. It was found that when the VG spacing was λ/H = 5 (H represents the VG’s height), the distance between vortex cores and the vortex core radius were approximately equal, which was more beneficial for flow control. The fluid kinetic energy in the boundary layer was basically inversely proportional to the VG spacing. However, if the spacing was too small, the vortex was further away from the wall, which was not conducive to flow control. The wind tunnel experimental results demonstrated that the stall angle-of-attack (AoA) of the airfoil with the VGs increased by 10° compared to that of the airfoil without VGs. When the VG spacing was λ/H = 5, the maximum lift coefficient of the airfoil with VGs increased by 48.77% compared to that of the airfoil without VGs, the drag coefficient decreased by 83.28%, and the lift-to-drag ratio increased by 821.86%.

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Simulations of the Atmospheric Boundary Layer in a Wind Tunnel with Short Test Section

Journal of Aerospace Technology and Management ◽

10.5028/jatm.v5i3.190 ◽

2013 ◽

Vol 5 (3) ◽

pp. 305-314 ◽

Cited By ~ 2

Author(s):

Luciana Bassi Marinho Pires ◽

Igor Braga De Paula ◽

Gilberto Fisch ◽

Ralf Gielow ◽

Roberto Da Mota Girardi

Keyword(s):

Boundary Layer ◽

Wind Tunnel ◽

Atmospheric Boundary Layer ◽

Test Section ◽

Short Test

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Numerical Study of Wall Influence on Boundary-Layer Transition for Two-Dimensional NACA 16-012 and 4412 Hydrofoil Sections

Journal of Ship Research ◽

10.5957/jsr.1990.34.1.38 ◽

1990 ◽

Vol 34 (01) ◽

pp. 38-47

Author(s):

R. Latorre ◽

R. Baubeau

Keyword(s):

Boundary Layer ◽

Test Section ◽

Numerical Study ◽

Suction Side ◽

Boundary Layer Separation ◽

Boundary Layer Transition ◽

Layer Transition ◽

Turbulent Separation ◽

Side Pressure ◽

Effective Angle

One of the difficulties in hydrofoil model tests is the relatively low Reynolds number of the test piece and the presence of the test section walls. This paper presents the results of systematic calculations of the potential flow field of NA 4412 and NACA 16-012 hydrofoil in a test section with wall-to-chord ratios h/c -1.0. The corresponding boundary-layer calculations using the CERT calculation scheme are presented to show the influence of the nearby walls on shifting the location of the boundary-layer laminar-turbulent separation as well as turbulent separation. By introducing an effective angle of attack, it is possible to obtain close agreement in the calculated and measured suction side pressure distortion as well as the locations of the boundary-layer separation and transition.

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