Leveraging Throughflow Results to Understand Hydraulic Behavior Across Varying Flow Rates
Designing hydraulic turbomachinery—such as centrifugal pumps, fans, or water turbines—involves balancing a wide range of input variables. Designers must define operating conditions like flow rate, rotational speed, impeller geometry, number of vanes, and specific energy (or head), all of which are interconnected and significantly affect performance. This complex design space can be overwhelming, especially when one seeks to optimize hydraulic efficiency, power consumption, or torque while avoiding cavitation or performance drops at off-design conditions.
Even with a well-established target, such as achieving a certain head or power, determining whether the selected combination of design parameters is optimal isn't always straightforward. Designers often rely on experience or empirical formulas, which, while useful, might not capture the full picture—especially for novel or constrained applications. This uncertainty can lead to suboptimal configurations that underperform or require extensive redesign.
Designing efficient turbomachinery requires tools that are both fast and reliable, especially in the early stages of development. Vista TF (Throughflow), part of the ANSYS Workbench suite, is a streamline-curvature solver designed to evaluate radial blade rows—such as those found in centrifugal pumps, radial compressors, and turbines—using a quasi-1D approach.
While it doesn’t offer the full detail of 3D CFD, Throughflow enables rapid parametric studies of impeller geometries and operating points. Its simplified yet physically-informed modeling allows engineers to quickly assess a wide range of configurations—providing immediate feedback on critical performance indicators such as head, torque, and efficiency (both stage and isentropic).
To address the challenges of navigating complex design spaces, Throughflow offers an efficient way to evaluate performance trends based on 1D flow calculations. By varying parameters like mass flow rate or blade geometry, designers can gain insight into how these inputs affect hydraulic behavior. This makes Throughflow an excellent tool for early-stage screening and iterative refinement, helping engineers focus expensive 3D CFD efforts on only the most promising candidates.
Methods
The setup process begins within the ANSYS Workbench environment by dragging and dropping the Vista CPD module, which is used for basic centrifugal pump sizing. In the first step, the user provides the required design point, including inputs such as flow rate, head, rotational speed, and fluid properties. Based on these conditions, Vista CPD generates a preliminary impeller geometry and estimates key performance parameters.
A unique feature of Vista CPD is that it produces efficiency curves as a function of the specific speed (Ωs) and the specific diameter ratio (Q/N). These non-dimensional parameters generalize the performance characteristics of the impeller:
Therefore, Vista CPD offers theoretical efficiency maps based on dimensionless coefficients like the flow coefficient and specific speed. While useful for general guidance, these maps rely on empirical trends and are not tied to a specific geometry. To evaluate a real impeller design more accurately, Throughflow provides a quasi-1D analysis based on actual blade geometry and input conditions. This allows for a more reliable assessment of performance metrics—such as head and efficiency—across i.e., a range of flow rates.
Results
In the first step of the process, initial design inputs are defined within Vista CPD, as shown in the figure below. These inputs include the operating conditions—most notably the mass flow rate—as well as the main geometric features of the impeller. Key parameters involve the hub and shroud contours, the shape and positioning of the leading and trailing edges, the number of blades, and other dimensions critical to the impeller’s baseline design. This configuration defines a single design point, which is then used as the starting geometry for subsequent performance evaluation.
Then, the design is transferred to a new Throughflow module, where the solver runs automatically and completes within a few minutes. Once the calculation finishes, the user can access the results cell to visualize key performance outputs. At this stage, contour plots become available, providing insight into the flow behavior through the impeller channels, as well as variables such as velocity, pressure, and blade loading.
Note that the contour of pressure suggests a gradual distribution except in the highlighted region. Moreover, the meridional velocity (Cm) shows a significant increase near the leading edge, particularly close to the hub. This suggests that the inlet geometry or the rotational speed may be causing the flow to contract and accelerate prematurely. Such a pattern indicates a non-uniform distribution of the incoming flow.
While this behavior is not necessarily problematic, it highlights a critical region of the impeller where flow imbalance could eventually lead to inefficiencies or flow separation in a full 3D simulation. Identifying this early using Throughflow provides valuable insight for refining the inlet geometry and guiding further parametric analysis. Therefore, we can also perform a parametric analysis using the mass flow rate as the input parameter and different efficiencies as the outlet parameters.
Watch the full video walkthrough to see how to setup the model and check results to accelerate early-stage pump design and reveal key performance trends.
CFD modeling demonstrates its potential to optimize and evaluate hydraulic structures through Ansys's advanced solutions. For preprocessing, Ansys SpaceClaim and Discovery Modeling facilitate CAD creation and preparation, while Ansys Fluent and CFX tackle various simulation challenges. High-fidelity postprocessing tools, like Ansys Ensight, effectively analyze and visualize large datasets.
Additionally, CFD results can be integrated with structural analyses in Fluid-Structure Interaction (FSI) scenarios, supported by Ansys Mechanical and LS-Dyna. Techniques such as Design of Experiments (DOE) and advanced optimization are facilitated by DesignXplorer and Ansys OptiSlang within the Workbench platform. Ansys also provides HPC licenses and GPU capabilities for parallel processing of complex models, ensuring thorough evaluations.
Ozen Engineering Inc. leverages its extensive consulting expertise in CFD, FEA, optics, photonics, and electromagnetic simulations to achieve exceptional results across various engineering projects, addressing complex challenges like multiphase flows, erosion modeling, and channel flows using Ansys software.
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