**2. Materials and methods**

## **2.1 Test rig**

The centrifugal pump under study, hereafter referred to as PAT, is an ITT Goulds of 1491.4 W (2 HP), with the specifications shown in **Table 2**.

The PAT was instrumented with pressure transducers in the high- and lowpressure orifices; two pressure fluctuation sensors on the volute; a torque sensor and an encoder on the shaft; a flow meter in the high-pressure pipe; and a frequency drive. The PAT was added to the test rig, which consisted of a closed pipe loop, a supply tank, and a recirculation pump, which was used to simulate the hydraulic head conditions for the PAT.

The pressure fluctuation sensors were placed on the volute in the same vertical plane, where sensor 1 (DYT1) and sensor 2 (DYT2) are 135° apart, as shown in **Figure 1**. The circular arrow inside the circle represents the direction of flow in the pump working as a turbine.

All sensor signals were acquired simultaneously by a National Instruments® CompaqRio® 9045 data acquisition unit. The signals from the pressure fluctuation, torque, and encoder sensors were acquired at a rate of 102.4 k samples/s. Signals from the pressure transducers and flow meter were acquired at 50 k samples/s.

#### **Figure 1.**

*Diagram of the location of the pressure fluctuation sensors on the volute.*


#### **Table 2.**

*Geometric characteristics of the PAT.*
