In this paper, the optimization is carried out for a synthetic jet based piezoelectric air pump. The structural parameters which affect the output flowrate are determined and orthogonal test method is used to find out the optimal values of these parameters. Driven by a 150 Vpp, 3.15 kHz sinusoidal voltage signal, the optimized pump reaches its maximum output flowrate of 2.79 L/min, which is 32.9% higher than that before optimization. Using the synthetic jet based piezoelectric air pump as gas source, an open-loop detection and closed-loop control system is built for electronic cooling. The open-loop experiments show that the heater’s surface temperature can be maintained at around 97.9 °C when the cooling distance is 60 mm, which is 32.5% lower than the initial value. The closed-loop control system can limit the temperature within the set interval. Both the open and closed-loop system show that the synthetic jet based piezoelectric air pump has application prospects in the field of electronic cooling.

Optimization of a synthetic jet based piezoelectric air pump and its application in electronic cooling

This paper presents the results of experimental investigations of 108 geometrical configurations of a loudspeaker-driven synthetic jet (SJ) actuator. The considered cases of the SJ actuator were characterized by a high coupling ratio. The experiment was performed to determine the impact of geometry on the Helmholtz resonance frequency. Geometrical parameters of the orifice diameter, orifice length, and cavity volume were changed within a wide range. The dependences of electrical and flow parameters that characterized the synthetic jet actuators as a function of the excitation frequency were also identified. The main goal of the research was to identify the optimal mathematical formula of the model to calculate the Helmholtz resonance frequency in the case of synthetic jet actuators. To determine the model that was characterized by the best fit of the experimental results, an additional geometrical dimensionless parameter, representing the ratio of the orifice cross-section area to the cross-section area of the cavity, was introduced. A significant impact of this parameter on the effective orifice length was noted. Based on the research findings, a model was obtained for which the results of the experiment were in the error range of ±6% for 95% of the measurement data. The obtained model is an improved version of the classical model used in the description of the resonance frequency in the case of a synthetic jet actuator. The model enables highly accurate determination of the Helmholtz resonance frequency at which the maximum synthetic jet actuator parameters occur.

Helmholtz Resonance Frequency of the Synthetic Jet Actuator

In this paper, an accurate model to simulate the dynamics of the flow of synthetic jets (SJ) in quiescent flow is proposed. Computational modeling is an effective approach to understand the physics involved in these devices, commonly used in active flow control for several reasons. For example, SJ actuators are small; hence, it is difficult to experimentally measure pressure changes within the cavity. Although computational modeling is an advantageous approach, experiments are still the main technique employed in the study of SJs due to the lack of accurate computational models. The same aspect that represents an advantage over other techniques also represents a challenge for the computational simulations, such as capturing the unsteady phenomena, localized compressible effects, and boundary layer formation characteristic of this complex flow. One of the main challenges in the simulation of SJs is related to the fact that the spatial and temporal scales of the actuator and the corresponding flow control application differed in several orders of magnitude. Hence, in this study we focus on the use of Computational Fluid Dynamics (CFD) and Reduced Order Models (ROM) to develop an accurate yet low-cost model to capture the complexities of the flow of a SJ in quiescent flow. Numerical results show two possible paths for SJ modeling; (1) to obtain a boundary condition to predict velocity profile and jet formation from experimental data of diaphragm’s deformation; and, (2) to predict peak velocity at the jet’s outlet with a ROM approach and to use the physical details of the actuator to develop an accurate boundary condition for CFD. Both approaches are validated through experimental data available in the literature; good agreement between results from CFD, Lumped Element Model (LEM), and experimental data are achieved. Finally, it was concluded that the coupling between LEM and CFD is a novel and accurate approach, which improves CFD due to the advantages of LEM closing the gap between LEM’s lack of flow detail and CFD’s lack of geometrical/physical information of the actuator.

https://www.mdpi.com/1996-1073/13/24/6514/pdf

Towards Accurate Boundary Conditions for CFD Models of Synthetic Jets in Quiescent Flow

Synthetic jet actuators are an alternative to traditional impinging jets with many benefits. However due to the complex flow physics involved, they require active control via a reduced order model if the jet operating conditions are to be set reliably. An anomaly in the cavity pressure time trace has been identified for a certain operating condition, which has not been investigated by previous literature. A better understanding of the physics involved could help improve reduced order models. A facility has been built that can reproduce the anomaly and collect other data normally used in reduced order models. This additional data includes cavity pressure, diaphragm displacement, and velocity fields using particle image velocimetry.

An Investigation into a Pressure Anomaly during Synthetic Jet Operation

The authors wish to make the following corrections to this paper [...]

https://www.mdpi.com/2076-0825/8/1/16/pdf

Correction: Persoons, T.; Cressall, R.; Alimohammadi, S. Validating a Reduced-Order Model for Synthetic Jet Actuators Using CFD and Experimental Data. Actuators 2018, 7, 67

Synthetic jet actuators (SJA) are emerging in various engineering applications, from flow separation and noise control in aviation to thermal management of electronics. A SJA oscillates a flexible membrane inside a cavity connected to a nozzle producing vortices. A complex interaction between the cavity pressure field and the driving electronics can make it difficult to predict performance. A reduced-order model (ROM) has been developed to predict the performance of SJAs. This paper applies this model to a canonical configuration with applications in flow control and electronics cooling, consisting of a single SJA with a rectangular orifice, emanating perpendicular to the surface. The practical implementation of the ROM to estimate the relationship between cavity pressure and jet velocity, jet velocity and diaphragm deflection and applied driving voltage is explained in detail. Unsteady Reynolds-averaged Navier Stokes computational fluid dynamics (CFD) simulations are used to assess the reliability of the reduced-order model. The CFD model itself has been validated with experimental measurements. The effect of orifice aspect ratio on the ROM parameters has been discussed. Findings indicate that the ROM is capable of predicting the SJA performance for a wide range of operating conditions (in terms of frequency and amplitude).

/pdf/validating-a-reduced-order-model-for-synthetic-jet-actuators-2j6ztr6uww.pdf

Rick Cressall

Papers

Validating a Reduced-Order Model for Synthetic Jet Actuators Using CFD and Experimental Data

An Investigation into a Pressure Anomaly during Synthetic Jet Operation

Correction: Persoons, T.; Cressall, R.; Alimohammadi, S. Validating a Reduced-Order Model for Synthetic Jet Actuators Using CFD and Experimental Data. Actuators 2018, 7, 67