Elastomer Surface Pressure Sensor and its Intergration to a 'Smart' surface for Active Flow Control

飞机表面与空气之间的无滑移状态不仅对阻力有影响，而且对升力也有影响。对以碳为基础的经济来说，一个明显的潜在巨大好处是飞机、公路车辆和船舶的燃料消耗减少。这样做的技术目标，连同许多其他的，构成了一个重要的研究领域，称为流动控制，同样的技术用于减少阻力，也可以用来帮助控制飞机，通过提高他们的稳定性和机动性，这是产生额外的升力或推力时需要的。这通常是通过延迟分离来实现的，也就是说，通过防止飞机在缓慢飞行或在接近其飞行包线极限时可能发生的失速。另一种方法是在提供推力的射流中引入微小的扰动，使其更快地偏转或破裂。如果飞机是无人驾驶的，这种控制将特别有用。我们希望在这里做的是利用聚合物材料的最新发展（最常用的聚合物是PVC或塑料），其中一些具有压电特性。通过压电，我们的意思是聚合物可以通过施加电压或电荷来膨胀或压缩，相应地，当聚合物被压缩时产生电荷。这些也被称为电活性聚合物或EAPS。如果这种聚合物具有正确的性质并经过优化设计，它可以用于许多应用，例如在人体中作为人造肌肉。显然，身体中最重要的“肌肉”是心脏，它当然参与了全身血液的流动。我们的具体应用是采用高尔夫球上的酒窝的想法，并将其用作执行器，作为改变任何类型物体周围边界层流动特性的基础。事实上，酒窝是非常有效的涡流发生器，我们已经开始使用由EAP制成的酒窝，这样酒窝就由一个膜片组成，它可以以循环（或谐波）的方式上下弹出，或者可以在需要的时候这样做，一个所谓的随需应变的涡流发生器。在这种情况下，我们希望酒窝产生一个已知强度的单一漩涡，时间长短随我们的意愿而定，这需要了解基本的流体行为，以便实现模型。这意味着我们必须感知边界层的性质，我们可以通过利用EAP的压电特性来做到这一点。然后，聚合物不仅具有用于控制边界层的凹窝阵列，而且还具有压力传感器阵列，以便可以使用表面压力信号来控制凹窝。我们甚至可以开发一种“智能全聚合物皮肤”，它由单独的EAP层组成，其中各个层可以专门设计用于感知皮肤的力，或者作为按需驱动的微窝驱动器。然后我们就能感知到表面的压力并在相同的位置启动。最初，我们希望仅通过开环控制来控制边界层。在这种情况下，测量的压力仅用于诊断酒窝的影响。然而，更复杂（而且可能更有益）的是闭环控制，其中测量的压力用于确定何时何地应启动凹窝。这将需要一个控制模型，这是我们希望流如何的清晰预期。每个模型都将非常依赖于许多条件，尤其是流的类型。

The no-slip condition between the surface of an aircraft and the air in which it flies is responsible not only for drag, but for the lift as well. An obvious potentially huge benefit to a carbon-based economy is the reduction in fuel consumption of aircraft, road vehicles and ships. The technological goal of doing this, together with many others, constitutes an important area of research called flow control and the same techniques used to reduce drag may also be used to help control aircraft by improving their stability and manoeuvrability, that is producing additional lift or thrust when it is needed. This is often done by delaying separation, that is, by preventing stall that could otherwise occur when an aircraft is flying slowly or when it is manoeuvring near the limits of its flight envelope. Another way of doing this could be by introducing small perturbations into the jet that provides the thrust so making it deflect or break up more quickly. Such control of an aircraft would be especially useful if it were unmanned. What we wish to do here is to take advantage of recent developments in materials called polymers (the most often used polymer is PVC or plastic) some of which possess piezoelectric properties. By piezoelectric, we mean that the polymer can be made to expand or compress by applying a voltage or charge, and correspondingly, produce charge when the polymer is compressed. These are also called electroactive polymers or EAPS. If the polymer has the right properties and is designed optimally, it can be used in a great many applications such as the in the body as an artificial muscle. Obviously the most important 'muscle' in the body is the heart which is of course involved in the flow of blood around the body.Our specific application is to take the idea of a dimple on a golf ball and use it as an actuator, as the basis of changing the properties of the boundary layer flow around more-or-less any type of body. Dimples are, in fact, very efficient vortex generators and we have started using dimples that are made of EAP so that the dimple consists of a diaphragm that pops up and down either in a cyclic (or harmonic) fashion, or can be made to do so when required, a so-called ondemand vortex generator. In this case, we would wish the dimple to produce a single vortex of known strength for as long or as short as we would wish, and this requires an understanding of the basic fluid behaviour so that a model may be implemented. This means we have to sense the properties of the boundary layer and we can do this by taking advantage of the piezoelectric behaviour of the EAP. Then the polymer not only has an array of dimples for controlling the boundary layer, but it also has an array of pressure sensors so that the surface pressure signal may used to control the dimples. We can even develop a 'smat all-polymer skin that is made up of separate EAP layers where individual layers can be designed specifically to sense the forces of the skin, or to be actuated as an on-demand dimple actuator. Then we would be able to sense the pressure on the surface and actuate at the same position. Initially, we hope to control boundary layer by open-loop control only. In this case, the measured pressure is only used to diagnose the effect of the dimples. However, much more complicated (and potentially much more beneficial) is closed-loop control, in which the measured pressures are used to determine when and where the dimples should be actuated. This would require a control model, that is a clear expectation of how we would wish the flow to be. Each model would be very dependent on a great many conditions, not least the type of flow.