If a moving vehicle (van) had a 10cm diameter aperture in the bodywork at the front, which forms the mouth of a sealed container within the vehicle, would the drag experienced by the vehicle increase in proportion to the size of the sealed container? In other words, would it matter if the sealed container had an internal volume of, say, 10 litres, or considerably larger? Likewise, would the shape of the container have any bearing on the drag: i.e. would a conical container with its base at the opposite end to the mouth perform differently than an inverted cone shape with the mouth in the widest part of the container? I will be grateful to anyone who can provide me with the relevant maths.